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From "Anders Morken (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-801) Allow parallel access to data files.
Date Thu, 02 Nov 2006 22:22:19 GMT
     [ http://issues.apache.org/jira/browse/DERBY-801?page=all ]

Anders Morken updated DERBY-801:
--------------------------------

    Attachment: DERBY-801-6.patch

DERBY-801-6.patch remedies the noise from the iosInProgress sanity checking by checking the
committed drop state before croaking. I've run jdbcapi/LobLengthTest.junit 100 times in a
row now without seeing any problems, and I used to see the problem once every four or five
runs without this patch.

 RAFContainer4.java |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletion(-)

I'm not sure checking for the committed drop state in the readPage method is something we
want to do - flushing the cache into a black hole is one thing, trying to read data that is
supposed to be gone is another - I think I'd want to know if we had some logic that permitted
reading from a dropped container. =)

I've sort of got a feeling that maybe we are masking a problem here - should anyone (even
the cache?) write to a dropped container? Maybe we should remove pages destined for a dying
container from the cache when the container is dropped? =)

> 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-801-6.patch, DERBY-801-v2.patch, DERBY-801-v3.patch, DERBY-801-v4.patch,
DERBY-801-v5.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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