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https://issues.apache.org/jira/browse/SOLR-8687?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15153413#comment-15153413
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Yonik Seeley commented on SOLR-8687:
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Hmmm, RTG should be air-tight (I always hate changes to synchronization in this
area because it's hard to re-validate). We have stress tests for this, so it's
also disconcerting if it's not air-tight and our tests don't catch it.
I'll review the related code again...
> 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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