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From "Ishan Chattopadhyaya (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-8687) Race condition with RTGs during soft commit
Date Wed, 17 Feb 2016 19:58:18 GMT

    [ https://issues.apache.org/jira/browse/SOLR-8687?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15151059#comment-15151059
] 

Ishan Chattopadhyaya commented on SOLR-8687:
--------------------------------------------

My stress test is here:
https://github.com/chatman/lucene-solr/blob/627b9ac9b46796f20be78b04ebbdfa4299b96ab7/solr/core/src/test/org/apache/solr/cloud/TestStressInPlaceUpdates.java

> Race condition with RTGs during soft commit
> -------------------------------------------
>
>                 Key: SOLR-8687
>                 URL: https://issues.apache.org/jira/browse/SOLR-8687
>             Project: Solr
>          Issue Type: Bug
>            Reporter: Ishan Chattopadhyaya
>
> I am facing a problem with stress testing SOLR-5944, even though I think this problem
persists in Solr even without my changes.
> The symptom is that during a stress test (similar to TestStressReorder), RTG gets a document
which is older version than that of the last acknowledged write.
> Possible reason:
> {code}
> (DUH2's commit())
> ...
> 1:      if (cmd.softCommit) {
> 2:        // ulog.preSoftCommit();
> 3:        synchronized (solrCoreState.getUpdateLock()) {
> 4:          if (ulog != null) ulog.preSoftCommit(cmd);
> 5:          core.getSearcher(true, false, waitSearcher, true);
> 6:          if (ulog != null) ulog.postSoftCommit(cmd);
> 7:        }
> 8:        callPostSoftCommitCallbacks();
> 9:      }
> ...
> {code}
> * Before line 1, there was an update (say id=2) which was in ulog's map. Maps are, say,
`map={2=LogPtr(1234)}, prevMap={...}, prevMap2={...}`
> * Due to line 4 (ulog.preSoftCommit()), the maps were rotated. Now, the id=2 is in prevMap:
`map={}, prevMap={2=LogPtr(1234)}, prevMap2={...}`. Till now RTG for id=2 will work.
> * Due to line 5, a new searcher is due to be opened. But this is asynchronous, and lets
assume this doesn't complete before few more lines are executed.
> * Due to line 6 (ulog.postSoftCommit()), the previous maps are cleared out. Now the maps
are: `map={}, prevMap=null, prevMap2=null`
> * If there's an RTG for id=2, it will not work from the ulog's maps, so it will fall
through to be searched using the last searcher. But, the searcher due to be opened in line
5 hasn't yet been opened. In this case, the returned document will be whatever version of
id=2 that was present in the previous searcher.
> Can someone please confirm if this is a potential problem? If so, any suggestions for
a fix, please? I tried opening a ulog.openRealtimeSearcher() in the above synchronized block,
but the problem still persists, but I haven't looked into why that could be.



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