Reducing Threads in the TimeAndSizeRollingAppender

Several people have commented that the TimeAndSizeRollingAppender could, where many instances were configured, launch many threads.  With date roll enforcement, backup log file scavenging, and backup log file compression all configured, there could be 3 threads per TASRA instance.  That simply didn’t scale.  The original design assumption that only one or two TASRA instances would be configured per application was clearly broken.

I have begun some work to minimise the number of threads launched where multiple TASRA instances are configured.  The first fruits of that have been released and can be downloaded from www.simonsite.org.uk.

The changes permit an arbitrary number of TASRA instances to share a single thread for all backup log file scavenging and backup log file compression tasks.  Date roll enforcement is still carried out on a separate daemon thread, for now.

The benefit is best illustrated with some numbers; taking an arbitrary 10 TASRA instances as opposed to just one to better illustrate the effect:

TASRA configuration	Daemon thread count per 10 TASRA instances
	20120703-0826 Release	20130130-1840 Release
ScavengeInterval=300000, DateRollEnforced=true, CompressionAlgorithm=ZIP	30	11
ScavengeInterval=300000, DateRollEnforced=false, CompressionAlgorithm=ZIP	20	1
ScavengeInterval=300000, DateRollEnforced=false, CompressionAlgorithm=default (not set)	10	1
ScavengeInterval=-1, DateRollEnforced=false, CompressionAlgorithm=default	0	0

By default, all TASRA instances will now share the same thread.  Optionally, m TASRA instances may be configured to use n threads, where m >= n >= 1.  To do this, a common named object must be shared by all TASRA instances that will share the same thread, and distinct named object(s) for any other TASRA instances that will use different thread(s).  The following sample configuration illustrates two TASRA instances, “appender-1” and “appender-2”, each using its own thread, “executor-1” or “executor-2”, respectively, in this case for scavenging and compression tasks:

       <appender name="file-appender-1"

              class="uk.org.simonsite.log4j.appender.TimeAndSizeRollingAppender">

              <param name="File" value="${tasra.xml.test.log.file.1}" />

              <layout class="org.apache.log4j.SimpleLayout" />

              <param name="CompressionAlgorithm" value="ZIP" />

              <logTaskExecutorService class="uk.org.simonsite.log4j.appender.NamedLoggingTaskExecutorService">

                     <param name="Name" value="executor-1" />

              </logTaskExecutorService>

       </appender>

       <appender name="file-appender-2"

              class="uk.org.simonsite.log4j.appender.TimeAndSizeRollingAppender">

              <param name="File" value="${tasra.xml.test.log.file.2}" />

              <layout class="org.apache.log4j.SimpleLayout" />

<param name="CompressionAlgorithm" value="ZIP" />

              <logTaskExecutorService class="uk.org.simonsite.log4j.appender.NamedLoggingTaskExecutorService">

                     <param name="Name" value="executor-2" />

              </logTaskExecutorService>

       </appender>