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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3885) Latch contention in B-tree on multi-core systems
Date Fri, 26 Sep 2008 13:59:44 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3885?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12634870#action_12634870
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Knut Anders Hatlen commented on DERBY-3885:
-------------------------------------------

The master thesis "Apache Derby SMP scalability" by Anders Morken and Per Ottar Ribe Pahr
describes some interesting ideas. It can be downloaded from http://daim.idi.ntnu.no/show.php?type=masteroppgave&id=3394.
The idea is basically to introduce the concept of shared latches, so that multiple readers
may access the nodes of the B-tree concurrently. This apparently had a positive effect on
the performance in a multi-threaded environment on multi-core systems.

> Latch contention in B-tree on multi-core systems
> ------------------------------------------------
>
>                 Key: DERBY-3885
>                 URL: https://issues.apache.org/jira/browse/DERBY-3885
>             Project: Derby
>          Issue Type: Improvement
>          Components: Performance, Store
>    Affects Versions: 10.4.2.0
>            Reporter: Knut Anders Hatlen
>            Priority: Minor
>
> When you have many concurrent threads accessing rows in the same table via an index,
the root of the B-tree becomes a hot spot. Since access to a node in the B-tree is single-threaded
(an exclusive latch is held while a binary search is performed on the node) this limits the
scalability on multi-core systems. We should try to find a way to allow multiple threads to
navigate the B-tree concurrently without blocking each other.

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