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From "Mark Miller (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-3274) ZooKeeper related SolrCloud problems
Date Mon, 26 Mar 2012 14:02:28 GMT

    [ https://issues.apache.org/jira/browse/SOLR-3274?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13238404#comment-13238404
] 

Mark Miller commented on SOLR-3274:
-----------------------------------

bq. Can all the exception be explained by "connection loss between solr and zookeeper"?

bq. SessionExpiredException

This indicates the connection with ZooKeeper was lost.

bq. org.apache.solr.common.SolrException: Cannot talk to ZooKeeper - Updates are disabled.

If there is no connection to ZooKeeper, you will see this if you send an update.

bq. org.apache.solr.common.SolrException: no servers hosting shard: 

Sami Siren has a JIRA issue about improving this message I believe - but normally it means
that the cluster does not see a single node hosting a given shard. Not sure if this is related
to the above - not the same smoking gun.

bq. Can you point me in the direction of how to set it manually?

The default is only 10 seconds. I'd try 30 seconds perhaps? You don't want it too low, but
you also don't want it too high if you can help it. I can't remember what the "zookeeper"
default is, but I've seen it set as high as 60 seconds looking around some hbase usage...

You should be able to set it in solr.xml as a cores attribute: zkClientTimeout="30000" or
whatever.

That is:   <cores adminPath="/admin/cores" zkClientTimeout="30000"

You'd want to do it for each node.
                
> 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
>         Environment: Any
>            Reporter: Per Steffensen
>            Assignee: Mark Miller
>
> 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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