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From Tomek Rękawek (JIRA) <j...@apache.org>
Subject [jira] [Commented] (OAK-2761) Persistent cache: add data in a different thread
Date Wed, 10 Feb 2016 08:10:18 GMT

    [ https://issues.apache.org/jira/browse/OAK-2761?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15140483#comment-15140483
] 

Tomek Rękawek commented on OAK-2761:
------------------------------------

bq. It would be good if the broadcasting cache would receive entries when they are added to
the (in-memory LIRS) cache, and the persistent storage of the cache (MVStore currently) would
get the entries when they are evicted.

This is exactly how it happens :)

bq. Another possible improvement is to only put those entries in the persistent storage if
they were accessed more than once. But this policy would need to be configurable so we can
test whether it helps (improve speed and reduce storage size).

Can we extract this as a separate issue? The patches are already pretty big.

> Persistent cache: add data in a different thread
> ------------------------------------------------
>
>                 Key: OAK-2761
>                 URL: https://issues.apache.org/jira/browse/OAK-2761
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: cache, core, mongomk
>            Reporter: Thomas Mueller
>            Assignee: Thomas Mueller
>              Labels: resilience
>             Fix For: 1.4
>
>         Attachments: AsyncCacheTest.patch, OAK-2761-1.2.patch, OAK-2761-trunk.patch
>
>
> The persistent cache usually stores data in a background thread, but sometimes (if a
lot of data is added quickly) the foreground thread is blocked.
> Even worse, switching the cache file can happen in a foreground thread, with the following
stack trace.
> {noformat}
> "127.0.0.1 [1428931262206] POST /bin/replicate.json HTTP/1.1" prio=5 tid=0x00007fe5df819800
nid=0x9907 runnable [0x0000000113fc4000]
>    java.lang.Thread.State: RUNNABLE
>         ...
> 	at org.h2.mvstore.MVStoreTool.compact(MVStoreTool.java:404)
> 	at org.apache.jackrabbit.oak.plugins.document.persistentCache.PersistentCache$1.closeStore(PersistentCache.java:213)
> 	- locked <0x0000000782483050> (a org.apache.jackrabbit.oak.plugins.document.persistentCache.PersistentCache$1)
> 	at org.apache.jackrabbit.oak.plugins.document.persistentCache.PersistentCache.switchGenerationIfNeeded(PersistentCache.java:350)
> 	- locked <0x0000000782455710> (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.DocumentNodeStore.applyChanges(DocumentNodeStore.java:1060)
> 	at org.apache.jackrabbit.oak.plugins.document.Commit.applyToCache(Commit.java:599)
> 	at org.apache.jackrabbit.oak.plugins.document.CommitQueue.afterTrunkCommit(CommitQueue.java:127)
> 	- locked <0x0000000781890788> (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:637)
> {noformat}
> To avoid blocking the foreground thread, one solution is to store all data in a separate
thread. If there is too much data added, then some of the data is not stored. If possible,
the data that was not referenced a lot, and / or old revisions of documents (if new revisions
are available).



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