[DERBY-801] Allow parallel access to data files.

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 10.0.2.0, 10.0.2.1, 10.1.1.0, 10.1.2.1
• Fix Version/s: 10.3.1.4
• Component/s: Store
• Environment: Any
• Bug behavior facts: Performance
• Assignee: Anders Morken
• Reporter: Oystein Grovlen
• Created: 09/Jan/06 19:43
• Updated: 29/Jun/09 14:41
• Resolved: 15/Nov/06 15:55

Description

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

Issue Links

• is related to: DERBY-262 Use Java 1.5 NIO for improved performance