0.20: Block lost when multiple DNs trying to recover it to different genstamps
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Key: HDFS-1260
URL: https://issues.apache.org/jira/browse/HDFS-1260
Project: Hadoop HDFS
Issue Type: Bug
Affects Versions: 0.20-append
Reporter: Todd Lipcon
Assignee: Todd Lipcon
Priority: Critical
Fix For: 0.20-append
Saw this issue on a cluster where some ops people were doing network changes
without shutting down DNs first. So, recovery ended up getting started at
multiple different DNs at the same time, and some race condition occurred that
caused a block to get permanently stuck in recovery mode. What seems to have
happened is the following:
- FSDataset.tryUpdateBlock called with old genstamp 7091, new genstamp 7094,
while the block in the volumeMap (and on filesystem) was genstamp 7093
- we find the block file and meta file based on block ID only, without
comparing gen stamp
- we rename the meta file to the new genstamp _7094
- in updateBlockMap, we do comparison in the volumeMap by oldblock *without*
wildcard GS, so it does *not* update volumeMap
- validateBlockMetaData now fails with "blk_7739687463244048122_7094 does not
exist in blocks map"
After this point, all future recovery attempts to that node fail in
getBlockMetaDataInfo, since it finds the _7094 gen stamp in getStoredBlock
(since the meta file got renamed above) and then fails since _7094 isn't in
volumeMap in validateBlockMetadata
Making a unit test for this is probably going to be difficult, but doable.
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