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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 Fri, 14 Sep 2007 10:13:32 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-entry-javadoc.diff

Patch d2911-entry-javadoc.diff extends the class javadoc for CacheEntry with descriptions
of its different states. I also changed a note in the javadoc which said that one thread could
only hold the lock on one CacheEntry at a time to prevent deadlocks. Since the replacement
algorithm probably needs to hold the lock on two entries at a time (the entry that is about
to be inserted and the entry that is to be evicted), I loosened the single-lock-per-thread
requirement. Now the javadoc says that it is OK to hold the lock on two different CacheEntry
objects, as long as the first entry to be locked is in the uninitialized state and the second
entry is not in the uninitialized state. By enforcing a strict order for obtaining the locks,
concurrent threads won't run into deadlocks with each other.

> 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-entry-javadoc.diff,
d2911-unused.diff, d2911-unused.stat, d2911perf.java
>
>
> 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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