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Date: Fri, 14 Sep 2007 03:13:32 -0700 (PDT)
From: "Knut Anders Hatlen (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Updated: (DERBY-2911) Implement a buffer manager using
 java.util.concurrent classes
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     [ 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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