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From "Anders Morken (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-801) Allow parallel access to data files.
Date Tue, 19 Sep 2006 06:10:28 GMT
    [ http://issues.apache.org/jira/browse/DERBY-801?page=comments#action_12435677 ] 
            
Anders Morken commented on DERBY-801:
-------------------------------------

Suresh, Knut Anders, thanks for your advice. There's no need to rush this patch for my part,
I'll be happy to provide a new one incorporating Suresh' suggestions. They probably end up
making the whole patch smaller, as most of it is about removing redundant code (such as my
homegrown RAFContainerFactory). I've already fixed 2) and 3) in my working copy, and I plan
to take a long, hard look at 1) tonight. =)

> Allow parallel access to data files.
> ------------------------------------
>
>                 Key: DERBY-801
>                 URL: http://issues.apache.org/jira/browse/DERBY-801
>             Project: Derby
>          Issue Type: Improvement
>          Components: Performance, Store
>    Affects Versions: 10.0.2.0, 10.0.2.1, 10.1.1.0, 10.1.1.1, 10.1.1.2, 10.1.2.0, 10.1.2.1
>         Environment: Any
>            Reporter: Øystein Grøvlen
>         Assigned To: Anders Morken
>         Attachments: DERBY-801-v2.patch, DERBY-801-v3.patch, DERBY-801-v4.patch, NIO-RAFContainer-v1.patch
>
>
> Derby currently serializes accesses to a data file.  For example, the
> implementation of RAFContainer.readPage is as follows:
>     synchronized (this) {  // 'this' is a FileContainer, i.e. a file object
>         fileData.seek(pageOffset);  // fileData is a RandomAccessFile
>         fileData.readFully(pageData, 0, pageSize);
>     }
> I have experiemented with a patch where I have introduced several file
> descriptors (RandomAccessFile objects) per RAFContainer.  These are
> used for reading.  The principle is that when all readers are busy, a
> readPage request will create a new reader.  (There is a maximum number
> of readers.)  With this patch, throughput was improved by 50% on
> linux.  For more discussion on this, see
> http://www.nabble.com/Derby-I-O-issues-during-checkpointing-t473523.html
> The challenge with the suggested approach is to make a mechanism to
> limit the number of open file descpriptors.  Mike Matrigali has
> suggested to use the existing CacheManager infrastructure for this
> purpose.  For a discussion on that, see:
> http://www.nabble.com/new-uses-for-basic-services-cache---looking-for-advice-t756863.html

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