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From "Ben Maurer (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-5369) Small tweaks to reduce MapFile index size
Date Sat, 28 Feb 2009 20:46:12 GMT
Small tweaks to reduce MapFile index size
-----------------------------------------

                 Key: HADOOP-5369
                 URL: https://issues.apache.org/jira/browse/HADOOP-5369
             Project: Hadoop Core
          Issue Type: Improvement
            Reporter: Ben Maurer
         Attachments: smaller_mapfile.patch

Two minor tweaks can help reduce the memory overhead of the MapFile index a bit:

1) Because the index file is a sequence file, it's length is not known. That means the index
is built using the standard "mulitply the size of the buffer on overflow" with a factor of
3/2. With small keys, the slack in the index can be substantial. This patch has a constant
upper bound on the amount of slack allowed.

2) In block compressed map files the index file often has entries with the same offset (because
the compressed block had more than index interval keys). The entries with identical offsets
do not help MapFile do random access any faster. This patch eliminates these types of entries
from new map files, and ignores them while reading old map files. This patch greatly helped
with memory usage on a compressed hbase table.

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