A partial rollback cause the new changes done after upgrade to be visible after
rollback
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Key: HDFS-2017
URL: https://issues.apache.org/jira/browse/HDFS-2017
Project: Hadoop HDFS
Issue Type: Bug
Components: name-node
Affects Versions: 0.20.1
Reporter: HariSree
This is the scenario :
Namenode has 3 name dirs configured ..
1) Namenode upgrade starts - Upgrade fails after 1st directory is upgraded (2nd
and 3rd dir is left unchanged ..) { like , Namenode process down }
2) Namenode starts and new files written ..
3) Namenode shutdown and rollbacked
Since Namenode is saving the latest image dir(the upgraded 1st dir since
checkpointtime is incremented during upgrade for this dir) will be loaded and
saved to all dirs during loadfsimage ..
But if a ROLLBACK is done , the 1st dir will be rolled back (the older copy
becomes current and its checkpointtime is now LESS than other dirs ..) and
others left behind since they dont contain previous .. Now during loadfsimage ,
the 2nd dir will be selected since it has the highest checkpoint time and saved
to all dirs (including 1st ) .. Now due to this , the new changes b/w UPGRADE
and ROLLBACK present in 2nd dir gets reflected even after ROLLBACK ..
Now if we try to do a rollback again , all the previous states will be lost and
delta becomes permanent to all dirs .. and no way to go back to the PREVIOUS
STATE
This is not the case with a SUCCESSFUL Upgrade/Rollback (New changes lost after
rollback)..
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