Jeffrey Zhong created HBASE-8701:
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Summary: distributedLogReplay need to apply wal edits in the
receiving order of those eidts
Key: HBASE-8701
URL: https://issues.apache.org/jira/browse/HBASE-8701
Project: HBase
Issue Type: Bug
Components: MTTR
Reporter: Jeffrey Zhong
Assignee: Jeffrey Zhong
This issue happens in distributedLogReplay mode when recovering multiple puts
of the same key + version(timestamp). After replay, the value is
nondeterministic of the key
h5. The original concern situation raised from [~eclark]:
For all edits the rowkey is the same.
There's a log with: [ A (ts = 0), B (ts = 0) ]
Replay the first half of the log.
A user puts in C (ts = 0)
Memstore has to flush
A new Hfile will be created with [ C, A ] and MaxSequenceId = C's seqid.
Replay the rest of the Log.
Flush
The issue will happen in similar situation like Put(key, t=T) in WAL1 and
Put(key,t=T) in WAL2
h5. Below is the option I'd like to use:
a) During replay, we pass wal file name hash in each replay batch and original
wal sequence id of each edit to the receiving RS
b) Once a wal is recovered, playing RS send a signal to the receiving RS so the
receiving RS can flush
c) In receiving RS, different WAL file of a region sends edits to different
memstores.(We can visualize this in high level as sending changes to a new
region object with name(origin region name + wal name hash) and use the
original sequence Ids.)
d) writes from normal traffic(allow writes during recovery) are put in normal
memstores as of today and flush normally with new sequenceIds.
h5. The other alternative options are listed below for references:
Option one
a) disallow writes during recovery
b) during replay, we pass original wal sequence ids
c) hold flush till all wals of a recovering region are replayed. Memstore
should hold because we only recover unflushed wal edits. For edits with same
key + version, whichever with larger sequence Id wins.
Option two
a) During replay, we pass original wal sequence ids
b) for each wal edit, we store each edit's original sequence id along with its
key.
c) during scanning, we use the original sequence id if it's present otherwise
its store file sequence Id
d) compaction can just leave put with max sequence id
Please let me know if you have better ideas.
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