bq: Will TLOG replicas use less network bandwidth? No, probably more bandwidth. TLOG replicas work like this: 1> the raw docs are forwarded 2> the old-style master/slave replication is used
So what you do save is CPU processing on the TLOG replica in exchange for increased bandwidth. Since the only thing forwarded in NRT replicas (outside of recovery) is the raw documents, I expect that TLOG replicas would _increase_ network usage. The deal is that TLOG replicas can take over leadership if the leader goes down so they must have an up-to-date-after-last-index-sync set of tlogs. At least that's my current understanding... Best, Erick On Fri, Dec 8, 2017 at 12:01 PM, Joe Obernberger <joseph.obernber...@gmail.com> wrote: > Anyone have any thoughts on this? Will TLOG replicas use less network > bandwidth? > > -Joe > > > On 12/4/2017 12:54 PM, Joe Obernberger wrote: >> >> Hi All - this same problem happened again, and I think I partially >> understand what is going on. The part I don't know is what caused any of >> the replicas to go into full recovery in the first place, but once they do, >> they cause network interfaces on servers to go fully utilized in both in/out >> directions. It appears that when a solr replica needs to recover, it calls >> on the leader for all the data. In HDFS, the data from the leader's point >> of view goes: >> >> HDFS --> Solr Leader Process -->Network--> Replica Solr Process -->HDFS >> >> Do I have this correct? That poor network in the middle becomes a >> bottleneck and causes other replicas to go into recovery, which causes more >> network traffic. Perhaps going to TLOG replicas with 7.1 would be better >> with HDFS? Would it be possible for the leader to send a message to the >> replica to instead get the data straight from HDFS instead of going from one >> solr process to another? HDFS would better be able to use the cluster since >> each block has 3x replicas. Perhaps there is a better way to handle >> replicas with a shared file system. >> >> Our current plan to fix the issue is to go to Solr 7.1.0 and use TLOG. >> Good idea? Thank you! >> >> -Joe >> >> >> On 11/22/2017 8:17 PM, Erick Erickson wrote: >>> >>> Hmm. This is quite possible. Any time things take "too long" it can be >>> a problem. For instance, if the leader sends docs to a replica and >>> the request times out, the leader throws the follower into "Leader >>> Initiated Recovery". The smoking gun here is that there are no errors >>> on the follower, just the notification that the leader put it into >>> recovery. >>> >>> There are other variations on the theme, it all boils down to when >>> communications fall apart replicas go into recovery..... >>> >>> Best, >>> Erick >>> >>> On Wed, Nov 22, 2017 at 11:02 AM, Joe Obernberger >>> <joseph.obernber...@gmail.com> wrote: >>>> >>>> Hi Shawn - thank you for your reply. The index is 29.9TBytes as reported >>>> by: >>>> hadoop fs -du -s -h /solr6.6.0 >>>> 29.9 T 89.9 T /solr6.6.0 >>>> >>>> The 89.9TBytes is due to HDFS having 3x replication. There are about >>>> 1.1 >>>> billion documents indexed and we index about 2.5 million documents per >>>> day. >>>> Assuming an even distribution, each node is handling about 680GBytes of >>>> index. So our cache size is 1.4%. Perhaps 'relatively small block >>>> cache' >>>> was an understatement! This is why we split the largest collection into >>>> two, >>>> where one is data going back 30 days, and the other is all the data. >>>> Most >>>> of our searches are not longer than 30 days back. The 30 day index is >>>> 2.6TBytes total. I don't know how the HDFS block cache splits between >>>> collections, but the 30 day index performs acceptable for our specific >>>> application. >>>> >>>> If we wanted to cache 50% of the index, each of our 45 nodes would need >>>> a >>>> block cache of about 350GBytes. I'm accepting offers of DIMMs! >>>> >>>> What I believe caused our 'recovery, fail, retry loop' was one of our >>>> servers died. This caused HDFS to start to replicate blocks across the >>>> cluster and produced a lot of network activity. When this happened, I >>>> believe there was high network contention for specific nodes in the >>>> cluster >>>> and their network interfaces became pegged and requests for HDFS blocks >>>> timed out. When that happened, SolrCloud went into recovery which >>>> caused >>>> more network traffic. Fun stuff. >>>> >>>> -Joe >>>> >>>> >>>> On 11/22/2017 11:44 AM, Shawn Heisey wrote: >>>>> >>>>> On 11/22/2017 6:44 AM, Joe Obernberger wrote: >>>>>> >>>>>> Right now, we have a relatively small block cache due to the >>>>>> requirements that the servers run other software. We tried to find >>>>>> the best balance between block cache size, and RAM for programs, while >>>>>> still giving enough for local FS cache. This came out to be 84 128M >>>>>> blocks - or about 10G for the cache per node (45 nodes total). >>>>> >>>>> How much data is being handled on a server with 10GB allocated for >>>>> caching HDFS data? >>>>> >>>>> The first message in this thread says the index size is 31TB, which is >>>>> *enormous*. You have also said that the index takes 93TB of disk >>>>> space. If the data is distributed somewhat evenly, then the answer to >>>>> my question would be that each of those 45 Solr servers would be >>>>> handling over 2TB of data. A 10GB cache is *nothing* compared to 2TB. >>>>> >>>>> When index data that Solr needs to access for an operation is not in >>>>> the >>>>> cache and Solr must actually wait for disk and/or network I/O, the >>>>> resulting performance usually isn't very good. In most cases you don't >>>>> need to have enough memory to fully cache the index data ... but less >>>>> than half a percent is not going to be enough. >>>>> >>>>> Thanks, >>>>> Shawn >>>>> >>>>> >>>>> --- >>>>> This email has been checked for viruses by AVG. >>>>> http://www.avg.com >>>>> >> >
