From fe60d5dce8f175ea72c879d790e224bd6c734e0d Mon Sep 17 00:00:00 2001
From: Michael Stack <stack@apache.org>
Date: Mon, 12 Dec 2011 18:34:17 +0000
Subject: [PATCH] HBASE-5000 Speed up simultaneous reads of a block when block
 caching is turned off; bit of doc and why its a bad idea disabling block
 cache completely

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1213354 13f79535-47bb-0310-9956-ffa450edef68
---
 src/docbkx/configuration.xml | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/docbkx/configuration.xml b/src/docbkx/configuration.xml
index 4b9cdb5edf4..7fd90e73ad4 100644
--- a/src/docbkx/configuration.xml
+++ b/src/docbkx/configuration.xml
@@ -1551,6 +1551,14 @@ of all regions.
            <para>See <xref linkend="master.processes.loadbalancer" /> for more information on the LoadBalancer.
            </para>
          </section>
+         <section xml:id="disabling.blockcache"><title>Disabling Blockcache</title>
+           <para>Do not turn off block cache (You'd do it by setting <varname>hbase.block.cache.size</varname> to zero).
+           Currently we do not do well if you do this because the regionserver will spend all its time loading hfile
+           indices over and over again.  If your working set it such that block cache does you no good, at least
+           size the block cache such that hfile indices will stay up in the cache (you can get a rough idea
+           on the size you need by surveying regionserver UIs; you'll see index block size accounted near the
+           top of the webpage).</para>
+         </section>
       </section>
       
       </section> <!--  important config -->