[jira] [Created] (HBASE-8701) distributedLogReplay need to apply wal edits in the receiving order of those eidts

["Jeffrey Zhong (JIRA)" <ji...@apache.org>]

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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