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https://issues.apache.org/jira/browse/JCR-2524?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12840074#action_12840074
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Thomas Mueller commented on JCR-2524:
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> Caching the most recently used DocIds and reuse them might help to reduce the
> memory usage
+1
> DocIds that could be represented with a short instead of an int
According to my test, this will not reduce memory usage:
http://h2database.com/p.html#da4c6a321d0dc84a2b7b96cdbf468a47
For the Sun JVM (JDK 1.5, 32 bit), objects with one field of type boolean,
byte, short, character, integer, and long all need 16 bytes. A small BigInteger
uses 56 bytes, a small BigDecimal uses 32 bytes (probably re-uses the same
BigInteger internally), and a String uses 24 bytes. Object uses 8 bytes.
For JDK 1.6, 32 bit and 64 bit, it's a bit different: 20 bytes for an object,
24 bytes for boolean - long.
For JDK 1.5, 64 bit, it's again different: 16 bytes for an object, 24 bytes for
boolean - long.
> Reduce memory usage of DocIds
> -----------------------------
>
> Key: JCR-2524
> URL: https://issues.apache.org/jira/browse/JCR-2524
> Project: Jackrabbit Content Repository
> Issue Type: Improvement
> Components: jackrabbit-core
> Reporter: Marcel Reutegger
> Priority: Minor
> Attachments: JCR-2524.patch
>
>
> Implementations of DocIds are used to cache parent child relations of nodes
> in the index. Usually there are a lot of duplicate objects because a DocId
> instance is used to identify the parent of a node in the index. That is,
> sibling nodes will all have DocIds with the same value. Currently a new DocId
> instance is created for each node. Caching the most recently used DocIds and
> reuse them might help to reduce the memory usage. Furthermore there are
> DocIds that could be represented with a short instead of an int when possible.
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