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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-2911) Implement a buffer manager using java.util.concurrent classes
Date Wed, 12 Mar 2008 14:42:48 GMT

     [ https://issues.apache.org/jira/browse/DERBY-2911?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Knut Anders Hatlen updated DERBY-2911:
--------------------------------------

    Attachment: d2911-13.diff

Attaching a patch (d2911-13) which addresses 2a and 4h. I have started the regression tests
suite.

2a: Instead of inventing a new name for lockWhenIdentityIsSet(), I created a new method waitUntilIdentityIsSet()
and let the callers first invoke lock() and then waitUntilIdentityIsSet(). I think that makes
the code clearer.

4h: I created named constants for the numeric constants in rotateClock() and shrinkMe(). I
didn't make any changes to trimMe(), since I'm wondering if it's best just to remove it.

After this patch, I think it's only 4g (explain the heuristics in ClockPolicy.trimMe()) that
hasn't been addressed. I believe that trimMe() in reality is dead code (supported by the fact
that its predecessor Clock.trimToSize() is always a no-op in the regression tests according
to the test coverage reports), and a better and more reliable solution for the problem it
tries to solve, is to reduce the cache size. Unless someone comes up with a situation where
Clock.trimToSize() and ClockPolicy.trimMe() provide valuable functionality, I'm inclined to
remove the latter.

> Implement a buffer manager using java.util.concurrent classes
> -------------------------------------------------------------
>
>                 Key: DERBY-2911
>                 URL: https://issues.apache.org/jira/browse/DERBY-2911
>             Project: Derby
>          Issue Type: Improvement
>          Components: Performance, Services
>    Affects Versions: 10.4.0.0
>            Reporter: Knut Anders Hatlen
>            Assignee: Knut Anders Hatlen
>            Priority: Minor
>         Attachments: cleaner.diff, cleaner.tar, d2911-1.diff, d2911-1.stat, d2911-10.diff,
d2911-10.stat, d2911-11.diff, d2911-12.diff, d2911-13.diff, d2911-2.diff, d2911-3.diff, d2911-4.diff,
d2911-5.diff, d2911-6.diff, d2911-6.stat, d2911-7.diff, d2911-7a.diff, d2911-9.diff, d2911-9.stat,
d2911-enable.diff, d2911-entry-javadoc.diff, d2911-unused.diff, d2911-unused.stat, d2911perf.java,
derby-2911-8.diff, derby-2911-8.stat, perftest.diff, perftest.pdf, perftest.stat, perftest2.diff,
perftest6.pdf, poisson_patch8.tar
>
>
> There are indications that the buffer manager is a bottleneck for some types of multi-user
load. For instance, Anders Morken wrote this in a comment on DERBY-1704: "With a separate
table and index for each thread (to remove latch contention and lock waits from the equation)
we (...) found that org.apache.derby.impl.services.cache.Clock.find()/release() caused about
5 times more contention than the synchronization in LockSet.lockObject() and LockSet.unlock().
That might be an indicator of where to apply the next push".
> It would be interesting to see the scalability and performance of a buffer manager which
exploits the concurrency utilities added in Java SE 5.

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