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From Tomek Rękawek (JIRA) <j...@apache.org>
Subject [jira] [Commented] (OAK-4882) Bottleneck in the asynchronous persistent cache
Date Fri, 21 Oct 2016 10:57:58 GMT

    [ https://issues.apache.org/jira/browse/OAK-4882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15594791#comment-15594791
] 

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

The first possible improvement is to remove the {{synchronized}} keyword from the {{CacheActionDispatcher}}:

{noformat}
--- a/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/persistentCache/async/CacheActionDispatcher.java
+++ b/oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/persistentCache/async/CacheActionDispatcher.java
@@ -83,7 +83,7 @@ public class CacheActionDispatcher implements Runnable {
      *
      * @param action to be added
      */
-    synchronized void add(CacheAction<?, ?> action) {
+    void add(CacheAction<?, ?> action) {
         if (queue.size() >= MAX_SIZE) {
             cleanTheQueue();
         }
{noformat}

The {{queue}} is synchronized anyway and the cleanTheQueue() operation doesn't have to be
executed atomically.

> 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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