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HDFS-7752. Improve description for "dfs.namenode.num.extra.edits.retained" and "dfs.namenode.num.checkpoints.retained" properties on hdfs-default.xml. Contributed by Wellington Chevreuil.

This commit is contained in:
Harsh J 2015-02-20 19:20:41 +05:30
parent c0d9b93953
commit b9a17909ba
2 changed files with 16 additions and 4 deletions
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5
hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
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@ -341,6 +341,11 @@ Release 2.7.0 - UNRELEASED
IMPROVEMENTS
HDFS-7752. Improve description for
"dfs.namenode.num.extra.edits.retained"
and "dfs.namenode.num.checkpoints.retained" properties on
hdfs-default.xml (Wellington Chevreuil via harsh)
HDFS-7055. Add tracing to DFSInputStream (cmccabe)
HDFS-7186. Document the "hadoop trace" command. (Masatake Iwasaki via Colin

15
hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml
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@ -852,9 +852,9 @@
<property>
<name>dfs.namenode.num.checkpoints.retained</name>
<value>2</value>
<description>The number of image checkpoint files that will be retained by
<description>The number of image checkpoint files (fsimage_*) that will be retained by
the NameNode and Secondary NameNode in their storage directories. All edit
logs necessary to recover an up-to-date namespace from the oldest retained
logs (stored on edits_* files) necessary to recover an up-to-date namespace from the oldest retained
checkpoint will also be retained.
</description>
</property>
@ -863,8 +863,15 @@
<name>dfs.namenode.num.extra.edits.retained</name>
<value>1000000</value>
<description>The number of extra transactions which should be retained
beyond what is minimally necessary for a NN restart. This can be useful for
audit purposes or for an HA setup where a remote Standby Node may have
beyond what is minimally necessary for a NN restart.
It does not translate directly to file's age, or the number of files kept,
but to the number of transactions (here "edits" means transactions).
One edit file may contain several transactions (edits).
During checkpoint, NameNode will identify the total number of edits to retain as extra by
checking the latest checkpoint transaction value, subtracted by the value of this property.
Then, it scans edits files to identify the older ones that don't include the computed range of
retained transactions that are to be kept around, and purges them subsequently.
The retainment can be useful for audit purposes or for an HA setup where a remote Standby Node may have
been offline for some time and need to have a longer backlog of retained
edits in order to start again.
Typically each edit is on the order of a few hundred bytes, so the default