Details
Major 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