Re: key misses in memcached
Baskaran Sankaran wrote: The key miss problem occurs, when I store all the three keys and their values for the rules. I guess that the problem is due to the fact that the every key is similar to two other keys except for the suffix part, though I don't understand why this is a problem. I would greatly appreciate any help. You could simply be running out of memory - or there could be some kind of hash collision happening that would not be a problem the way memcache is normally used with an underlying database holding the authoritative copy. However, you may have an even bigger problem since you want to update the values from multiple processes and you won't have any locking. This seems like a problem that mysql or postgresql would solve easily in a machine with sufficient RAM. Memcache is normally used where you want to read the same value thousands of times without bothering the underlying backend database. -- Les Mikesell lesmikes...@gmail.com
Re: New "wait timeout" argument for the get() method.
Dustin wrote: On Mar 25, 9:31 am, gf wrote: Thank you for your anwer. I can pay if necessary. How much it costs? I can build you a custom version of memcached that does whatever you want, but you'd have to consider: 1) This will not be part of the core memcached server -- so you'll be kind of stuck with whatever build I make you. 2) If you wanted to also run this as a memcached instance, the data loss properties that make memcached such a good cache would conflict with your lock/queue goals. Also, I don't think it's a very good idea, so a lot of the negotiation time would be me trying to talk you out of it. :) If you put this in the server, don't you set up conditions for: A) all clients trigger the wait and thus deadlock and/or B) some number of clients run the server out of resources ?? -- Les Mikesell lesmikes...@gmail.com
Re: New "wait timeout" argument for the get() method.
gf wrote: А) It's possible if the timeout is big, I intend to use 0.1 as the timeout. Blocking everything for .1 sec would be a very bad thing. Is the update supposed to be done by one of the same clients that can be hung in this wait? How does the updater distinguish itself from the rest? B) It's possible. But the same (or lower) number of clients repeating get() every several ms run the server out of resources early. A failing get() should only use time on the server - a resource that goes by whether you use it or not. Waiting will consume an assortment of things to maintain the state - and should be done on the clients where the resources scale up with the number of them. -- Les Mikesell lesmikes...@gmail.com
Re: New "wait timeout" argument for the get() method.
gf wrote: How does the updater distinguish itself from the rest? acquire() (atomic add). So a whole bunch of clients try to add some sort of key that you hope are identical so all but one fail, the one that succeeds is supposed to do some more work? What if its next step fails? -- Les Mikesell lesmikes...@gmail.com
Re: memcached not always work
expream wrote: Hello all! I'm new to memcached. And hove some problems. I have a online game ... and I'm using memcached... but sometimes I see that memcached dont work.. 1 time from 20 memcached returned 0 instead of value... what can be the problem? I have pretty high load... netstat -np 11211 | wc -l is about 6 ... and there are a lot of TIME_WAIT connections... what parametrs shuold I change... if I have a lot of visitors... ? I've forgotten the exact values, but there is a theoretical limit to the number of TCP connections and the rate you can make them to a single IP address and port. There's a 16-bit socket value combined with IP/port to find the end point, so you can only have 64k with the same IP/port open at once, and sockets are not re-used for the time it might take for a lost packet to make a round trip so it won't be associated with the new connection (that's your TIME_WAIT). If you really need more than 64, connections to one port, you'll have to add another IP address and round-robin to load balance them. If you have fewer end points, each making new connections frequently, perhaps they can maintain a connection and re-use it. -- Les Mikesell lesmikes...@gmail.com
Re: Memcached monitoring/statistics tool
Josh Snyder wrote: We have sizeable number of memcache instances running. We have some simple Nagios alerts mainly checking for reachability and a handful of Cacti graphs. However, in practice, memcached is extremely stable, so we only get alerts when we've screwed something up, and the Cacti graphs see pretty light usage. I wouldn't go nuts on worrying about monitoring your memcache servers beyond the basics until you have a solid sense for what your needs are; I would focus instead on carefully monitoring your clients. Does anyone deploy spare machines with some way to pick up the IP addresses of any that fail, or do you just make them all active and let the client re-balancing take care of any problems? -- Les Mikesell lesmikes...@gmail.com
Re: project division
maciejplonski wrote: Hello, I've got memcached installed on my VPS and also I've got there blogging platform. I'm caching whole pages in memcached and serving them by nginx. When one user posts sth, I need to flush whole memcached and delete from cache also other cached blogs. Is it possible to divide memcached to many 'blogs' and flush only cache from one blog so other blogs will be still served from memcached? This blogging platform is written in PHP. If you know when and what you need to delete, why not just update the cache instead and not break anything else? Or, keep track of an update count somewhere that you use in a key prefix so when a new post happens you just stop using the old copies and they'll age out naturally. -- Les Mikesell lesmikes...@gmail.com
Re: project division
maciek wrote: I like the idea with unique keys, but the problem is I'm loading data from memcached by nginx, so keys must be in format '$http_host $request_uri'. Don't these get the article number as a component so new ones take care of themselves except perhaps for a posters home with the current list? Maybe you can make the home page have an iframe so the current list always checks the application - which can cache this at a component level. idea with re-caching data - I'm not caching all pages from all blogs, on only that one visited in last 10h If you put stuff in that nobody wants it will be discarded as the least recently used when another item needs space - no need to do extra work to do that explicitly. -- Les Mikesell lesmikes...@gmail.com
Re: project division
Clint Webb wrote: Rather than using memcached as a global site cache (which it is not really designed to be), you might have more success actually using it the way it was intended. Which means as an object cache inside your code. Otherwise you are just going to be doing a lot of effort to get a square peg to fit in a round hole. There's not really anything wrong with using it as a page cache as well. You just can't set the expire time on pages to a time past when they will change. -- Les Mikesell lesmikes...@gmail.com
Re: project division
Clint Webb wrote: On Sun, May 3, 2009 at 8:58 AM, Les Mikesell wrote: Clint Webb wrote: Rather than using memcached as a global site cache (which it is not really designed to be), you might have more success actually using it the way it was intended. Which means as an object cache inside your code. Otherwise you are just going to be doing a lot of effort to get a square peg to fit in a round hole. There's not really anything wrong with using it as a page cache as well. You just can't set the expire time on pages to a time past when they will change. On dynamic sites where you have to either delete your entire cache whenever any changes are made to a single page, or you must go through extraordinary measures to get around that limitation there certainly is. If you can break what looks like a dynamic page into iframes that hold versioned contents, you can still cache a large percentage of the content at the http level. You are right that there are cases where using it as a cache is appropriate. Actually I have used it to cache entire pages that are dynamically generated, but not changed once generated Other than that, I cant think of a good use for it where other solutions aren't better. It doesn't have to be an either/or proposition. If you have a page frame that is uncached or has a short expire time, the underlying app just has to compute the appropriate urls to the cachable but versioned parts and you only have to generate those once. -- Les Mikesell lesmikes...@gmail.com
Re: Cache "fails" when doing high volume of simultaneous read/write requests
Pallab Bhattacharya wrote: On Sun, May 3, 2009 at 7:31 AM, Syed Ali wrote: How much memory are you giving to it? And how big are your objects? It could be that they get evicted to make space for new onesand therefore you dont find them in cache it appears from his description that he uses the same key - so when it is paced - there is a cache-hit because the first request would have populated the cache with the key. when he tries to race - obviously all threads face the same truth - the looked up object is absent - so they all try to replenish the missing object hence goes to db simultaneously, So it is probably the concurrent activity at the db that slows it down and makes the problem visible. That seems like it might be a common problem for sites where new items appear that might be very popular as soon as the link becomes visible. Is priming the cache as these items are generated the best way to avoid this - or does it really just show up in automated testing? -- Les Mikesell lesmikes...@gmail.com
Re: memcached log file
rwthomas wrote:
Yes, I understand that a service runs a script. With memcached 1.2.2,
you could specify the logfile in the startup script (memcached-start)
in the /usr/local/bin dir. The new version of memcached does not use
memcached-start. I have tried to add redirects to the start script,
but the only thing it puts in the file that I am redirecting to is the
OK that comes when you start or stop the service. the memcached-start
file is actually a perl script. Below is an example of what we used
to run:
#my $fd_reopened = "/dev/null";
my $fd_reopened = "/root/mem.log";
sub handle_logfile {
# my ($logfile) = @_;
my ($logfile) = "/root/mem.log";
$fd_reopened = $logfile;
}
sub reopen_logfile {
# my ($logfile) = @_;
my ($logfile) = "/root/mem.log";
open *STDERR, ">>$logfile";
open *STDOUT, ">>$logfile";
# open *STDIN, ">>/dev/null";
open *STDIN, ">>$logfile";
$fd_reopened = $logfile;
as you can see, we redirected to mem.log. When we upgraded, we found
that memcached 1.2.8 does not use the memcached-start perl script.
that is why I am trying to find a way to do this again.
We are running CentOs 5.2 with memcached 1.2.8
Centos inherits the RedHat style init scripts which typically use the
daemon() function in /etc/rc.d/init.d/functions to start programs - and
it redirects stdout and stderr to /dev/null among other things. You'll
probably have to make the /etc/init.d/memcached script do the same
things directly instead of using daemon() so you can control the
redirection yourself. It would be a little handier for this style of
control if memcached had a command line option like '-o logfile' so it
could be controlled in the options the script sources from
/etc/sysconfig/memcached and expands on the command line.
--
Les Mikesell
lesmikes...@gmail.com
Re: Is memcached for me?
JonB wrote: By the sound of it, memcached will work - it'll cost me network calls (but not to the MySQL server) - the only remaining doubt I have is over the data being stored in it. If you are already doing network calls to mysql it is a pretty sure thing that memcached will not be slower than even a 'fast' mysql response on cache hits. Not a lot of our data can be agregated before being cached - so we're left again, looking in the cache for very small bits of data (a few bytes to a few hundred bytes). I'll have to sit down and work out where in the application it's likely to sit, and whether the cost of the network calls etc. to get a few bytes, is actually worth it. I guess having a 'localhost' cache would avoid some of the overhead, as would UDP. Memcache will be somewhat slower than caching in the app's memory, but you trade that off for having to duplicate the RAM and initial fetch for each server and having the items expire at different times on each server. -- Les Mikesell lesmikes...@gmail.com
Re: memcached slower than file IO
Ved wrote: Thanks David for your reply but what I mentioned are not my assumptions 1. memcached is installed on the machine where my file is so that takes care of your concern ( memory on a different machine ). That doesn't matter - you still go through the same client/server motions to access it through a socket as if you have distributed storage. 2. I am not just reading a single file everytime. I have 3 data files that I access in the script (system may be caching files in memory) 3. Even if the files are not changing does it mean that disk cache is faster than memcached? that too an extent of disk cache being almost 50% faster than memcached. Yes, if you have sufficient RAM, all recently accessed file data will be cached at the OS level for fast repeated access. I am sorry, but I don't think your explanation addresses my concerns. The part that didn't make sense was that you mentioned memcache having many failures. Unless you have not provided sufficient RAM, you should only fail on the first access to new or expired data. Perhaps with memcached running you don't have enough memory to hold your active data set in either the memcache cache or the now reduced filesystem buffers and end up making them both thresh. -- Les Mikesell lesmikes...@gmail.com
Re: memcached slower than file IO
Ved wrote: There is 8 GB RAM on the server, and on first access apache bench doesn't show any failed requests, but if I execute the program again, I see that number of failed request show up, this is something that I couldn't understand as why didn't the number of failed request show on the first run and then appears every subsequent run (Total request for each run : 10,000 and 200 cc). Are these apache errors or errors in memcache? If you are running a high concurrency in apache benchmark you may be running the server out of sockets or some other resource. "Perhaps with memcached running you don't have enough memory to ...". this is not the case in any which ways, have checked the memory and had that been an issue even file IO would have more or less given me the same performance. I think you are missing the point that if you had just enough room for the data in the file buffers without memcache, then allocate a portion to memcache, neither one would have enough space and both would have to continuously reload the data as it is evicted. -- Les Mikesell lesmikes...@gmail.com
Re: memcached as http cache
googleuser wrote: Hello, I have some problems with apache. If I use squid as proxy-cache I have auth problems. And if I use mod_cache do not work because mod_cache uses rewrited url and not requested url (all pages are the same for mod_cache). These problems are hitting me to implement new http caching engine. I think that memcached could be useful for this. Anyone have some experience or info about memcached as http cache engine. Performance, memory issues, posible implementations,...? I haven't tried it, but this approach sounds fast: http://www.igvita.com/2008/02/11/nginx-and-memcached-a-400-boost/ But what kind of auth problem do you have with squid? -- Les Mikesell lesmikes...@gmail.com
Re: Using memcached as a distributed file cache
dormando wrote: You could put something like varnish inbetween that final step and your client.. so key is pulled in, file is looked up, then file is fetched *through* varnish. Of course I don't know offhand how much work it would be to make your app deal with that fetch-through scenario. Since these files are large memcached probably isn't the best bet for this. You could also redirect the client to the proxy/cache after computing the filename, but that exposes the name in a way that might be reusable. -- Les Mikesell lesmikes...@gmail.com
Re: How to check status of the server which will be chosen by Hashing Policy
Henrik Schröder wrote: Unfortunately most client libraries perform server selection slightly differently from each other. It might be possible to get the same distribution if you use the naive server selection in both, and setup your list of servers the same way. On the other hand, does it really matter? Changing your cache client is kinda a big deal, I wouldn't do that on a running system, what if you have processes that are in the middle of changing your cached data? No, your best option is to bring your application down, release the change, and bring it back up again. You might also want to flush the cache to make sure you won't get any synchronization errors. On the other hand, it shouldn't matter. The worst thing that should happen if one client picks a different server than another is that you use the memory less efficiently and you'll hit the backend data store a bit more frequently. If you are counting on everything having a time-synchronized view of exactly the same data, you probably shouldn't be using a distributed cache. -- Les Mikesell lesmikes...@gmail.com
Re: Any plan for libev support?
The link is actually to a BSD-ish 'retain the copyright notice' license, with the GPL permitted as an alternative. Trond Norbye wrote: Then I guess the answer is no, because memcached is BSD... Trond Sent from my iPhone On 20. feb. 2010, at 16.23, Ryan Chan wrote: On 2月18日, 下午11時27分, Paul Lindner wrote: I didn't see any mention of the license. libevent is bsd, which integrates well with the memcached license. http://cvs.schmorp.de/libev/LICENSE?view=markup GPLv2
Re: Memcache as session server with high cache miss?
On 3/10/2010 10:28 AM, Brian Hawkins wrote: Explain how using memcached opens one self to a DOS attack? If you are expecting it to be a persistent store by itself, simply exceeding capacity will drop data before you expect it to expire. Of course if your sessions are tied to logins this would be harder to cause, and if you have a backing DB of critical entries then it's not a problem until you overwhelm the DB. Memcache itself isn't a problem unless you expect it to always have your data, which it isn't intended to do. -- Les Mikesell lesmikes...@gmail.com
Re: Memcache as session server with high cache miss?
On 3/10/2010 10:52 AM, Carlos Alvarez wrote: On Wed, Mar 10, 2010 at 1:28 PM, Brian Hawkins wrote: Explain how using memcached opens one self to a DOS attack? Using memcached to store session data just relying in a previous calculation of how many memory you will need (all premises) exposes you to DOS because of the effect explained in other mails: it would be very easy and some attacker would need a very low bandwith to force the memcached to expell valid data. If your application relies on data to be present on the memcached to work properly, you have a problem. If you have a persistent store, it won't expell data because of space constraints. Also, I find a lot more easier (and cheaper) to have a 4TB persistent store than a set of memcached. But you'll find it very expensive to scale up the number of servers accessing that persistent store and the speed it can operate if you don't use something like memcache in front of it. -- Les Mikesell lesmikes...@gmail.com
Re: Memcache as session server with high cache miss?
On 3/10/2010 5:14 PM, moses wejuli wrote: Yes, good point as far as service interruption is concerned but I don't see how this affects performance, especially if the programmer carefully uses this feature for tiny amounts of data per user I just think, given how far memcache has metamorphosed, the time is probably right to include such a feature (to be used with some care of course) You can't count on nothing ever going wrong. How should this theoretically reliable storage mechanism respond to a network glitch to one or more of the servers? Or just a miscalculation in terms of how much data you throw at it? -- Les Mikesell lesmikes...@gmail.com
Re: Memcache as session server with high cache miss?
On 3/10/2010 5:46 PM, moses wejuli wrote: it's not so much a /"theoretically reliable storage mechanism"/ but only storing data for as long as the programmer chooses or in this case, for only as long as the user is logged on (data is expelled when the user chooses to log out or is forcibly logged out for one reason or another). Or until any component fails, needs a change, etc. data miscalculation? i think you'd have to take care as a /dev/ for this not to happen -- infact this is presently the case (think max slab size) I'd guess that it's uncommon for memcache users to have any idea how many potential keys might be in use at once (constructing them from arbitrary sql queries, etc.). Or to do anything to remove data. You really can't iterate over it to see what needs to be removed - and where else would you store the keys so you'd know about them? -- Les Mikesell lesmikes...@gmail.com
Re: Memcache as session server with high cache miss?
On 3/11/2010 1:01 PM, Martin Grotzke wrote: Hi, I'm trying to follow this thread on my mobile, i hope i didn't miss anything. But AFAICS it was not yet explained, when memcached might drop cached data as long as there's enough memory and expiration is not reached. Or is this not deterministic at all? Perhaps you can point me to resources providing more details on this? 'Enough' memory may not be what you expect unless you understand how your data fits in the allocated slabs. And I'm not sure what happens if the keys have hash collisions. -- Les Mikesell lesmikes...@gmail.com
Re: Memcache as session server with high cache miss?
On 3/12/2010 11:21 AM, martin.grotzke wrote: Hi, I'm trying to follow this thread on my mobile, i hope i didn't miss anything. But AFAICS it was not yet explained, when memcached might drop cached data as long as there's enough memory and expiration is not reached. Or is this not deterministic at all? Perhaps you can point me to resources providing more details on this? 'Enough' memory may not be what you expect unless you understand how your data fits in the allocated slabs. And I'm not sure what happens if the keys have hash collisions. What about setting the minimum slab size to 1 mb (-n 1048576) so that there's only one slab and one can calculate with this? After seeing more of this thread, I'm inclined to think that the problem that started it is really a misconfiguration or network issue. While you shouldn't expect memcache to be a reliable store, the miss percentage should not double when you add another server. -- Les Mikesell lesmikes...@gmail.com
Re: How to get more predictable caching behavior - how to store sessions in memcached
On 3/12/2010 5:10 PM, Martin Grotzke wrote: With my question "how do I have to run memcached to 'store' these sessions in memcached" I was not referring to a general approach, but I was referring to the concrete memcached options (e.g. -n 204800 for 200kb slabs) to use. The post you mentioned is very high level and does not answer my question. For this you should go into a little more depth. Some details here: http://dev.mysql.com/doc/refman/5.0/en/ha-memcached-using-memory.html But it's still not very clear how much extra you need to make sure that the hash to a server/slab will always find free space instead of evicting something even though space is available elsewhere. -- Les Mikesell lesmikes...@gmail.com
Re: How to get more predictable caching behavior - how to store sessions in memcached
dormando wrote: To be most accurate, it is "how many chunks will fit into the max item size, which by default is 1mb". The page size being == to the max item size is just due to how the slabbing algorithm works. It creates slab classes between a minimum and a maximum. So the maximum ends up being the item size limit. I can see this changing in the future, where we have a "max item size" of whatever, and a "page size" of 1mb, then larger items are made up of concatenated smaller pages or individual malloc's. So what happens when a key is repeatedly written and it grows a bit each time? I had trouble with that long ago with a berkeleydb version that I think was eventually fixed. As things work now, if the new storage has to move to a larger block, is the old space immediately freed? -- Les Mikesell lesmikes...@gmail.com
Re: How to get more predictable caching behavior - how to store sessions in memcached
Martin Grotzke wrote: Tomcat sounds like such a pisser :P Even with your backup thing I'd probably still add an option to allow it to journal to a database, and I say this knowing how to get every last ounce of efficiency out of memcached. Tomcat provides a PersistentManager ([1]) which allows to store sessions in the database. But this manager backups all sessions in batches every 10 seconds. For one thing scalability of the application is then directly dependent from the database (more than it is already if a database is used) and there's a timeframe where sessions can be lost. If the session backup frequency is shortened, the database is hit more often. Additionally sessions are stored in the database again and again even if they were not changed at all. That was the reason why I decided not to use this. What about tomcat's ClusterManager? Doesn't that provide replication across server instances? -- Les Mikesell lesmikes...@gmail.com
Re: How to get more predictable caching behavior - how to store sessions in memcached
Adam Lee wrote: well, it depends on what you mean by scalability... i'm personally of the opinion that traditional sessions should be avoided if you want to truly scale. And yet, everyone wants dynamic pages custom-generated to the user's preferences. So how do you reconcile that? You can help things a bit by splitting pages into iframe/image components that do/don't need sessions, and you can make the client do more of the work by sending back values in cookies instead of just the session key, but I'm not sure how far you can go. -- Les Mikesell lesmikes...@gmail.com
Re: Memcached as web page cache
On 5/19/2010 1:46 PM, Sun-N-Fun wrote: Apache Traffic Server looks good! Has commands for deleting a specific object from the cache. I hadn't been paying attention. Is that released and ready for prime time now? -- Les Mikesell lesmikes...@gmail.com
Re: Is this really Distributed?
Dilip wrote: We read that memcached is "Free & open source, high-performance, distributed memory object caching system" Where as "distirbuted" is not part of memcached servers. We have to have some client which knows about all memcached servers and uses some hash based on key to determine a server. Is My understanding correct? If it is correct, we should remove "Distributed" from the above definition. The data is distributed - but the servers don't need to know anything about that. Doesn't that still make it a distributed system? -- Les Mikesell lesmikes...@gmail.com
Re: Is this really Distributed?
Dilip wrote: Going by that definition: All client server architectures are distributed. like ftp, ldap, sql servers are all distributed. How is the data distributed across many servers in these services? As i understood, in distributed systems there is no single point of failure. Memcache is sort of a special case in that not finding a cached item is not a failure - it is an expected event and the client is expected to retrieve the data from the actual source and refresh the cache. If a server fails, this cache refresh will go to a different server. but in all these cases there are single point of failures. internet is distributed because there is no single point of failure. But after looking at the link http://en.wikipedia.org/wiki/Distributed_computing, here client server architecture is termed as distributed. I think the responsibility of not having single point of failure is to have intermediary clients, which can do that. Now I think we can call it that way. A cache server failure shouldn't have any visible effect other than making the source servers work harder while the data it held is refreshed onto the remapped servers. -- Les Mikesell lesmikes...@gmail.com
Re: Problems with ping latencies...
On 6/18/2010 2:41 PM, Ryan Amos wrote: The only thing installed on this server is memcached, so all the connections are memcached connections. It's also the only port open via iptables, other than one additional port for monitoring software. It's not necessarily that machine. I'm more curious if anyone has had this problem before and knows how to solve it. This is probably the wrong place to diagnose network problems, but you need to look at network capacity and traffic across the equipment between the machines. You might have something else using all the bandwidth or perhaps a duplex mismatch at a switch port. -- Les Mikesell lesmikes...@gmail.com
Re: Scalability and benchmarks
On 6/30/2010 5:35 PM, dormando wrote: With what kind of boxes would that be? With 300-500k/sec you're getting really close to lowlevel limitations of single network interfaces. With dell 1950's (with broadcom netextreme II 5708 and dual xeon 5150) we were able to produce about 550-600,000 packets/second with traffic/load-generating software (pktgen in the linux kernel) to test ddos protection. And that was with fire-and-forget 64byte tcp or udp-packets. Not with traffic some server was actually producing useful responses to requests it received earlier. With a much more recent Dell R210 (broadcom netextreme II 5709 and core i3 530) we were able to reach twice that though. That one was able to reach about 1.1 million pps. But still, that's with a packet generator generating unusable traffic. If you actually have to read the requests, process them and produce a response with a body, reaching up to 500k requests/second even on higher grade hardware with multiple interfaces sounds pretty good to me. For most hardware memcached is limited by the NIC. I'd welcome someone to prove a simple case showing otherwise, at which time we'd prioritize an easy fix :) Does that mean you should use multiple NICs on the servers and spread the clients over different networks? -- Les Mikesell lesmikes...@gmail.com
Re: Scalability and benchmarks
On 7/1/2010 9:37 AM, dormando wrote: Given the title, the overtly academic content, and the lack of serious discussion as to the application of such knowledge, we end up with stupid threads like this. Imagine how many people are just walking away with that poor idea of "holy shit I should use REDIS^WCassandra^Wetc because memcached doesn't scale!" - without anyone to inform them that redis isn't even multithreaded and cassandra apparently sucks at scaling down. Google is absolutely loaded with people benchmarking various shit vs memcached and declaring that "memcached is slower", despite the issue being in the *client software* or even the benchmark itself. People can't understand the difference! Please don't confuse them more! There are *many* more interesting topics with scalability gotchas, like the memory reallocation problem that we're working on. I have the cache spread across about 20 servers per site, with the servers also doing some other work, and could add more if the performance of a single server ever becomes an issue. The question I find more interesting and probably a lot harder to nail down is what kind of performance impact will it have if one or a few of the servers go down at a busy time. Ignoring the impact on the origin servers, how long does it typically take a client to figure out that a server is gone and what happens if it is supposed to be fielding 100k requests/second at the time? And do all the different clients rebalance in the same way once they notice a configured server is dead? In real-world situations I think the client performance is much more important than the server, especially since in this case it has to deal with the load balancing and failover logic - and you can just add more servers if you need them. -- Les Mikesell lesmikes...@gmail.com
Re: stats help
Dustin wrote: On Jul 24, 10:39 pm, Spike wrote: hi, i am newbie to memcached. I need help in finding how to get throughput stat. I want to see how much throughput memcache is getting. "stats" command does not list any stat for through put (requests per sec). Any idea on how to go about getting that info? Does memcache keep track of this information? It's rare to keep derived stats like that in general. It's usually not interesting. Do you want average requests per second over the lifetime of the process? Over the last second?, 60 seconds? 300, 900, 3600, etc... Most of the time, this is easily observable from the outside. Collect counters -- wait a bit, collect them again, then do your own math. That'll give you exactly what you want. It's a bit off topic for this list, but does anyone know if there are good generic tools for that? There are quite a few designed to convert SNMP 'COUNTER' types to rates, check thresholds and keep history to graph the trends, but usually the SNMP sampling is closely coupled to the rest of the logic. I think OpenNMS might do it with values it can pick up with http requests but I'm not sure how well it handles the spikes that would appear from restarts and value rollovers. -- Les Mikesell lesmikes...@gmail.com
Re: stats help
I know rrdtool (and the jrobin equivalent in java) can do it, but that's a fairly low level tool. I was hoping to find some generic framework that could accept either counter or gauge type values and do the rest for you including a web graph display. I'd think this would be a common problem but I haven't found any high-level tools that aren't married to snmp for the input. -Les Gavin M. Roy wrote: I use RRDTool for this with derive counter types. Collect the data you want from the stats command and use rrdtool to store the data every minute, graph it out with rrdtool graph and you'll get your trended stats. hi, i am newbie to memcached. I need help in finding how to get throughput stat. I want to see how much throughput memcache is getting. "stats" command does not list any stat for through put (requests per sec). Any idea on how to go about getting that info? Does memcache keep track of this information? It's rare to keep derived stats like that in general. It's usually not interesting. Do you want average requests per second over the lifetime of the process? Over the last second?, 60 seconds? 300, 900, 3600, etc... Most of the time, this is easily observable from the outside. Collect counters -- wait a bit, collect them again, then do your own math. That'll give you exactly what you want. It's a bit off topic for this list, but does anyone know if there are good generic tools for that? There are quite a few designed to convert SNMP 'COUNTER' types to rates, check thresholds and keep history to graph the trends, but usually the SNMP sampling is closely coupled to the rest of the logic. I think OpenNMS might do it with values it can pick up with http requests but I'm not sure how well it handles the spikes that would appear from restarts and value rollovers. -- Les Mikesell lesmikes...@gmail.com <mailto:lesmikes...@gmail.com>
Re: REST API
On 7/28/2010 10:16 AM, jsm wrote: Gavin, You are right about the overhead and also saw that API's exist for most of the languages as well. I thought REST API would make memcached language agnostic. I would like to hear from the community if the REST API should be pursued or not? I'm not quite sure how a rest api could deal with the distributed servers without a special client anyway. But, it might be handy to have a web service that mapped a rest api as directly as possible to memcache operations where the http side would use traditional load balance/fail over methods and handle the http 1.1 connection caching. I'm sure there would be places where this could be used by components that have/want data in a cache shared by more efficient clients. -- Les Mikesell lesmikes...@gmail.com
Re: REST API
There's no argument that embedding a locally-configured memcache client
library for the appropriate language into your program would be more
efficient, but consider the case where you have many programs in many
languages sharing the cache data and some of them have inherent http
capability and aren't used enough to care about that last 10% efficiency
when it means rewriting a bunch of code with new libraries to get it.
However, I still think the http interface would have to be a separate
standalone piece, sitting over a stock client that knows about the local
distributed servers or you'd need a special client library anyway.
-Les
On 7/28/2010 12:53 PM, Adam Lee wrote:
memcached's protocol is, as has been pointed out, already language
agnostic and much more efficient than trying to do HTTP. If you're
saying RESTful in the "not necessarily HTTP" sense, though, then I'd say
that memcached's text protocol is basically already as RESTful as you're
going to get- think of commands as verbs ('get,' 'set,' 'add,' 'delete,'
etc...) and the key as a URI and you're basically in an analogous
situation that I think basically meets the criteria as much as you can
(hard to have a stateless cache)...
http://en.wikipedia.org/wiki/Representational_State_Transfer#Constraints
If you want a key-value datastore with an HTTP interface, though, might
I recommend Tokyo Tyrant? It speaks memcached and its own binary
protocol as well: http://1978th.net/tokyotyrant/spex.html#protocol
On Wed, Jul 28, 2010 at 12:03 PM, Les Mikesell mailto:lesmikes...@gmail.com>> wrote:
On 7/28/2010 10:16 AM, jsm wrote:
Gavin,
You are right about the overhead and also saw that API's exist for
most of the languages as well.
I thought REST API would make memcached language agnostic.
I would like to hear from the community if the REST API should be
pursued or not?
I'm not quite sure how a rest api could deal with the distributed
servers without a special client anyway. But, it might be handy to
have a web service that mapped a rest api as directly as possible to
memcache operations where the http side would use traditional load
balance/fail over methods and handle the http 1.1 connection
caching. I'm sure there would be places where this could be used by
components that have/want data in a cache shared by more efficient
clients.
--
Les Mikesell
lesmikes...@gmail.com <mailto:lesmikes...@gmail.com>
--
awl
Re: REST API
On 7/28/2010 1:43 PM, Marc Bollinger wrote: "and some of them have inherent http capability and aren't used enough to care about that last 10% efficiency when it means rewriting a bunch of code with new libraries to get it." But you're..._adding_ support for memcached to that system. If this were a system already using memcached, it'd be...speaking memcached. If it were using a different, external caching system, you'd probably expect some measure of integration code, or at least testing it if, like Tyrant, it did speak the same protocol you were expecting. The only other case would be if you weren't using some external cache already, in which event you're going to be adding logic, regardless. I think we don't have the same concept of "the system". Mine is that unrelated programs may be using the same data and only some of them are designed around memcache and need its speed. Maybe it would be better to embed memcache into a traditional http proxy for the things that don't to avoid having the cache miss logic everywhere. -- Les Mikesell lesmikes...@gmail.com
Re: REST API
On 7/29/2010 8:54 AM, j.s. mammen wrote: Folks, lets not get bogged down by REST defined by Roy Fielding in 2000. My question was simple. Here it is again, rephrased. Do we need to implement a memcached layer whereby we can access the cached objects by using HTTP protocol. Here is an example of getting a cached object from a server GET [server]/mc/object/id1 Hope the question is clearer now? I can see an advantage if it let you get/put data using facilities most languages have built-in instead of needing an add-on client library. But, I don't see how you would handle the [server] part without re-creating all of the logic in the client library anyway. -- Les Mikesell lesmikes...@gmail.com
Re: Don't quite understand why expiration is necessary
On 8/3/2010 12:41 PM, Peter wrote: Thank! Now it makes more sense to me! Dustin, how do you do to avoid expiration date in your application? For most of the places where you would use memcache it shouldn't matter. That is, your persistent backend data store should be hand cache misses (for any reason, including expirations) and the point of the cache is just to not overwhelm it with thousands of requests for the same thing. -- Les Mikesell lesmikes...@gmail.com
Re: 1TB memcached
On 9/21/10 1:26 AM, MikeG. wrote: Sorry I used blob to describe the final deliverable bundle not DB blob. As far as having partial objects in memory - this should never happened based on my intended design. I would like to have the entire DB permanently in cache. Since I don't have that much RAM on one machine I plan to use virtual memory or memory mapped files. In this case my only limit is as big as my hard drive I'll get. Why do you expect the file activity of virtual memory to be any faster than a traditional database designed to use files efficiently? I'd expect the opposite. You should generally assume that the disk head is going to be halfway across the disk from the data you want and add up the seek time it will take to get there. On the other hand, using real memory across several machines is very fast. -- Les Mikesell lesmikes...@gmail.com
Re: 1TB memcached
On 9/22/2010 11:59 AM, Matt Ingenthron wrote: On 9/22/10 6:12 AM, ligerdave wrote: MongoDB is actually "cached" db, meaning that, most of its records are in memory. I think there is also a memcached and DB hybrid which comes w/ a persistent option. i think it's called memcachedDB, which runs a in- memory db(like mongodb). this shares most of common api w/ memcached so you dont have to change code very much membase is compatible with memcached protocol, has a 20MByte default object size limit, lets you define memory and disk usage across nodes in different "buckets". memcacheDB is challenging to deploy for a few reasons, one of which is that the topology is fixed at deployment time. Does anyone know how these would compare to 'riak', a distributed database that can do redundancy with some fault tolerance and knows how to rebalance the storage across nodes when they are added or removed? (Other than the different client interface...). -- Les Mikesell lesmikes...@gmail.com
Re: Is memcache add() atomic on a multithreaded memcached?
On 10/17/10 6:07 AM, Tobias wrote:
Is it ever possible that your compute takes longer than your timeout?
no, the return value of "memcache.delete("lock" + x) is true.
But wouldn't that also be true if another process found the expired lock and set
a new one?
--
Les Mikesell
lesmikes...@gmail.com
Re: features - interesting!!
On 2/3/11 11:40 PM, Roberto Spadim wrote: LOCK (create a key-value, always return value) UNLOCK (delete key-value, if key-value=sent(key-value) delete, return before delete value, if not exist return blank or null) that's it easy not? What happens when the server holding the lock value is rebooted? Or needs to evict values from memory? For memcache's real purpose those things don't affect operation because the client will reload the correct values on the next access. Where is the persistent backing store for this value? > timeout could work too (it's key-value based) Memcache is a cache, not a key-value store. -- Les Mikesell lesmikes...@gmail.com
Re: features - interesting!!
On 2/4/2011 9:34 AM, Roberto Spadim wrote: What happens when the server holding the lock value is rebooted? Or needs to evict values from memory? For memcache's real>purpose those things don't affect operation because the client will reload the correct values on the next access. Where is the>persistent backing store for this value? if elockd/lockd/any other lock server die, what happen? (non vollatile or vollatile? it's a app problem not memcache problem, app must know what happen, just it. If they are designed to be reliable, the value will be stored redundantly and the system will know how to retrieve the copy that is still valid or an error if that is impossible. It is an application problem. It is not an error if a cache cannot return data. For a lock you must have the correct value or an error condition. And it doesn't make sense to have the memcache server check for the difference on every request when the client could just call an application designed for the more complex operation you need when it knows it needs a lock. with memcache we have volllatile, with memcachedb we have non vollatile, put at main memcache and i will work with memcachedb and repcache to sync this new feature at others memcache forks It probably can be done with membase. I don't think memcachedb is intended to be reliable. who will use memcache for lock and don't want loose keys change memcache command line to don't delete cache keys if cache is full non volatille? That still doesn't work in the usual scenario where you have many memcache servers and expect them to keep working even if some are down. timeout could work too (it's key-value based) Memcache is a cache, not a key-value store. nice, it's a cache (can loose information) it's a key-value store with timeout and volatille data, right? define cache! (volatile memory? how to cache? based on key-value? based on memory address? it's a key-value store! working as a cache! it could be a address-value store too, but it's a key-value store... and can loose information, app must know this!) A cache must have a method where the correct value can be retrieved when it is empty. How can either the clients or server replenish the value of the lock when it is gone for any reason? i use memcache for store some values with pic18f4550 and it's very good, since my pic have low memory and my server have a lot of memory Yes, it is very good for holding values for quick access that you are able to retrieve in some slower way. -- Les Mikesell lesmikes...@gmail.com
Re: features - interesting!!
On 2/4/2011 11:25 AM, Dustin wrote: easy? with it i can have 3 or more send/receive removed from my pic18f4550 code (save a lot of rom for me) Are you sure you're not looking for a job server (gearmand, beanstalkd, etc...)? Perhaps your mistake is in doing any of the processing on your PIC. Or if you are using it like a database, membase might be a better fit without making much difference on the client side. If you have another way of loading the data you could remove the part that handles cache misses from the client. -- Les Mikesell lesmikes...@gmail.com
Re: features - interesting!!
On 2/4/2011 11:40 AM, Roberto Spadim wrote: nice =] but it don´t have lock too :/ Isn't this a lock? http://wiki.membase.org/display/membase/getl+extended+operations I guess it is new and experimental. Then again, yours would be too. > today i´m using repcache, i never have problem with lose of information (i´m using a good ups too) the only problem is the PIC code is consuming a lot of ROM and time (many network i/o) and i can´t use many PICs in the same time since the network band is just 10mbit, in future i will replace to ARM with linux but today i can´t do that for many users :/ If you really need atomic operations, maybe redis would be better. -- Les Mikesell lesmikes...@gmail.com
Re: features - interesting!!
On 2/4/2011 12:40 PM, Roberto Spadim wrote: ehehe i know that there´s many others lock server, but i don´t have ROM on my PIC18f4550 to put two libraries =( it would be nice if i had a ARM or a x86 :/, but i don´t have :( if i use memcache i could do it with my PIC Do you already have enough of a library to make http client requests? A lot of the servers provide a rest interface. -- Les Mikesell lesmikes...@gmail.com
Re: features - interesting!!
On 2/4/2011 1:16 PM, Roberto Spadim wrote: i will learn more about redis, i didn´t see a lock server with cache yet my today app work today, but it´s not very good/fast (i have a network bootneck today) i rewrite to redis protocol is very poor :( if i can´t do anythink i will try a proxy between memcache and client and implement lock and unlock there, but it´s not so good, but solve my problem maybe in future put in memcache could be nicer =) i will study more and tell what i used thanks =] If you are relying heavily on your server anyway, why not put all of the application logic there and just speak http from the client? -- Les Mikesell lesmikes...@gmail.com
Re: features - interesting!!
On 2/4/11 9:56 PM, Roberto Spadim wrote: problem: today i need 4 packets to make 'lock'/'unlock' using memcache i need to use less ROM/CPU/RAM/network at client side What's the big picture here? If you want your client to do less work, why not run a web service on the server that not only implements the lock but also does most or all of what the client would have done while holding the lock? -- Les Mikesell lesmikes...@gmail.com
Re: Problems when one of the memcached server down
On 3/8/2011 1:40 PM, Evil Boy 4 Life wrote: Thanks guys, I turned off the failover in the client... In fact, I didn't know that there are several .net clients and now I get confused, because I don't know which one is better (now I use memcacheddotnet) Do you know if one of the .net clients support replication in any way? Memcache isn't supposed to do replication - it's a cache that you should be able to replenish from the real data source. What happens when one server fails depends on the client hash mechanism. Some people want the load to be rebalanced evenly over the remaining servers, some don't. Either way, the next attempt to use a failed server should detect it is down and retrieve the data from the backing DB. -- Les Mikesell lesmikes...@gmail.com
Re: It's a long story... (TL;DR?)
On 3/9/11 8:36 PM, dormando wrote: So when you CRUD against the database, you send another command with the UDF in it to DELETE or SET against the memcached cluster local to that database. You can pair it inside a dummy INSERT or UPDATE or trigger or sproc or whatever floats your boat. (unless I missed something and you don't use mysql at all). I thought the scenario was that he was updating a single master database which then replicates to remote read-only copies, and the client that just did an update may immediately read back a stale cache version from a different location instead of what it just changed. The real problem is the speed the replication propagates, so having the db push the cache update at each location probably can't fix it. -- Les Mikesell lesmikes...@gmail.com
Re: Implementation of CHECK command for memcached
On 3/18/2011 3:12 PM, Oleg Romanenko wrote: Hi. How could this be put to use? i.e. when is knowing that something exists at some point in an ephemeral store useful to an application? This command provides support for lazy read operation. You can read the value of the key only when is really necessary. For example: 1. I am storing some information about the client in memcached. The key - is the name of the session, which is is given to the client. 2. I have a lot of service scripts that should check the rights of clients. They need only to know whether there is a key (then everything is OK) or not (then the client is redirected to the login script). 3. And I have only two scripts that use the value of a key in they work. Of course, this problem can be solved by creating an additional (flag) key(s) without content. But such approach is less secure and in generally reduces the consistency of system's data (for example, key with data can be deleted when the flag key still remain available). Seems odd to not care about the content in a cache where you aren't guaranteed any relationship from one access to the next. That is, don't you have situations here where a check would say a key exists but when you try to retrieve it, it doesn't (expired, evicted, deleted by a concurrent operation, etc.)? -- Les Mikesell lesmikes...@gmail.com
Re: Implementation of CHECK command for memcached
On 3/18/2011 4:03 PM, Roberto Spadim wrote: check have a low network traffic, i think it´s a nice command Yes, and I don't see why it would be a problem to implement. I just don't see the point when by the time you get the answer it might not be true, and if you try to apply an new expire with it the underlying value for the key might have already been changed or removed. It just doesn't seem to mesh with the operations that work in a cache. -- Les Mikesell lesmikes...@gmail.com
Re: Implementation of CHECK command for memcached
On 3/18/2011 5:28 PM, Roberto Spadim wrote: hummm i think it´s a cache feature... for example, if a key of cache is key_1 , key_1_1, hey_1_2 , key_1_3, key_1_ if we check key_1 and it return not exists, we don´t need to check key_1_1,2,3,4 it´s a feature, some cache problems could get improvement with it. i think it´s very good =) think about http sessions just check if a variable exists in cache (it can be very big) if not exists get from session database (invalidade all cache values (delete)) What if the reason it doesn't exist is that it just got evicted - but some or all of your related keys might still be there? Or maybe the server holding that key just went down. if exists get all cache values from cache Likewise they may be evicted/expired separately. -- Les Mikesell lesmikes...@gmail.com
Re: Memcachd with httpd to cache user stickyness to a datacenter
On 4/11/2011 12:07 PM, Mohit Anchlia wrote: Yes it is a big deal for the business otherwise I wouldn't be posting it here asking for suggestions. I respect everyones input and thanksful for that, but I need to see if it will work for us too :) Agreed, it's not a rocket science. It is at least non-trivial to keep failover across data centers (which is often why you have more than one) but make sessions stick to one site as long as it is up, so it is worth putting some thought into it. Usually browsers will cache the IP address for the duration of a session anyway, but if you are running through a proxy it will repeat the DNS lookup frequently and switch addresses if you have alternatives. -- Les Mikesell lesmikes...@gmail.com
Re: Memcachd with httpd to cache user stickyness to a datacenter
On 4/11/2011 1:04 PM, Mohit Anchlia wrote: Yes that's correct. After giving it a thought and seeing how complicated this approach was becoming, we have decided to change our API calls to include user identifier in query string. We use LTM F5 and we will persist user info at F5 LTM with expiry set to 1 hr. If you have an LTM, you can just set its internal cookie persistence mechanism to tie a session to a particular server in the pool without doing anything different in the application. The initial connection will be balanced however the pool is configured. But that's only within the pool at a single data center (the L in LTM meaning local...) where the servers probably all have access to the same memcache service. -- Les Mikesell lesmikes...@gmail.com
Re: Understanding MemCached
On 7/21/2011 3:58 PM, Organic Spider wrote: Hi Brian, Yes have had a good read and still feel a little lost and stupid. What triggers each node to have the cache populated ? The client has to populate the data after a get attempt for a key fails. How does the data move between each node ? The other client's gets will succeed until the time to live expires. When that happens, the client making the failing request should pull a copy of the data from your database and refresh it in memcache. Or, is what I am requiring the repcached mod to replicate the data ? As long as your clients are configured with the same list of servers in the same order they will find a single copy. -- Les Mikesell lesmikes...@gmail.com
Re: Memcached as a distributed hash
On Thu, Aug 25, 2011 at 4:13 PM, Organic Spider wrote: > again am exploring how I may use memcached to distribute data between > multiple nodes; with one being the central hub. Yes I could use MySQL with > Master/N+slaves but that is such a large overhead on each node when it is not > really necessary. Have any of you used it for this purpose ? ie. central hub > either queries/or an insert/delete triggers and the data is pushed to a local > memcached instance which is then distributed between all other nodes. Each > node either 1) can detect that the memcache has updated 2) periodically uses > the memcache data to perform a task. > > Would be very interested on your input. That's not what memcache does. The value is only sent to and stored on one node, determined by hashing the key. -- Les Mikesell lesmikes...@gmail.com
Re: Several clients
On Fri, Aug 26, 2011 at 2:36 PM, Neeraj Agarwal wrote: > Thanks for sharing it. > > I'm an undergrad student so still lack on quite a things. > > Again, thanks! > > But, its so awesome to play with memcached. Just thought of this > point, so shared here :) > Note that having a temporarily different server list won't actually break anything any more than having one or a few servers down in a cluster with appropriate capacity, so you don't have to stop everything at once to reconfigure for more servers. You just end up with some higher percentage of cache misses and maybe some extra copies of data on other servers until it expires. -- Les Mikesell lesmikes...@gmail.com
Re: Memcached as a distributed hash
2011/9/9 Ted Zlatanov : > > No one here has tried Membase or Couchbase? That's surprising. I am > interested in them as compared to plain memcached so I hope this is the > right place to discuss them. > They are very different things. Memcache is used where you have some other persistent storage or way to generate the data and you want to avoid the overhead of making a query for repeated requests. If you are going to use something that also provides the persistent storage you need to consider whether you need more than key/value operations. -- Les Mikesell lesmikes...@gmail.com
Re: LONG-CONNECTION-SOCKET FOR PROTOCOL BUG
On Mon, Oct 31, 2011 at 9:51 PM, unique wrote: > Besides, it's a pity that Memcached can't support shared memory(on > Linux platform). the whole data-cache will All-lost just by updating > Memeached I think you are kind of missing the point of memcache if you you don't spread server instances over many machines so that restarting one (or a failure) just invalidates a small portion of the cache that your persistent data store can easily handle. If you want persistence, there are probably better tools. -- Les Mikesell lesmikes...@gmail.com
Re: recommended maximum number of nodes in memcache cluster (server pool)
On Sat, Nov 26, 2011 at 7:15 AM, Arjen van der Meijden wrote: > Wouldn't more servers become increasingly (seen from the application) slower > as you force your clients to connect to more servers? > > Assuming all machines have enough processing power and network bandwidth, > I'd expect performance of the last of these variants to be best: > 16x 1GB machines > 8x 2GB machines > 4x 4GB machines > 2x 8GB machines > 1x 16GB machines > > In the first one you may end up with 16 different tcp/ip-connections per > client. Obviously, connection pooling and proxies can alleviate some of that > overhead. Still, a multi-get might actually hit all 16 servers. That doesn't make sense. Why would you expect 16 servers acting in parallel to be slower than a single server? And in many/most cases the application will also be spread over multiple servers so the load is distributed independently there as well. -- Les Mikesell lesmikes...@gmail.com
Re: recommended maximum number of nodes in memcache cluster (server pool)
On Sat, Nov 26, 2011 at 2:05 PM, moses wejuli wrote: > @Les, you make a clear and concise point. thnx. > > In this thread, i'm really keen on exploring a theoretical possibility (that > could become very practical for very large installations): > > -- at what node count (for a given pool) may/could we start to > experience problems related to performance (server, network or even client) > assuming a near perfect hardware/network set-up? I think you can hit a point in number of requests in a multiget where increasing servers doesn't help speed up that single query (because you are limited by client cpu making the request), but having more servers isn't actually a problem. > -- if a memcacached client were to pool say, 2,000 or 20,000 connections > (again, theoretical but not entirely impractical given the rate of internet > growth), wud that not inject enough overhead -- connection or otherwise -- > on the client side to, say, warrant a direct fetch from the database? You will likely have to worry about the persistent backend database scaling long before that point. -- Les Mikesell lesmikes...@gmail.com
Re: recommended maximum number of nodes in memcache cluster (server pool)
On Sat, Nov 26, 2011 at 3:19 PM, Arjen van der Meijden wrote: > On 26-11-2011 19:28 Les Mikesell wrote: >>> In the first one you may end up with 16 different tcp/ip-connections per >>> client. Obviously, connection pooling and proxies can alleviate some of >>> that >>> overhead. Still, a multi-get might actually hit all 16 servers. >> >> That doesn't make sense. Why would you expect 16 servers acting in >> parallel to be slower than a single server? And in many/most cases >> the application will also be spread over multiple servers so the load >> is distributed independently there as well. > > Why not? Will it really be in parallel? Given that most application code is > fairly linear (i.e. all parallelism will have to come from the client > library). Even with true parallelism, you'll still have to connect to all > servers, be hindered by slow starts, etc (a connection pool may help here). Are you only expecting to run one client that only makes one query at once? > I'm just wondering whether the connection and other tcp/ip overheads will be > outweighed by any load-spreading gains. Especially since memcached's part of > the job is fairly quick. If you are facebook-size, you might want to convert to udp, but I thought that was more more of a number-of-client-connection issue for them from a bazillion preforked apache processes all connecting separately to the servers. -- Les Mikesell lesmikes...@gmail.com
Re: recommended maximum number of nodes in memcache cluster (server pool)
On Sun, Nov 27, 2011 at 10:58 AM, Arjen van der Meijden wrote: >> >> Are you only expecting to run one client that only makes one query at >> once? > > Obviously not. But the performance is mostly interesting from the > client-perspective, that's the one your users are waiting on. But which client? Usually if you need memcache to scale you will be running many clients in parallel - and if they are doing single-key operations in many cases adding more servers will make them completely separate. It is only multi-gets with many small keys that don't scale forever. > If you can > manage to send every user's request to only a few memcached-instances, > regardless of how many there are, than the server side is basically just > resource planning. > So in that regard, there isn't really an upper limit to the amount of > servers. But for practicality, you'll likely be limited by the amount of > connections the clients will have to maintain, to actually effectively use > memcached. Although with current client libraries and smart use of > memcached, that may well be in the high thousands. Yes, it is more a matter of using smart clients. But still, you are likely to have a problem with your backend persistent storage before you get to that point - especially if you expect to recover from any major failure that dumps most of your cache at once. -- Les Mikesell lesmikes...@gmail.com
Re: Best Architecture For DNS Round Robin + Memcached
On Fri, Feb 10, 2012 at 2:21 AM, Yiftach Shoolman wrote: > >> This makes absolutely no sense at all. If you have two servers and put a >> webserver and memcached on both, then *half* of all cache requests will be >> served by localhost and cause no network I/O, and half will go over the >> network. But if you put a webserver on one and memcached on the other, then >> *all* cache requests will be over the network, thus doubling the amount of >> network I/O for the same amount of web requests. > > > TIf you but the Memcached on a dedicated server each webserver only deals > with the network I/O associated with its traffic, leaving the dedicated > Memcached server to deal with all cached traffic. Normally you would have separate front/back end networks for web and internal traffic especially if you are scaling to a point where either might be saturated. There should be little conflict. > To clear it more, if you have N servers each deployed with a webservers a > memcached server, and memcached is distributed across all servers, each > webservers needs to deal with Memcached network I/O associated with N-1 > webservers --> we found it architecturally wrong, it actually slows down the > entire application If you have one memcached server and it goes down, you lose 100% of your caching. -- Les Mikesell lesmikes...@gmail.com
Re: Issue 256 in memcached: PLEASE do not remove cachedump, better dumping feature needed
On Sun, Feb 26, 2012 at 10:51 AM, Slawomir Pryczek wrote: > > Easiest thing would be probably just increase the LRU keys scanned to > eg. 10k but it'll probably just kill the server :) How do you analyze the data to decide what should be kept? Would it help to just use a shorter expire time on everything since it is being evicted anyway, then write back anything you are actively reusing to bump up the time to live? That way less active data gets out of the way sooner with no extra work. -- Les Mikesell lesmikes...@gmail.com
Re: Storage Engines?
On Thu, Jul 5, 2012 at 5:00 PM, Brian Moon wrote: > I have tried running cluster. It is not a simple system to run. It requires > a lot of hand holding. > So you want a multi-node db with replication that is as fast as a cache, simple to run, and doesn't have a company supporting it? I suppose you want it to be reliable too. -- Les Mikesell lesmikes...@gmail.com
Re: Storage Engines?
On Thu, Jul 5, 2012 at 7:01 PM, Brian Moon wrote: > I just want it all! Is that too much to ask! Expecting binary client support, not only in the language of your choice but packaged in the extension mode of your choice seems a little much... Is riak over http really a big problem for you? -- Les Mikesell lesmikes...@gmail.com
Re: Storage Engines?
On Fri, Jul 6, 2012 at 10:49 AM, Brian Moon wrote: > > Hmm, memcached has it. Redis has it. If you want your product to be used > seriously by the PHP community, that is the only way to go. Native PHP + > HTTP is just not an option. But the free product you want probably wouldn't have any reason to care if it is taken seriously or not... > HTTP is a horrible transport for speed. > Especially when implemented using cURL libs in PHP code. I need > sub-millisecond connect times and would prefer persistent connections. Riak > over HTTP does not give me either. I know the cURL overhead. Its 2ms just > for making the objects and creating the connections. I think riak is pedantically correct about http 1.1, so persistent connections should work fine. And if you need to the speed to assemble a lot of separate values, you might get the db to do that for you via link walking, secondary indexes, etc. -- Les Mikesell lesmikes...@gmail.com
Re: Open Source NoSQL ORM(ish)
On Mon, Jul 23, 2012 at 9:19 PM, Evan Buswell wrote: > > Lot's of examples in the docs. But yeah; maybe I should add a quick > complete example to the front page? I'll do this soon. Did I miss where you describe the language(s) it supports? -- Les Mikesell lesmikes...@gmail.com
Re: Volume memcached can handle
On Fri, Sep 21, 2012 at 12:55 PM, Howard Chu wrote: > An "in-memory database" would have the same limits as memcached - > both are limited to the size of physical RAM. But the main point of memcache is that it is designed to be spread over multiple servers. So you are only limited by the number of servers you want to throw into the pool. -- Les Mikesell lesmikes...@gmail.com
Re: Is it posible that two Seperate Instances of Memcache communicate with each other
On Tue, Oct 9, 2012 at 8:59 AM, Kiran Kumar wrote: > Thanks , let me explain my architecture more clearly > > you misunderstand how memcached works. It doesn't front-end the > database servers like you think it does. It works like this: > > Memcache1 Memcache2 > \ / >\ / > \ / > \ / > \ / >\ / > MySQL Master > MySQL Slave > > There is NO replication between Memcache1 and Memcache2 because they > do not cache the same data. Memcache1 caches 50% of the data and > Memcache2 caches the other 50% of the data. There is no data overlap > so no synchronization is necessary. > > If either memcached server fails, the application requesting the data > should "fall through" and hit the database server(s) directly. > > Do you understand now? That description is correct, but it doesn't explain why your 2 applications wouldn't work the way you want in this configuration or why you would want separate independent servers for each application. Being able to distribute the cache over multiple servers is the main reason people would use memcache. -- Les Mikesell lesmikes...@gmail.com
Re: Memcache : Two Seperate Memcache's instances in sync for a single application
On Thu, Oct 11, 2012 at 10:15 AM, Kiran Kumar wrote: > Thanks rspadim , it was a mistake from my end i have edited the question . > > One of the class in Application writes to both the instances of Memcache . It is still not clear why you need this. A more typical use of memcache would be to have enough members in a single cluster that the backend database can survive if you temporarily lose one or two of the cache members and some percentage of queries hit it directly. -- Les Mikesell lesmikes...@gmail.com
Re: Is the term Replication and clustering are different with respect to 2 instances of Memcache for the same application .
On Fri, Oct 12, 2012 at 9:18 AM, Kiran Kumar wrote:
> I have written a sample application as shown
>
> String location = "localhost:11211,122.34.5:11211";
> MemcachedClientBuilder builder = new
> XMemcachedClientBuilder(AddrUtil.getAddressMap(location));
> mcc.set("a", 0, "Hello,xmemcached");
>
>
> Now i have memcache installed on both the IP addresses defined above . and i
> observed that if the local host server is down , data is fetched from the
> 2nd defined server .
>
> Please let me know , is there any difference between the Clustering and
> Replication here ??
>
> And i see a lot of buzz on using Repcached with memcached for replication
> purpose , please let me know if i am missing something regarding the
> difference between clustering and memcache ??
>
> Being a newbie to memcache , Plese correct me if i am wrong .
First, note that memcache is intended to be used only as a cache in
front of a slower but reliable data store where on a cache miss, the
client will pull the data from the backend store and refresh it in the
cache. Memcache itself does not do any replication, although you may
see 3rd party tools that attempt to keep redundant copies of the data.
What is supposed to happen is that if a client notices that one of
the configured severs is down it will adjust its hashing to evenly
spread the keys over the remaining set. Then the first cache miss
will update it in the new still-working location so other than having
a smaller capacity and possibly evicting things sooner, things
continue normally. Alternatively you can use a hash computation that
doesn't change and just always fail on the portion of the keyspace
that the failing server handles until it comes back. With a large
number of memcache servers, this results in a small percentage of
requests always hitting the data store directly when a cache server is
down, but avoids the chance of inconsistency if the clients notice the
outage/recovery at slightly different times.
--
Les Mikesell
lesmikes...@gmail.com
Re: Is the term Replication and clustering are different with respect to 2 instances of Memcache for the same application .
On Fri, Oct 12, 2012 at 11:00 AM, Kiran Kumar wrote: > > Could you please check this link > https://groups.google.com/forum/#!topic/memcached/YCKNM6wRTbk where the > author is saying that if you maintain two instances of servers in the list , > the Data will be automatically backed up to the other server also , is > thisn't clustering ?? I don't see anything about data being 'backed up' in that link. It says that if you add a new server instance the clients will fill it in as the key hashing is adjusted to spread across the servers and they refresh cache misses as they pull them from the backend data store. They seem to be talking about running another memcached instance on the same server but a different port, but that doesn't make any difference to the client. -- Les Mikesell lesmikes...@gmail.com
Re: Is the term Replication and clustering are different with respect to 2 instances of Memcache for the same application .
On Fri, Oct 12, 2012 at 11:31 AM, Kiran Kumar wrote: > > Thanks LesMikesell you were right there is nothing mentioned anything > about data being backed up in that link . > What i really want to convery is that if one of the Memcahe Server one is > is down , then automatically Data is being obtained from Memcahe Server two > , which avoids single point of failure . so i don't care if Data is being > obtained from any of the defined servers . > > ( that is what i mean to say data being copied to other location , i > sincerely if it creates a different meaning in this context ) > > (becuase as a end user i don't bother from which the data is being > obtained ) Memcache should only be used for fast repeated access to _copies_ of data that can be reliably retrieved from some other database or storage. There are any number of reasons why a server will not have the data a client requests (it expired, it was evicted due to lack of space, the server was restarted, etc.). The client's response to a cache miss should always be to get the data from the reliable database and update it into the cache. So it won't matter if any particular data is lost for any particular reason as long as the backend database can keep up with the clients requesting the missed data (which they will then refresh into a rebalanced hash location).If you are planning to use memcache to store the only copy of data that you can't reconstruct, you should be looking for some other product. Memcache is just a very fast distributed cache, not a reliable database. But as long as you can retrieve the data for cache misses from some other source you can just add more servers to a cluster to scale to any size, and other than having to configure each client to know about all the servers it will take care of itself. -- Les Mikesell lesmikes...@gmail.com
Re: Is the term Replication and clustering are different with respect to 2 instances of Memcache for the same application .
On Fri, Oct 12, 2012 at 1:16 PM, Kiran Kumar wrote: > Thanks LesMikesell,for the great explanation , i am helpless here , i am > working on a existing application , which is designed in such a way that all > the Data is written to Memcache (and there is no Database at all ) which is > the only data store currently , so what i was asking is that, will > clustering of Memcache Servers will avoid single point of failure ?? It will not avoid losing the values currently in the cache. If that matters, memcache is not what you should be using to store it. Clustering avoids a single point of failure in the sense that the hash re-balancing continues to provide the clients a place to cache freshly obtained data. -- Les Mikesell lesmikes...@gmail.com
Re: Is the term Replication and clustering are different with respect to 2 instances of Memcache for the same application .
On Fri, Oct 12, 2012 at 2:03 PM, Kiran Kumar wrote: > Will replication of Memcache servers can solve the problem of not losing the > data ?? Not in an absolute sense. That is, there are still other reasons data might be evicted, and nothing in memcache is going to provide replication - it is just not what it is designed for. And if your whole site loses power, it will be gone anyway. Having said that, there are other people with the same problem. http://www.couchbase.com/couchbase-server/overview might work ( I haven't tried it, so that's not a recommendation - just something that looks like it will it will work with the same clients but attempts to provide reliable storage). There have been other similar attempts, but I haven't followed their current status. -- Les Mikesell lesmikes...@gmail.com
Re: Is the term Replication and clustering are different with respect to 2 instances of Memcache for the same application .
On Fri, Oct 12, 2012 at 2:50 PM, Kiran Kumar wrote: > Thanks LesMikesell , > > I was searching for Data replication Option with xMemcahced library , what i > found is that Data replication with xmemcache is possible by using repcached > , please see this link > > https://groups.google.com/forum/#!msg/xmemcached/4LezU1A7ldU/OpXD_uEHDgAJ > > and let me know is that dependable to go with ?? can i use repcache with > Memcache on Java application . > I don't know anything about repcached. It might work, but if you need reliable storage I'd recommend using something that is designed to provide reliable storage instead of just using something designed to be a cache even with multiple instances. -- Les Mikesell lesmikes...@gmail.com
Re: Questions about memcached in general and failover
On Tue, Oct 16, 2012 at 11:22 AM, Kiran Kumar wrote: > > Memcache doesn't automatically comes with Replication facility (High > Avialibility) , i recomend you to use Repcache Patch on top of your existing > mecached for obtaining Replication of data > within your servers . > > The only issue i see is that Repcached only works / Successfully Worked when > there are only two servers two replicate . If you are going to be stuck with this restriction - and have to build your own fail-over, is there any advantage to using memcache compared to redis with its much larger feature set? -- Les Mikesell lesmikes...@gmail.comi
Re: data synchronization betwean memcached cluster nodes?
On Wed, Oct 17, 2012 at 12:25 AM, Raymond Wang wrote: > I am newbie to Memcached, and I have a questions about cluster deployment: > > does memcached support data synchronization betwean cluster nodes? if it > does, how can I determine the scope of synchronization? No, the keys are distributed over the cluster nodes and if data is not found in the cache it is up to the client to pull a new copy from the persistent data store and refresh it in the cache. -- Les Mikesell lesmikes...@gmail.com
Re: Behavior of Memcached Client during Replication Process
On Wed, Oct 17, 2012 at 11:24 AM, Kiran Kumar wrote: > Hi , > > We are using Memcache in a different/wrong way , that is Memcache as a > Complete Data Store itself . > > The setup of our Application is in such a way that , there are two Memcache > servers (Server1 and Server2 )where both of them acting as active active > (Master - Master ) each of them gets unique store of Data , and finally > repcached is applied on top of these severs for providing replication . > > The Data is being replicated bethween these two servers and i observed that > there is a small delay regarding the two servers being in sync with each > other > > I am using Xmemcached 1.4 version as Memcache Client . > > I have these two questions with respect to the above set up of our > Application . > > 1. Is the XMemcached Client Smart enough to read Key from Server2 , > incase it can't find that key in Sever 1 ( As i mentioned that there is a > small delay till both the servers are in synch with each other ) > > 2. Incase i configure my Memcache client to use > KetamaMemcachedSessionLocator inside the code , will this be of any help > with respect to the above scenario ?? > There should be options for how the client handles a server failure: http://code.google.com/p/xmemcached/wiki/FailureMode_StandbyNode Failure doesn't mean 'key doesn't exist', though, it means 'server connection fails'. -- Les Mikesell lesmikes...@gmail.com
Re: Behavior of Memcached Client during Replication Process
On Wed, Oct 17, 2012 at 1:56 PM, Kiran Kumar wrote: > Les Mikesell , Thanks for the link , but unfortunately that is no where > related to my question above . > anyway once again , What i was asking is that as there is some delay in Data > Replication , will the Memcache Client checks server2 also in case if it > doesn't found in Server 1 . No, I can't imagine any circumstance where a memcache client would consider a key that doesn't exist in its expected location to be a server error. Why should it?I think the only way you can get that effect is to define only one server. All clients using the same hashing should store/retrieve it on the same target as the first choice anyway with the only reason to retry being if one is down - but that leaves you without a good way to handle the situation where the down instance is restarted and its cache is empty. -- Les Mikesell lesmikes...@gmail.com
Re: Memcached and repcached not replicating 2 master servers
On Mon, Oct 22, 2012 at 2:41 PM, Kiran Kumar wrote: > Hi , > > I have memcached-14.5 and -repcached-2.2 installed on memcached on ubuntu. > They install went great and when i start memcached i get: replication: > connect (peer=server1:11212) replication: marugoto copying replication: > close replication: listen This looks good and for testing purpose i set in a > Server 1 > > set my_key 0 2592000 1 > 5 > > and was able to get this in Server 2 . All this works fine . > > But my question / issue is that , when i set the Data through MemcacheClient > , the data is not being properly replicated (Means sometimes the Data is > reflected and sometimes not ) > > String location = server1:11211 server2:11211 > MemcachedClientBuilder builder = new > XMemcachedClientBuilder(AddrUtil.getAddressMap(location)); > builder.setSessionLocator(new KetamaMemcachedSessionLocator(true)); > > > Please let me know if i need to set anything more to make it work ?? If the memcache client knows about 2 servers it will send half to one and half to the other based on the key hashing. Does repcached replicate both directions? In any case this sounds like an issue with repcached so not something that most people on this list would know. -- Les Mikesell lesmikes...@gmail.com
Re: How to solve atomic operation issue within two instances of Memcache Servers
On Thu, Oct 25, 2012 at 5:38 AM, Henrik Schröder wrote: > No, you can't solve this problem as long as you keep insisting on your weird > setup. Yes, distributed locking for atomic operations is an extremely difficult problem to solve - perhaps not even possible to do correctly with just 2 hosts where you can't get a quorum if they lose network contact. > If you absolutely must have some sort of replicated datastore, memcached is > the wrong choice, you'd be much better off looking at *actual* replicated > datastores, such as HBase or MongoDB. Or, if you need to keep the memcache client, maybe couchbase would work on the server side: http://www.couchbase.com/membase -- Les Mikesell lesmikes...@gmail.com
Re: Stale data handling with memcached/consistent hashing
On Tue, Dec 25, 2012 at 5:03 AM, howard chen wrote: > >> Assuming you're doing some cloud use case where you're frequently >> adding/removing servers? Most memcached server lists should stay fairly >> static. > > > Yes, the server lists should be static most of the time, but we need to do > VMs housekeeping from time to time. We are looking for elegant way to handle > stale cache without the need of flush data every-time when we updated the > server lists. Can't you find a reasonable expire time that won't overload your backend data store and also won't go too long with old data? -- Les Mikesell lesmikes...@gmail.com
Re: DB support
On Tue, Sep 24, 2013 at 3:16 AM, Namita Nair wrote: > Hi All, > > I mean does the memcache automatically load the data if not found in the > cache through some configuration like the one present in the hazelcast and > oracle coherence. > It is up to the client to obtain/load the data when it is not already current in the cache. There may be some clients embedded in database or database-like packages, but in general your client can use any persistent data store along with memcache. -- Les Mikesell lesmikes...@gmail.com -- --- You received this message because you are subscribed to the Google Groups "memcached" group. To unsubscribe from this group and stop receiving emails from it, send an email to memcached+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
Re: Thousands of CLOSE_WAIT connections
On Mon, Sep 30, 2013 at 10:36 AM, Nic Jansma wrote: > ... > > The rest of the connections are in FIN_WAIT1, ESTABLISHED, etc, but the vast > majority are the ~4,000 CLOSE_WAIT connections. > > I'm going to try bumping up the connection limit to 32k to avoid this for > now, but clearly there's something going on where memcached isn't closing > connections. That sounds like your client is opening persistent connections but not reusing them. -- Les Mikesell lesmikes...@gmail.com -- --- You received this message because you are subscribed to the Google Groups "memcached" group. To unsubscribe from this group and stop receiving emails from it, send an email to memcached+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
Re: Thousands of CLOSE_WAIT connections
On Mon, Sep 30, 2013 at 11:44 AM, Nic Jansma wrote: > > On Monday, September 30, 2013 12:23:42 PM UTC-4, LesMikesell wrote: >> >> That sounds like your client is opening persistent connections but not >> reusing them. > > > Doesn't the CLOSE_WAIT state indicate that the client has sent a FIN and yet > memcached hasn't internally closed/cleaned up the connection? > > I don't fully understand how pecl memcache/memcached's persistent > connections feature uses the socket, but I don't imagine they would send a > FIN then still try to re-use the connection later. Yes, I guess I had it backwards. CLOSE_WAIT should mean the other end has sent the FIN and is done sending. The server still needs to send the requested data before closing its side - maybe the client isn't reading fast enough and the tcp window is full at this point. -- Les Mikesell lesmikes...@gmail.com -- --- You received this message because you are subscribed to the Google Groups "memcached" group. To unsubscribe from this group and stop receiving emails from it, send an email to memcached+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
Re: Thousands of CLOSE_WAIT connections
On Thu, Oct 3, 2013 at 4:50 PM, Nic Jansma wrote: > I don't think the problem is caused by the PHP extension at this point, > since having the sockets in a CLOSE_WAIT state is most likely indicative of > something in the memcached server not closing the connection after it gets a > FIN. > The send/receive sides of a socket are closed separately. The client's FIN means it isn't going to send any more. That's almost unrelated to the server having to finish sending the requested data before closing it's side. It can very well be that the client isn't reading the response it requested and your tcp window is full as the server tries to send. > I've been monitoring memcached over the past few days, and it normally > doesn't get in this state. i.e. I don't normally see ANY CLOSE_WAIT > connections open. > > However, when it starts not responding to connection requests, it appears to > be in this state where there's thousands of CLOSE_WAIT connections. You have a finite number of sockets. > Does anyone have suggestions for how I can debug this further? Memcached is > not being production-ready reliable for me right now (including the weekly > crash listed in the original post, which may or may not be related). Lots of people are using various versions of the server in production. Can you try to reproduce the behavior with some other client or benchmark/load test tool? My guess is that it is something unrelated in the code calling the client library that can cause it to request but not consume the response. -- Les Mikesell lesmikes...@gmail.com -- --- You received this message because you are subscribed to the Google Groups "memcached" group. To unsubscribe from this group and stop receiving emails from it, send an email to memcached+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
Re: Problems when one of the memcached server down
On Thu, Oct 17, 2013 at 1:08 AM, SivaRam M wrote: > > Apologies for intervening here. I'm using memcahce-php client and there is > this call called getstats() which returns stats of a server if it is up an > runnig > and returns false if there is something really bad happens to server. > My question is while hashing the key to a particular server . Will our > consistent hash function consider this failed server . > I just want to know what backup plans are available if a server is down. The backup plan should always be for the client to fetch the data from a persistent store on any cache miss. I may have this backwards, but I think the clients with consistent hashing will keep the same hash regardless of the server state and continue to have hash misses for whatever percentage of servers are down at any time. Ones that don't have consistent hashing will adjust the ring to the number of working servers, losing some current data but letting the clients update it in the new location on the first access. Obviously, the more servers you use the less the impact of losing one will be. -- Les Mikesell lesmikes...@gmail.com -- --- You received this message because you are subscribed to the Google Groups "memcached" group. To unsubscribe from this group and stop receiving emails from it, send an email to memcached+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
Re: Problem regards Storing files inside Memcached server?
On Thu, Oct 17, 2013 at 8:58 AM, sekhar mekala wrote:
> HI,
>
> I having an input file(.JSON,.jpg,.txt,etc..).That file i need to store into
> memcached server.
> I don't want to convert file to byte[] before passing to memcached server.
> If any possibility to store file inside Memcached server?
> I am using spymemcached tool.
>
> Example:
>
> MemcachedClient mc=new MemcachedClient(new
> InetSocketAddress("192.168.7.104",11211));
> File file=new File("D:\\test.txt");
> mc.set("Key1",3600,file);
> mc.get("Key1");
>
Memcache doesn't care about the content of what you set/get. If your
question is about the size, the default limit is 1MB so you either
need to chunk up the data for bigger files or use the -l option to
raise the size limit (which is allowed but perhaps not a good idea).
--
Les Mikesell
lesmikes...@gmail.com
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Re: Memcached cluster
On Mon, Mar 3, 2014 at 6:01 AM, Ranjit D'Souza wrote: > I have a basic question: > > Does memcached support clustering and HA out of the box, or does it need > some third party integration in order to do so? Yes, but it is a cache, not a persistent store so the way it handles failure of a node is for the client to fetch a new copy of the cache misses from the backing storage. -- Les Mikesell lesmikes...@gmail.com -- --- You received this message because you are subscribed to the Google Groups "memcached" group. To unsubscribe from this group and stop receiving emails from it, send an email to memcached+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
Re: Memcached cluster
On Mon, Mar 3, 2014 at 11:36 PM, Ranjit D'Souza wrote: > Thank you > > Is there any concept of master-slave configuration (like in Redis), and > promoting the slave to master? No, the server nodes are all alike and don't need to know about each other. The clients need to know about all the servers and they distribute the data by hashing the keys. Depending on the hashing scheme the clients can rebalance the distribution when a node fails (invalidating some existing data) or continue to fail and use the backing store for the missing percentage until the node is back on line. > Can you point me to a document or wiki link that gives more information on > how to set up a memcached cluster? The server side is packaged for some Linux distributions. You just configure the amount of memory for it to use on each node. -- Les Mikesell lesmikes...@gmail.com -- --- You received this message because you are subscribed to the Google Groups "memcached" group. To unsubscribe from this group and stop receiving emails from it, send an email to memcached+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
Re: Memcached cluster
On Tue, Mar 4, 2014 at 2:56 AM, Ranjit D'Souza wrote: > > Thanks guys, this is quite helpful > > In the same vein, can we also say that memcache replication is also a client > side driven solution? In the stock system, there is no replication - although I believe others done it with client code. If you have a large enough number of servers, losing one will just add a small percentage of extra load on your backend DB to cover the extra cache misses. -- Les Mikesell lesmikes...@gmail.com -- --- You received this message because you are subscribed to the Google Groups "memcached" group. To unsubscribe from this group and stop receiving emails from it, send an email to memcached+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
Re: Idea for reclaimation algo
On Fri, Apr 11, 2014 at 3:47 AM, Slawomir Pryczek wrote: > > When using memcached as a buffer for mysql writes, we know exactly what to > hit and when. Short TTL expired items, pile up near the head... long TTL > "live" items pile up near the tail and it's creating a barrier that prevents > the LRU algo to reclaim almost anything, if im getting how it currently > works, correctly... Are you saying that within the same slab, non-expired items are evicted instead of available expired items? Are you sure you aren't just targeting different slabs because of the item size? -- Les Mikesell lesmikes...@gmail.com -- --- You received this message because you are subscribed to the Google Groups "memcached" group. To unsubscribe from this group and stop receiving emails from it, send an email to memcached+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
