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From Tomek Rękawek (JIRA) <j...@apache.org>
Subject [jira] [Commented] (OAK-4882) Bottleneck in the asynchronous persistent cache
Date Tue, 25 Oct 2016 11:43:58 GMT

    [ https://issues.apache.org/jira/browse/OAK-4882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15605044#comment-15605044
] 

Tomek Rękawek commented on OAK-4882:
------------------------------------

[~tmueller], [~mmarth], great, thanks for the feedback.

So, I was thinking about naive approach in which we just drop the new put/invalidate actions
if the queue if already full. It's a bit aggressive, but will certainly fix all the bottlenecks
(as we won't wait for anything). Also, seems like a good starting point for the future improvements.
From what [~tmueller] wrote it seems it should behave correctly.

> Bottleneck in the asynchronous persistent cache
> -----------------------------------------------
>
>                 Key: OAK-4882
>                 URL: https://issues.apache.org/jira/browse/OAK-4882
>             Project: Jackrabbit Oak
>          Issue Type: Bug
>          Components: cache, documentmk
>    Affects Versions: 1.5.10, 1.4.8
>            Reporter: Tomek Rękawek
>            Assignee: Tomek Rękawek
>             Fix For: 1.6
>
>
> The class responsible for accepting new cache operations which will be handled asynchronously
is [CacheActionDispatcher|https://github.com/apache/jackrabbit-oak/blob/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/persistentCache/async/CacheActionDispatcher.java].
In case of a high load, when the queue is full (=1024 entries), the [add()|https://github.com/apache/jackrabbit-oak/blob/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/persistentCache/async/CacheActionDispatcher.java#L86]
method removes the oldest 256 entries. However, we can't afford losing the updates (as it
may result in having stale entries in the cache), so all the removed entries are compacted
into one big invalidate action.
> The compaction action ([CacheActionDispatcher#cleanTheQueue|https://github.com/apache/jackrabbit-oak/blob/trunk/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/persistentCache/async/CacheActionDispatcher.java#L97])
still holds the lock taken in add() method, so threads which tries to add something to the
queue have to wait until cleanTheQueue() ends.
> Maybe we can optimise the CacheActionDispatcher#add->cleanTheQueue part, so it won't
hold the lock for the whole time.



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