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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 Mon, 03 Sep 2007 14:08:58 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: d2911-1.stat

Attached is a partial implementation of a new buffer manager. It adds a class called ConcurrentCache,
which implements the CacheManager interface and keeps the cached objects in a ConcurrentHashMap.
It also adds ConcurrentCacheFactory, which creates instances of the new cache, and CacheEntry,
which represents an entry in the cache and uses a ReentrantLock to protect its internal state
from concurrent accesses.

Currently, only basic operations like find, release, release, remove and clean have been implemented.
There is no replacement algorithm, which basically means that the cache doesn't have a defined
maximum size. I managed to run the attached performance test with the patch (manually edited
modules.properties to load the new buffer manager). It showed promising results. With 100
threads on a machine with eight CPUs, the throughput was almost doubled. With fewer threads
(or fewer CPUs) there was of course less improvement. I didn't notice any performance loss
for the single-threaded case, though.

> 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:
>            Reporter: Knut Anders Hatlen
>            Assignee: Knut Anders Hatlen
>            Priority: Minor
>         Attachments: d2911-1.diff, d2911-1.stat, d2911-unused.diff, d2911-unused.stat,
> 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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