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https://issues.apache.org/jira/browse/DERBY-3280?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Knut Anders Hatlen updated DERBY-3280:
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Derby Info: [Patch Available]
> Poor distribution of hash values from RecordId.hashCode()
> ---------------------------------------------------------
>
> Key: DERBY-3280
> URL: https://issues.apache.org/jira/browse/DERBY-3280
> Project: Derby
> Issue Type: Improvement
> Components: Performance, Services, Store
> Affects Versions: 10.4.0.0
> Reporter: Knut Anders Hatlen
> Assignee: Knut Anders Hatlen
> Attachments: d3280.diff, TestClient.java
>
>
> The hash values returned by RecordId.hashCode() are constructed by performing
> bitwise xor on the 32 least significant bits of the record number, the page
> number, the container id and the segment id. Since all of these values tend
> to be relatively small positive integers, the hash values also tend to be
> clustered in a very small range. This leads to a higher frequency of hash
> collisions in the lock table, which makes the hash tables work less
> efficiently and thereby reduces the performance.
> As an example, the simple join load in the test client attached to DERBY-1961
> uses two tables, TENKTUP and ONEKTUP, with 10000 rows and 1000 rows,
> respectively. The RecordIds for these 11000 rows map to less than 900
> distinct hash codes.
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