[jira] Updated: (DERBY-801) Allow parallel access to data files.

["Anders Morken (JIRA)" <de...@db.apache.org>]

     [ http://issues.apache.org/jira/browse/DERBY-801?page=all ]

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

    Attachment: DERBY-801-v3.patch

DERBY-801-v3.patch is a cleaned up version of DERBY-801-v2.patch.

First off, thanks to Knut Anders for a thorough review - I appreciate it, even the 
nitpicking. Part of my motivation for doing this is to get rid of my bad habits. =)

Now, about this patch - I'll just reply to KAH's comments in the order they appeared.

1) I didn't particularly feel like modifying the interfaces in this patch. 
   Incremental development, right? ;-) Maybe we should stick a note in JIRA about it.

   The problem with the instanceof check is that RAFContainer4 will fall back to old
   behavior on tests that utilize the functionTests/util/corruptio/CorruptRandomAccessFile
   class to simulate a broken file, and thus it won't be tested there. May not really be an
   issue now, but could be one in a similar case later. Maybe I'm just paranoid. =)

2) OK =)

3) Good point, fixed.

4) updatePageArray() was only called from within a synchronized block before, so I
   didn't trust it to be MT-safe. To make the fast path lock-free I moved the synchronization
   inside the if/else blocks. Could be removed if you're sure it's safe? =)

5-14) Thanks, fixed. =)

I've tried to make sure the code adheres to the Java Coding Conventions now. I made one
exception (hopefully for the better): after a method head/if condition has been broken into multiple
lines I've used a newline before the { to make it easier to spot where the method head ends and 
the body starts. Should be quick to fix if you disagree with me, anyway. =)

> 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, 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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