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From "Nicolas Labrot (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-1043) Faster UUID comparisons
Date Mon, 03 May 2010 21:04:59 GMT

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Nicolas Labrot commented on CASSANDRA-1043:
-------------------------------------------

I will just add a comment on the test. Like the optimisation uses the internal structure of
Jug UUID it should be valusable to add a test on it.

for example with asserts on value of UUID.INDEX_CLOCK_HI, UUID.INDEX_CLOCK_MID and INDEX_CLOCK_MID.INDEX_CLOCK_LO

> Faster UUID comparisons
> -----------------------
>
>                 Key: CASSANDRA-1043
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1043
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: James Golick
>            Assignee: James Golick
>            Priority: Minor
>             Fix For: 0.7
>
>         Attachments: faster-uuid-compare-v3.diff, faster_uuid_compare.diff, patch-v2-with-tests.diff
>
>
> As I explained on the mailing list, doing slice queries on CFs that are sorted by TimeUUIDType
gets slower as the value of count increases. According to my profiles, this is largely due
to the fact that ConcurrentSkipListMap calls the comparator very frequently, which is extremely
inefficient. In order to compare two UUIDs, it has to materialize them both in to java.util.UUID
objects which is quite slow. The more UUIDs to compare, the slower it is.
> Attached is a patch that compares UUIDs by extracting the timestamp directly from the
byte[] representation. According to my tests, it's close to a 50% performance improvement.

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