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https://issues.apache.org/jira/browse/WICKET-5527?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Martin Grigorov resolved WICKET-5527.
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Resolution: Fixed
Fix Version/s: 7.0.0
> Inefficient DefaultPageStore.SerializedPagesCache
> -------------------------------------------------
>
> Key: WICKET-5527
> URL: https://issues.apache.org/jira/browse/WICKET-5527
> Project: Wicket
> Issue Type: Bug
> Components: wicket
> Affects Versions: 6.14.0
> Reporter: Martin Grigorov
> Assignee: Martin Grigorov
> Fix For: 7.0.0
>
>
> We have identified some problems in
> org.apache.wicket.pageStore.DefaultPageStore.SerializedPagesCache.
> Some history first:
> At https://cwiki.apache.org/confluence/display/WICKET/Page+Storage I have
> explained how the page storage management works in Wicket 1.5+
> In brief:
> First level cache/store is the HttpSession - here Wicket saves the live
> instances of all touched pages in the last request cycle.
> Second level cache/store is DefaultPageStore.SerializedPagesCache - here
> Wicket saves the last N
> (org.apache.wicket.settings.StoreSettings#getInmemoryCacheSize) used pages in
> the whole application (by default 40 pages)
> Third level cache/store is DiskDataStore - here Wicket stores all pages and
> depending on org.apache.wicket.settings.StoreSettings#getMaxSizePerSession it
> will "recycle" the file contents
> The identified problems:
> - org.apache.wicket.pageStore.DefaultPageStore.SerializedPagesCache uses
> ArrayList as a data structure to keep SerializedPage instances. When the
> limit N (StoreSettings#getInmemoryCacheSize) is reached the ArrayList uses
> #remove() to remove the oldest entry. The #remove(0) operation internally
> uses System.arraycopy() to compact the internal array structure. As you
> already realize this ArrayList is constantly being recompacted in any
> application in production.
> - DefaultPageStore.SerializedPagesCache#cache (the same ArrayList) is used
> as synchronization monitor for every operation (read/write/remove). I.e. we
> have synchronization on application level !!
> - at the moment DefaultPageStore.SerializedPagesCache stores
> org.apache.wicket.pageStore.DefaultPageStore.SerializedPage. This is a
> structure of {String sessionId, int pageId, byte[] data}.
> Since this data is stored in the application scope it is never replicated, so
> there is no need to serialize the live page instance to byte[] at all. Only
> the third level cache (IDataStore) should work with byte[]
> A workaround to avoid the slowness caused by this is to set 0 or negative
> value to org.apache.wicket.settings.StoreSettings#setInmemoryCacheSize
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