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https://issues.apache.org/jira/browse/OAK-2815?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14516618#comment-14516618
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Michael Marth commented on OAK-2815:
------------------------------------
[~tmueller], would it be able to simply skip adding elements to the cache while
the compaction is running? So that commits are not blocked. Would lead to some
cache misses later, but might be a decent compromise. WDYT?
> Persistent cache may block commit
> ---------------------------------
>
> Key: OAK-2815
> URL: https://issues.apache.org/jira/browse/OAK-2815
> Project: Jackrabbit Oak
> Issue Type: Bug
> Affects Versions: 1.2
> Reporter: Marcel Reutegger
> Assignee: Thomas Mueller
> Fix For: 1.3.0, 1.2.2, 1.0.14
>
> Attachments: OAK-2815.patch
>
>
> The persistent cache may block a commit for a rather long time if the
> generation is switched during the commit. The default configuration tells the
> persistent cache to compact the store when it is closed. This is exactly what
> happens when a generation is switched.
> I think it would be best to disable compaction.
> I was able to reproduce it with the {{ContinuousRevisionGCTest}} in oak-run
> with {{-DgarbageRatio=0.9}}, but it probably also happens with the default
> garbage ratio of 0.5.
> Once the MVStore reaches 1GB, the console will show something like this:
> {noformat}
> Performed RevisionGC in 6.331 s
> (VersionGCStats{ignoredGCDueToCheckPoint=false, deletedDocGCCount=54054,
> splitDocGCCount=0, intermediateSplitDocGCCount=0,
> timeToCollectDeletedDocs=622.8 ms, timeTakenToDeleteDocs=5.708 s})
> .................
> Performed RevisionGC in 9.232 s
> (VersionGCStats{ignoredGCDueToCheckPoint=false, deletedDocGCCount=26026,
> splitDocGCCount=0, intermediateSplitDocGCCount=0,
> timeToCollectDeletedDocs=6.549 s, timeTakenToDeleteDocs=2.682 s})
> Performed RevisionGC in 1.269 s
> (VersionGCStats{ignoredGCDueToCheckPoint=false, deletedDocGCCount=12012,
> splitDocGCCount=0, intermediateSplitDocGCCount=0,
> timeToCollectDeletedDocs=133.5 ms, timeTakenToDeleteDocs=1.134 s})
> Performed RevisionGC in 20.49 ms
> (VersionGCStats{ignoredGCDueToCheckPoint=false, deletedDocGCCount=0,
> splitDocGCCount=0, intermediateSplitDocGCCount=0,
> timeToCollectDeletedDocs=19.50 ms, timeTakenToDeleteDocs=0.000 ns})
> .15:19:16.682 [DocumentNodeStore background update thread] INFO
> o.a.j.o.p.document.DocumentNodeStore - Background operations stats (clean:0,
> split:0, lock:35581, write:1, num:5)
> ............
> Performed RevisionGC in 8.449 s
> (VersionGCStats{ignoredGCDueToCheckPoint=false, deletedDocGCCount=2002,
> splitDocGCCount=0, intermediateSplitDocGCCount=0,
> timeToCollectDeletedDocs=8.276 s, timeTakenToDeleteDocs=171.7 ms})
> {noformat}
> The background update thread had to wait 35 seconds for the
> backgroundOperations lock, which was held by the committing thread:
> {noformat}
> "Thread-2" prio=5 tid=0x00007f986b9a7800 nid=0x6803 runnable
> [0x0000000112780000]
> java.lang.Thread.State: RUNNABLE
> at org.h2.compress.CompressLZF.compress(CompressLZF.java:239)
> at org.h2.mvstore.Page.write(Page.java:754)
> at org.h2.mvstore.Page.writeUnsavedRecursive(Page.java:816)
> at org.h2.mvstore.Page.writeUnsavedRecursive(Page.java:822)
> at org.h2.mvstore.Page.writeUnsavedRecursive(Page.java:822)
> at org.h2.mvstore.MVStore.storeNowTry(MVStore.java:1065)
> at org.h2.mvstore.MVStore.storeNow(MVStore.java:981)
> at org.h2.mvstore.MVStore.commitAndSave(MVStore.java:970)
> - locked <0x00000007e15cccf0> (a org.h2.mvstore.MVStore)
> at org.h2.mvstore.MVStore.beforeWrite(MVStore.java:2084)
> at org.h2.mvstore.MVMap.beforeWrite(MVMap.java:1046)
> at org.h2.mvstore.MVMap.copy(MVMap.java:1231)
> at org.h2.mvstore.MVMap.copy(MVMap.java:1248)
> at org.h2.mvstore.MVMap.copy(MVMap.java:1248)
> at org.h2.mvstore.MVMap.copyFrom(MVMap.java:1218)
> at org.h2.mvstore.MVStoreTool.compact(MVStoreTool.java:493)
> at org.h2.mvstore.MVStoreTool.compact(MVStoreTool.java:458)
> at org.h2.mvstore.MVStoreTool.compact(MVStoreTool.java:404)
> at
> org.apache.jackrabbit.oak.plugins.document.persistentCache.PersistentCache$1.closeStore(PersistentCache.java:235)
> - locked <0x00000007c0c82760> (a
> org.apache.jackrabbit.oak.plugins.document.persistentCache.PersistentCache$1)
> at
> org.apache.jackrabbit.oak.plugins.document.persistentCache.PersistentCache.switchGenerationIfNeeded(PersistentCache.java:372)
> - locked <0x00000007c03a6c00> (a
> org.apache.jackrabbit.oak.plugins.document.persistentCache.PersistentCache)
> at
> org.apache.jackrabbit.oak.plugins.document.persistentCache.NodeCache.write(NodeCache.java:85)
> at
> org.apache.jackrabbit.oak.plugins.document.persistentCache.NodeCache.put(NodeCache.java:130)
> at
> org.apache.jackrabbit.oak.plugins.document.LocalDiffCache$1.done(LocalDiffCache.java:98)
> at
> org.apache.jackrabbit.oak.plugins.document.Commit.applyToCache(Commit.java:602)
> at
> org.apache.jackrabbit.oak.plugins.document.CommitQueue.afterTrunkCommit(CommitQueue.java:127)
> - locked <0x00000007c03a46f0> (a
> org.apache.jackrabbit.oak.plugins.document.CommitQueue)
> at
> org.apache.jackrabbit.oak.plugins.document.CommitQueue.done(CommitQueue.java:83)
> at
> org.apache.jackrabbit.oak.plugins.document.DocumentNodeStore.done(DocumentNodeStore.java:644)
> at
> org.apache.jackrabbit.oak.plugins.document.DocumentNodeStoreBranch.persist(DocumentNodeStoreBranch.java:338)
> at
> org.apache.jackrabbit.oak.plugins.document.DocumentNodeStoreBranch.persist(DocumentNodeStoreBranch.java:304)
> at
> org.apache.jackrabbit.oak.plugins.document.DocumentNodeStoreBranch.access$200(DocumentNodeStoreBranch.java:52)
> at
> org.apache.jackrabbit.oak.plugins.document.DocumentNodeStoreBranch$InMemory.merge(DocumentNodeStoreBranch.java:541)
> at
> org.apache.jackrabbit.oak.plugins.document.DocumentNodeStoreBranch.merge0(DocumentNodeStoreBranch.java:230)
> at
> org.apache.jackrabbit.oak.plugins.document.DocumentNodeStoreBranch.merge(DocumentNodeStoreBranch.java:171)
> at
> org.apache.jackrabbit.oak.plugins.document.DocumentRootBuilder.merge(DocumentRootBuilder.java:158)
> at
> org.apache.jackrabbit.oak.plugins.document.DocumentNodeStore.merge(DocumentNodeStore.java:1490)
> at
> org.apache.jackrabbit.oak.core.MutableRoot.commit(MutableRoot.java:247)
> at
> org.apache.jackrabbit.oak.jcr.delegate.SessionDelegate.commit(SessionDelegate.java:341)
> at
> org.apache.jackrabbit.oak.jcr.delegate.SessionDelegate.save(SessionDelegate.java:487)
> at
> org.apache.jackrabbit.oak.jcr.session.SessionImpl$8.performVoid(SessionImpl.java:424)
> at
> org.apache.jackrabbit.oak.jcr.delegate.SessionDelegate.performVoid(SessionDelegate.java:268)
> at
> org.apache.jackrabbit.oak.jcr.session.SessionImpl.save(SessionImpl.java:421)
> at
> org.apache.jackrabbit.oak.ContinuousRevisionGCTest$Writer.run(ContinuousRevisionGCTest.java:72)
> at java.lang.Thread.run(Thread.java:745)
> {noformat}
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