[jira] Commented: (DERBY-2911) Implement a buffer manager using java.util.concurrent classes

["Knut Anders Hatlen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-2911?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12531521 ] 

Knut Anders Hatlen commented on DERBY-2911:
-------------------------------------------

I don't understand why unit/T_RawStoreFactory.unit fails. Or to be more specific, I don't understand the connection between the failure and the buffer manager. The failure is caused by some pages not being freed (that is, marked as free in the alloc page) on a rollback to savepoint in T_RawStoreFactory.P042(). What's strange is that

  - with Clock (old buffer manager) it works fine

  - when the scan for invalid items to reuse in Clock.findFreeItem() is commented out, it fails

  - with unmodified Clock, and all test cases except P042() commented out, it fails

So it seems like the result of P042 is somehow dependent on the contents of the page cache (or perhaps the container cache?) when the test case starts, which is strange both because I thought the alloc page didn't care whether a page was in the cache or not, and because the test case creates a new container at the beginning so that none of the pages used in the test should be present in the cache anyway.

> 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: d2911-1.diff, d2911-1.stat, d2911-2.diff, d2911-3.diff, d2911-4.diff, d2911-5.diff, d2911-6.diff, d2911-6.stat, d2911-entry-javadoc.diff, d2911-unused.diff, d2911-unused.stat, d2911perf.java, perftest6.pdf
>
>
> 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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