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  1. Wicket
  2. WICKET-5527

Inefficient DefaultPageStore.SerializedPagesCache


    • Type: Bug
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: 6.14.0
    • Fix Version/s: 7.0.0-M1
    • Component/s: wicket
    • Labels:


      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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              • Assignee:
                mgrigorov Martin Grigorov
                mgrigorov Martin Grigorov
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