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https://issues.apache.org/jira/browse/COCOON-2146?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12545589
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ellispritchard edited comment on COCOON-2146 at 11/26/07 12:27 PM:
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Thanks for your comment, Ard.
Your analysis may well explain some performance problems we were seeing on our
system; unfortunately I was not around at the time to analyze them, so I can't
really be sure what caused them. The action they took at the time was simply to
cache less, i.e. only the expensive stuff, rather than, well, basically
everything!
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?
I think that ehcache 1.4 (now in beta) may provide at least one solution to
this problem, with its new listeners functionality, which can get notification
of the keys of entries removed (for any reason) from the cache.
However, maybe there's a 'redesign the whole thing' kind of solution too?
As for whether we need it or not: according to "the powers that be" we do need
a persistent cache, so that when we bring the site up under load, on n
instances (each with their own cache), it doesn't hammer our database. The fact
that the site was running without one for 8 months due to this bug is not
enough to convince them otherwise! It's either that, or having to pre-warm the
cache during site-down time (and making site down time longer), or even worse,
running the whole site behind mod_cache with an expiry time of about an hour or
so, to cover any lag in getting it up again. A persistent EventCache just looks
so attractive compared to those options...
was (Author: ellispritchard):
Thanks for your comment, Ard.
Your analysis may well explain some performance problems we were seeing on our
system; unfortunately I was not around at the time to analyze them, so I can't
really be sure what caused them. The action they took at the time was simply to
cache less, i.e. only the expensive stuff, rather than, well, basically
everything!
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?
I think that ehcache 1.4 (now in beta) may provide at least one solution to
this problem, with its new listeners functionality, which can get notification
of the keys of entries removed (for any reason) from the cache.
However, maybe there's a 'redesign the whole thing' kind of solution too?
As for whether we need it or not: according to "the powers that be" we do need
a persistent cache, so that when we bring the site up under load, on n
instances (each with their own cache), it doesn't hammer our database. The fact
that was running without one for 8 months due to this bug is not enough to
convince them otherwise! It's either that, or having to pre-warm the cache
during site-down time (and making site down time longer), or even worse,
running the whole site behind mod_cache with an expiry time of about an hour or
so, to cover any lag in getting it up again. A persistent EventCache just looks
so attractive compared to those options...
> 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, 2.1.11-dev (Current SVN)
> Reporter: Ellis Pritchard
> Assignee: Grzegorz Kossakowski
> 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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