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Added more detail on multi-threaded step

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dsyer
2010-08-26 06:10:47 +00:00
parent b37dbd2c06
commit 5f48fccd2f
1 changed files with 23 additions and 5 deletions
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28
src/site/docbook/reference/scalability.xml
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@@ -60,11 +60,14 @@
<para>The result of the above configuration will be that the Step
executes by reading, processing and writing each chunk of items
(each commit interval) in a separate thread of execution. In
addition to any limits placed by the task executor (e.g. if it is
backed by a thread pool), there is a throttle limit in the tasklet
which defaults to 6. You may need to increase this to ensure that
a thread pool is fully utililsed, e.g.</para>
(each commit interval) in a separate thread of execution. Note
that this means there is no fixed order for the items to be
processed, and a chunk might contain items that are
non-consecutive compared to the single-threaded case. In addition
to any limits placed by the task executor (e.g. if it is backed by
a thread pool), there is a throttle limit in the tasklet
configuration which defaults to 6. You may need to increase this
to ensure that a thread pool is fully utilised, e.g.</para>
<programlisting>&lt;step id="loading"&gt; &lt;tasklet
task-executor="taskExecutor"
@@ -87,6 +90,21 @@
(parallelJob) in the Spring Batch Samples that show the use of a process
indicator (see <xref linkend="process-indicator" xreflabel="" />) to keep
track of items that have been processed in a database input table.</para>
<para>Spring Batch provides some implementations of
<classname>ItemWriter</classname> and
<classname>ItemReader</classname>. Usually they say in the
Javadocs if they are thread safe or not, or what you have to do to
avoid problems in a concurrent environment. If there is no
information in Javadocs, you can check the implementation to see
if there is any state. If a reader is not thread safe, it may
still be efficient to use it in your own synchronizing delegator.
You can synchronize the call to <literal>read()</literal> and as
long as the processing and writing is the most expensive part of
the chunk your step may still complete much faster than in a
single threaded configuration.
</para>
</section>
<section id="scalabilityParallelSteps">