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https://issues.apache.org/jira/browse/DERBY-2911?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Knut Anders Hatlen updated DERBY-2911:
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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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