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https://issues.apache.org/jira/browse/SOLR-3274?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14094033#comment-14094033
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Per Steffensen commented on SOLR-3274:
--------------------------------------
bq. Both nodes have 16 CPU cores, 48G of memory and RAID 10 (SSD), I thought it
would be hard to get performance issues there
Yes that should be hard. Well done! :-)
bq. Anyway, adding a separate node with 4th zookeeper instance might help,
right?
A ZK cluster should always have an uneven number of nodes. So if you want to
add additional ZK instances you should add two. I would rather move the two ZK
instances running on Solr-machines to two machines not running Solr. So that
you end up with 3 ZK instances where non of them run on machines also running
Solr. We never run ZK on the same machines as Solr - we have bad experiences
with that - loosing ZK connections all the time. You will still occasionally
loose ZK connections from Solrs when they are under high load, but usually they
reconnect fairly quickly (before session timeout) and you can continue
immediately.
I have been working on an optimized ZK where you do not loose ZK connections
nearly as often, but currently it is not prioritized to finish the job.
> ZooKeeper related SolrCloud problems
> ------------------------------------
>
> Key: SOLR-3274
> URL: https://issues.apache.org/jira/browse/SOLR-3274
> Project: Solr
> Issue Type: Bug
> Components: SolrCloud
> Affects Versions: 4.0-ALPHA
> Environment: Any
> Reporter: Per Steffensen
>
> Same setup as in SOLR-3273. Well if I have to tell the entire truth we have 7
> Solr servers, running 28 slices of the same collection (collA) - all slices
> have one replica (two shards all in all - leader + replica) - 56 cores all in
> all (8 shards on each solr instance). But anyways...
> Besides the problem reported in SOLR-3273, the system seems to run fine under
> high load for several hours, but eventually errors like the ones shown below
> start to occur. I might be wrong, but they all seem to indicate some kind of
> unstability in the collaboration between Solr and ZooKeeper. I have to say
> that I havnt been there to check ZooKeeper "at the moment where those
> exception occur", but basically I dont believe the exceptions occur because
> ZooKeeper is not running stable - at least when I go and check ZooKeeper
> through other "channels" (e.g. my eclipse ZK plugin) it is always accepting
> my connection and generally seems to be doing fine.
> Exception 1) Often the first error we see in solr.log is something like this
> {code}
> Mar 22, 2012 5:06:43 AM org.apache.solr.common.SolrException log
> SEVERE: org.apache.solr.common.SolrException: Cannot talk to ZooKeeper -
> Updates are disabled.
> at
> org.apache.solr.update.processor.DistributedUpdateProcessor.zkCheck(DistributedUpdateProcessor.java:678)
> at
> org.apache.solr.update.processor.DistributedUpdateProcessor.processAdd(DistributedUpdateProcessor.java:250)
> at org.apache.solr.handler.XMLLoader.processUpdate(XMLLoader.java:140)
> at org.apache.solr.handler.XMLLoader.load(XMLLoader.java:80)
> at
> org.apache.solr.handler.ContentStreamHandlerBase.handleRequestBody(ContentStreamHandlerBase.java:59)
> at
> org.apache.solr.handler.RequestHandlerBase.handleRequest(RequestHandlerBase.java:129)
> at org.apache.solr.core.SolrCore.execute(SolrCore.java:1540)
> at
> org.apache.solr.servlet.SolrDispatchFilter.execute(SolrDispatchFilter.java:407)
> at
> org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:256)
> at
> org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1212)
> at
> org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:399)
> at
> org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
> at
> org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
> at
> org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:766)
> at
> org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:450)
> at
> org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
> at
> org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
> at
> org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
> at org.mortbay.jetty.Server.handle(Server.java:326)
> at
> org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
> at
> org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:945)
> at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
> at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
> at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
> at
> org.mortbay.jetty.bio.SocketConnector$Connection.run(SocketConnector.java:228)
> at
> org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
> {code}
> I believe this error basically occurs because SolrZkClient.isConnected
> reports false, which means that its internal "keeper.getState" does not
> return ZooKeeper.States.CONNECTED. Im pretty sure that it has been CONNECTED
> for a long time, since this error starts occuring after several hours of
> processing without this problem showing. But why is it suddenly not connected
> anymore?!
> Exception 2) We also see errors like the following, and if Im not mistaken,
> they start occuring shortly after "Exception 1)" (above) shows for the fist
> time
> {code}
> Mar 22, 2012 5:07:26 AM org.apache.solr.common.SolrException log
> SEVERE: org.apache.solr.common.SolrException: no servers hosting shard:
> at
> org.apache.solr.handler.component.HttpShardHandler$1.call(HttpShardHandler.java:149)
> at
> org.apache.solr.handler.component.HttpShardHandler$1.call(HttpShardHandler.java:123)
> at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
> at java.util.concurrent.FutureTask.run(FutureTask.java:138)
> at
> java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
> at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
> at java.util.concurrent.FutureTask.run(FutureTask.java:138)
> at
> java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
> at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
> at java.lang.Thread.run(Thread.java:662)
> {code}
> Please note that the exception says "no servers hosting shard: <blank>".
> Looking at the code a "shard"-string was actually supposed to be written at
> <blank>. Basically this means that HttpShardHandler.submit was called with
> an empty "shard"-string parameter. But who does this?
> CoreAdminHandler.handleDistribUrlAction or SearchHandler.handleRequestBody or
> SyncStrategy or PeerSync or... I dont know, and maybe it is not that
> relevant, because I guess they all get the "shard"-string from ZooKeeper.
> Again something pointing in the direction of unstable collaboration between
> Solr and ZooKeeper.
> Exception 3) We also see exceptions like this
> {code}
> Mar 25, 2012 3:05:38 PM org.apache.solr.common.cloud.ZkStateReader$3 process
> WARNING: ZooKeeper watch triggered, but Solr cannot talk to ZK
> Mar 25, 2012 3:05:38 PM org.apache.solr.cloud.LeaderElector$1 process
> WARNING:
> org.apache.zookeeper.KeeperException$SessionExpiredException: KeeperErrorCode
> = Session expired for /collections/collA/leader_elect/slice26/election
> at
> org.apache.zookeeper.KeeperException.create(KeeperException.java:118)
> at
> org.apache.zookeeper.KeeperException.create(KeeperException.java:42)
> at org.apache.zookeeper.ZooKeeper.getChildren(ZooKeeper.java:1249)
> at
> org.apache.solr.common.cloud.SolrZkClient$6.execute(SolrZkClient.java:266)
> at
> org.apache.solr.common.cloud.SolrZkClient$6.execute(SolrZkClient.java:263)
> at
> org.apache.solr.common.cloud.ZkCmdExecutor.retryOperation(ZkCmdExecutor.java:65)
> at
> org.apache.solr.common.cloud.SolrZkClient.getChildren(SolrZkClient.java:263)
> at
> org.apache.solr.cloud.LeaderElector.checkIfIamLeader(LeaderElector.java:92)
> at
> org.apache.solr.cloud.LeaderElector.access$000(LeaderElector.java:57)
> at
> org.apache.solr.cloud.LeaderElector$1.process(LeaderElector.java:121)
> at
> org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:531)
> at
> org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:507)
> {code}
> Maybe this will we usable for some bug-fixing or for making the code more
> stable. I know 4.0 is not stable/released yet, and that we therefore should
> expect this kind of errors at the moment. So this is not negative criticism -
> just reporting of issues observed when using SolrCloud features under high
> load for several days. Any feedback is more than welcome.
> Regards, Per Steffensen
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