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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Created: (SOLR-2342) Lock starvation can cause commit to never run when many clients are adding docs
Date Tue, 01 Feb 2011 21:58:28 GMT
Lock starvation can cause commit to never run when many clients are adding docs
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                 Key: SOLR-2342
                 URL: https://issues.apache.org/jira/browse/SOLR-2342
             Project: Solr
          Issue Type: Bug
          Components: update
            Reporter: Michael McCandless
            Priority: Minor


I have a stress test, where 100 clients add 100 1MB docs and then call commit in the end.
 It's a falldown test (try to make Solr fall down) and nowhere near "actual" usage.

But, after some initial commits that succeed, I'm seeing later commits always time out (client
side timeout @ 10 minutes).  Watching Solr's logging, no commit ever runs.

Looking at the stack traces in the threads, this is not deadlock: the add/update calls are
running, and new segments are being flushed to the index.

Digging in the code a bit, we use ReentrantReadWriteLock, with add/update acquiring the readLock
and commit acquiring the writeLock.  But, according to the jdocs, the writeLock isn't given
any priority over the readLock (unless you set fairness, which we don't).  So I think this
explains the starvation?

However, this is not a real world use case (most apps would/should call commit less often,
and from on client).  Also, we could set fairness, but it seems to have some performance penalty,
and I'm not sure we should penalize the "normal" case for this unusual one.  EG see here (thanks
Mark): http://www.javaspecialists.eu/archive/Issue165.html.

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