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From "Anders Morken (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-801) Allow parallel access to data files.
Date Thu, 02 Nov 2006 07:42:18 GMT
    [ http://issues.apache.org/jira/browse/DERBY-801?page=comments#action_12446493 ] 
            
Anders Morken commented on DERBY-801:
-------------------------------------

> Maybe moving the committedDropState check to the start of writePage and skipping the
write altogether if it is in that state is a good approach?

Never mind my ramblings, we already do that. OK, maybe we could check the committedDropState
in the (iosInProgress == 0) assertion in closePage as well? All of this mess (iosInProgress
and the associated assertions) is intended as a sanity checking aid, and if we agree that
closing a container that is being dropped while IO is still active on it is sane, it shouldn't
be a source of noise.

> 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, 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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