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https://issues.apache.org/jira/browse/COCOON-2146?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12545761
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Ard Schrijvers commented on COCOON-2146:
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"Presumably though, if site-usage is fairly uniform, stuff that expires and is
still referenced from AbstractDoubleMapEventRegistry will get regenerated again
at some fairly near point, and replace the old entry with the new one, allowing
it to be freed by the JVM? Only if you're generating lots of unique pages or
short-lived pages and caching them for a long time may it become a 'real'
problem? "
Yes, you would think you absolutely had a point here.....but, unfortunately I
found out, that the MultiHashMap doen *not* act that way !! (note, it has been
a year, and i am not in a position now to dive in the code again but from the
top of my head) :
If you have a MultiHashMap and you put something like
m_keyMMap.put("key1", "value1"); multiple times, your map grows! you'll have 5
times "value1" in it (obviously from a performance POV this is easy to
understand)
So, exactly what you describe above, will result in OOM. Even if you have only
a few possible links, resulting in limited cachekeys, you'll run into OOM in
the end....I am sorry :-)
Anyway, the WeakReference solution is capable of being persisted, but needs
some extra stuff to be done at restart. OTOH, notification from ehcache with
some listeners might be a solution as well, though
1) it has to be independant of ehcache
2) I still think a DoubleMap is really not the way it should be solved. I would
always use WeakReferences for these kind of problems, because the overhead of
keeping the maps in sync is not needed.
> Using EventAware cache implementation breaks persistent cache restore on
> restart
> --------------------------------------------------------------------------------
>
> Key: COCOON-2146
> URL: https://issues.apache.org/jira/browse/COCOON-2146
> Project: Cocoon
> Issue Type: Bug
> Components: Blocks: Event Cache
> Affects Versions: 2.1.10
> Reporter: Ellis Pritchard
> Assignee: Jörg Heinicke
> Priority: Minor
> Fix For: 2.1.11-dev (Current SVN)
>
> Attachments: patch.txt
>
>
> In revision 412307 (Cocoon 2.1.10), AbstractDoubleMapEventRegistry and
> EventRegistryDataWrapper were changed (without an informative SVN comment!)
> to use the commons MultiValueMap instead of the MultiHashMap; I presume this
> was done in good faith because the latter map is deprecated and will be
> removed from Apache commons-collections 4.0
> However, as a result, the persistent cache cannot be restored if the
> EventAware cache implementation is used, since MultiValueMap is not
> Serializable! The old MultiHashMap was...
> Depending on whether StoreEventRegistryImpl or DefaultEventRegistryImpl is
> used, either the event cache index is never written (ehcache doesn't store
> non-serializable objects on disk), or a java.io.NotSerializableException is
> thrown (and caught, causing a full cache-clear) when attempting to restore
> the event cache index.
> This is Major for us, since we use Event-based caching alot, and this is
> causing the *entire* cache to no-longer persist across restarts (it's been
> like that for 8 months, since I upgraded Cocoon to 2.1.10 in the last week I
> was working here, and now I'm back, they've actually noticed!!)
> Work-around at the moment is to down-grade AbstractDoubleMapEventRegistry and
> EventRegistryDataWrapper to the 2.1.9 versions (pre-412307), which works so
> long as Apache-commons 3.x is still in use.
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