nice. On Mar 8, 2011, at 1:14 PM, Eric Day wrote:
> Hi Curtis, > > On Tue, Mar 08, 2011 at 04:31:59PM +0000, Curtis Carter wrote: >> Couple of questions. >> Where did you come up with 300 bytes per message for ets? > > Raw message = key(16) + ttl(8) + hide(8) + body(100) = 132 bytes > > I inserted the raw message data as the tuple {key/binary, ttl/integer, > hide/integer, body/binary} in ets (5 million) and inspected the > memory usage. It lines up with what should be used with the given > type overheads in: > > http://www.erlang.org/doc/efficiency_guide/advanced.html#id66654 > > It was very fast, but it did come with that overhead. > > As far as queue storage, we won't be using a traditional queue > structure alone. We need a few other indexes into the data store for > efficient operations, not just inspecting beginning of the queue. For > example, TTL and hide properties require timestamp-based indexes into > the queue as well, which are probably best done with a secondary heap > index or btree. We'll also need insert order and message ID indexed. > >> When you say 2 threads for Erlang what do you mean? Do you mean 2 >> schedulers and/or 2 run queues, Erlang processes, or Erlang vms. > > Sorry, two scheduler threads in one vm (os kernel threads). For C++ > this was also 2 threads with PTHREAD_SCOPE_SYSTEM. The main point > is that all connections (erlang processes, eventlet green threads, > state structures in C++ event loop) were running on two cores. For > Python this was just a os.fork() after creating the listening socket. > >> I wrote a basic queue using the queue module(double ended FIFO) that was >> handling around 526k a second with 100 clients on an old core2 duo laptop. >> 200000 8 byte messages per client (I do not know how the queue module is >> implemented) >> 100 clients/queues >> Was very unscientific in the front seat of my car while waiting on someone. >> NO HTTP > > The main thing I was trying to test was language overhead, especially > with HTTP parsing. For the raw echo test, erlang and python are pretty > even. Python WSGI does have some overhead (just as Erlang modules > like webmachine did), but that may be solved with an implementation > optimization (like I did by not using webmachine). > >> I know very apple/oranges here. From what I've seen in the past Erlang does >> not pass other http servers until you hit a large amount of concurrent >> requests. > See: http://oddments.org/?p=494 > > Eventlet came in a bit behind C++ for the larger payload (512k data > for each of the 32k connections), but it held up quite well. Eventlet > was only running with a single process too, so I imagine with two > processes the time would improve. In a later test I used Erlang and > it came in between the C++ 2-thread test and Eventlet single thread > (as you would expect from my other tests). > > -Eric > >> On Mar 7, 2011, at 3:32 PM, Eric Day wrote: >> >>> I ran the tests again to verify: >>> >>> 500k requests - 10 processes each running 50k requests. >>> >>> time req/s cs us sy id >>> 2 thread/proc >>> echo c++ 7.19 69541 142182 23 77 0 >>> echo erlang 9.53 52465 105871 39 61 0 >>> echo python 9.58 52192 108420 42 58 0 >>> 2 thread/proc >>> wsgi python 58.74 8512 18132 86 14 0 >>> webob python 78.75 6349 13678 89 11 0 >>> webmachine* 63.50 7874 11834 89 11 0 >>> openstack 20.48 24414 49897 68 32 0 >>> >>> cs/us/sys/id are from vmstat while running the tests. >>> >>> * webmachine degrades over time with long-lived, multi-request >>> connections. This number was estimated with 1000 requests per >>> connection. At 50k requests per connection, the rate dropped to >>> 2582 req/s. >>> >>> As you can see I was able to reproduce the same numbers. If >>> anyone would like to do the same, you can grab lp:burrow for the >>> "openstack" Erlang application (compile and run ./start), webmachine >>> is at https://github.com/basho/webmachine (you need to create a demo >>> app and make sure you set nodelay for the socket options), and I've >>> attached the python server and client (start 10 client processes when >>> testing). Find me on irc (eday in #openstack) if you have questions. >>> >>> If we hit performance issues with this type of application, we'll >>> probably hit them around the same time with both Erlang and Python >>> (then we'll look to C/C++). Since most OpenStack developers are a lot >>> more comfortable with Python, I suggest we make the switch. Please >>> response with thoughts on this. I'll add a sqlite backend to the >>> Python prototype and run some performance tests against that to see >>> if any red flags come up. >>> >>> -Eric >>> >>> On Sat, Mar 05, 2011 at 10:39:18PM -0700, ksan...@doubleclix.net wrote: >>>> Eric, >>>> Thanks for your experimentation and analysis. Somewhat illustrates the >>>> point about premature optimization. First cut, have to agree with you and >>>> conclude that python implementation is effective, overall. As you said,if >>>> we find performance bottlenecks, especially as the payload size increases >>>> (as well as if we require any complex processing at the http server layer) >>>> we can optimize specific areas. >>>> Just for sure, might be better for someone else to recheck. That way >>>> we have done our due diligence. >>>> Cheers >>>> <k/> >>>> >>>> -------- Original Message -------- >>>> Subject: [Openstack] Queue Service Implementation Thoughts >>>> From: Eric Day <e...@oddments.org> >>>> Date: Sat, March 05, 2011 4:07 pm >>>> To: openstack@lists.launchpad.net >>>> >>>> Hi everyone, >>>> >>>> When deciding to move forward with Erlang, I first tried out the Erlang >>>> REST framework webmachine (it is built on top of mochiweb and used >>>> by projects like Riak). After some performance testing, I decided to >>>> write a simple wrapper over the HTTP packet parsing built into Erlang >>>> (also used by mochiweb/webmachine) to see if I could make things a >>>> bit more efficient. Here are the results: >>>> >>>> Erlang (2 threads) >>>> echo - 58823 reqs/sec >>>> webmachine - 7782 reqs/sec >>>> openstack - 24154 reqs/sec >>>> >>>> The test consists of four concurrent connections focused on packet >>>> parsing speed and framework overhead. A simple echo test was also >>>> done for a baseline (no parsing, just a simple recv/send loop). As >>>> you can see, the simple request/response wrapper I wrote did get some >>>> gains, although it's a little more hands-on to use (looks more like >>>> wsgi+webob in python). >>>> >>>> I decided to run the same tests against Python just for comparison. I >>>> ran echo, wsgi, and wsgi+webob decorators all using eventlet. I ran >>>> both single process and two process in order to compare with Erlang >>>> which was running with two threads. >>>> >>>> Python (eventlet) >>>> echo (1 proc) - 17857 reqs/sec >>>> echo (2 proc) - 52631 reqs/sec >>>> wsgi (1 proc) - 4859 reqs/sec >>>> wsgi (2 proc) - 8695 reqs/sec >>>> wsgi webob (1 proc) - 3430 reqs/sec >>>> wsgi webob (2 proc) - 6142 reqs/sec >>>> >>>> As you can see, the two process Python echo server was not too far >>>> behind the two thread Erlang echo server. The wsgi overhead was >>>> significant, especially with the webob decorators/objects. It was >>>> still on par with webmachine, but a factor of three less than my >>>> simple request/response wrapper. >>>> >>>> A multi-process python server does have the drawback of not being >>>> able to share resources between processes unless incurring the >>>> overhead of IPC. When thinking about a horizontally scalable service, >>>> where scaling-out is much more important than scaling-up, I think >>>> this becomes much less of a factor. Regardless of language choice, >>>> we will need a proxy to efficiently hash to a set of queue servers in >>>> any large deployment (or the clients will hash), but if that set is a >>>> larger number of single-process python servers (some running on the >>>> same machine) instead of a smaller number of multi-threaded Erlang >>>> servers, I don't think it will make too much of a difference (each >>>> proxy server will need to maintain more connections). In previous >>>> queue service threads I was much more concerned about this and was >>>> leaning away from Python, but I think I may be coming around. >>>> >>>> Another aspect I took a look at is options for message storage. For >>>> the fast, in-memory, unreliable queue type, here are some numbers >>>> for options in Python and Erlang: >>>> >>>> Raw message = key(16) + ttl(8) + hide(8) + body(100) = 132 bytes >>>> Python list/dict - 248 bytes/msg (88% overhead) >>>> Python sqlite3 - 168 bytes/msg (27% overhead) >>>> Erlang ets - 300 bytes/msg (127% overhead) >>>> >>>> The example raw message has no surrounding data structure, so it is >>>> obviously never possible to get down to 132 bytes. As the body grows, >>>> the overhead becomes less significant since they all grow the same >>>> amount. The best Python option is probably an in-memory sqlite table, >>>> which is also an option for disk-based storage as well. >>>> >>>> For Erlang, ets is really the only efficient in-memory option (mnesia >>>> is built on ets if you're thinking of that), and also has a disk >>>> counterpart called dets. The overhead was definitely more than I was >>>> expecting and is less memory efficient than both Python options. >>>> >>>> As we start looking at other stores to use, there are certainly more >>>> DB drivers available for Python than Erlang (due to the fact that >>>> Python is more popular). We'll want to push most of the heavy lifting >>>> to the pluggable databases, which makes the binding language less of >>>> a concern as well. >>>> >>>> So, in conclusion, and going against my previous opinion, I'm starting >>>> to feel that the performance gains of Erlang are really not that >>>> significant compared to Python for this style of application. If >>>> we're talking about a factor of three (and possibly less if we can >>>> optimize the wsgi driver or not use wsgi), and consider the database >>>> driver options for queue storage, Python doesn't look so bad. We'll >>>> certainly have more of a developer community too. >>>> >>>> We may still need to write parts in C/C++ if limits can't be overcome, >>>> but that would probably be the case for Erlang or Python. >>>> >>>> What do folks think? >>>> >>>> -Eric >>>> >>>> _______________________________________________ >>>> Mailing list: https://launchpad.net/~openstack >>>> Post to : openstack@lists.launchpad.net >>>> Unsubscribe : https://launchpad.net/~openstack >>>> More help : https://help.launchpad.net/ListHelp >>> <speed_client.py><speed_server.py>_______________________________________________ >>> Mailing list: https://launchpad.net/~openstack >>> Post to : openstack@lists.launchpad.net >>> Unsubscribe : https://launchpad.net/~openstack >>> More help : https://help.launchpad.net/ListHelp >> >> >> >> Confidentiality Notice: This e-mail message (including any attached or >> embedded documents) is intended for the exclusive and confidential use of the >> individual or entity to which this message is addressed, and unless otherwise >> expressly indicated, is confidential and privileged information of Rackspace. >> Any dissemination, distribution or copying of the enclosed material is >> prohibited. >> If you receive this transmission in error, please notify us immediately by >> e-mail >> at ab...@rackspace.com, and delete the original message. >> Your cooperation is appreciated. 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