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From Øystein Grøvlen (JIRA) <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-801) Allow parallel access to data files.
Date Wed, 18 Oct 2006 13:10:37 GMT
    [ http://issues.apache.org/jira/browse/DERBY-801?page=comments#action_12443260 ] 
            
Øystein Grøvlen commented on DERBY-801:
---------------------------------------

I saw the above error when developing the LobLengthTest, but it went away after I made some
changes to the test.  One of the changes I made was that the test was run earlier in the suite.
 Knut Anders' guess may explain this since my changes may have changed the possibility of
running the test concurrently with checkpointing.  The reason the problem hits this test may
be that the table has probably allocated more blocks that any of the other tests in the suite
(It inserts a16MB blob).  

> 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, 10.1.2.1
>         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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