[jira] [Issue Comment Deleted] (OAK-2761) Persistent cache: add data in a different thread

["Tomek Rękawek (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/OAK-2761?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Tomek Rękawek updated OAK-2761:
-------------------------------
    Comment: was deleted

(was: The linked patch contains a draft of the solution:

https://github.com/trekawek/jackrabbit-oak/pull/5
https://github.com/trekawek/jackrabbit-oak/pull/5.diff

It uses two queues (as we have two maps in the {{NodeDocumentCache}}). The queue contains atomic cache operation, like {{put}}, {{putIfAbsent}}, {{putIfNewer}}, {{replace}}, {{invalidate}} or {{invalidateAll}}.

In order to avoid situation in which someone puts a document into cache and then gets the older version (because the put operation is still in the queue), the {{get()}} method returns {{null}} for all keys waiting to be processed.

If the queue is full, it'll be cleared. All documents which should have been affected by the queue operations are invalidated to avoid outdated read as above.

The most difficult part was the {{get(CacheValue, Callable)}} - it's get+put and can't be simply transformed into an asynchronous operation. I'm trying to find an workaround for this. Probably this is the cause of the failing unit tests.)

> 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: Bug
>          Components: cache, core, mongomk
>            Reporter: Thomas Mueller
>            Assignee: Thomas Mueller
>              Labels: resilience
>             Fix For: 1.4, 1.3.15
>
>
> 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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