Author: jdcryans
Date: Fri Dec 3 05:34:32 2010
New Revision: 1041696
URL: http://svn.apache.org/viewvc?rev=1041696&view=rev
Log:
doc for HBASE-3303
Modified:
hbase/trunk/src/docbkx/book.xml
Modified: hbase/trunk/src/docbkx/book.xml
URL:
http://svn.apache.org/viewvc/hbase/trunk/src/docbkx/book.xml?rev=1041696&r1=1041695&r2=1041696&view=diff
==============================================================================
--- hbase/trunk/src/docbkx/book.xml (original)
+++ hbase/trunk/src/docbkx/book.xml Fri Dec 3 05:34:32 2010
@@ -1009,6 +1009,33 @@ to ensure well-formedness of your docume
with configuration such as this.
</para>
</section>
+ <section
xml:id="hbase.regionserver.handler.count"><title><varname>hbase.regionserver.handler.count</varname></title>
+ <para>
+ This setting defines the number of threads that are kept open to
answer
+ incoming requests to user tables. The default of 10 is rather low in
order to
+ prevent users from killing their region servers when using large
write buffers
+ with a high number of concurrent clients. The rule of thumb is to
keep this
+ number low when the payload per request approaches the MB (big puts,
scans using
+ a large cache) and high when the payload is small (gets, small puts,
ICVs, deletes).
+ </para>
+ <para>
+ It is safe to set that number to the
+ maximum number of incoming clients if their payload is small, the
typical example
+ being a cluster that serves a website since puts aren't typically
buffered
+ and most of the operations are gets.
+ </para>
+ <para>
+ The reason why it is dangerous to keep this setting high is that the
aggregate
+ size of all the puts that are currently happening in a region server
may impose
+ too much pressure on its memory, or even trigger an
OutOfMemoryError. A region server
+ running on low memory will trigger its JVM's garbage collector to
run more frequently
+ up to a point where GC pauses become noticeable (the reason being
that all the memory
+ used to keep all the requests' payloads cannot be trashed, no matter
how hard the
+ garbage collector tries). After some time, the overall cluster
+ throughput is affected since every request that hits that region
server will take longer,
+ which exacerbates the problem even more.
+ </para>
+ </section>
<section xml:id="big_memory">
<title>Configuration for large memory machines</title>
<para>
