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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8701) distributedLogReplay need to apply wal edits in the receiving order of those edits
Date Wed, 18 Dec 2013 23:18:08 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8701?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13852282#comment-13852282
] 

stack commented on HBASE-8701:
------------------------------

It will be odd if this feature is enable when hfilev3 is enabled.  It will be unexpected.
 Since hfilev3 will not be on by default in 0.98, but it will be in trunk, this facility should
probably go the same route.  Otherwise +1 [~jeffreyz]

> distributedLogReplay need to apply wal edits in the receiving order of those edits
> ----------------------------------------------------------------------------------
>
>                 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
>             Fix For: 0.98.0
>
>         Attachments: 8701-v3.txt, hbase-8701-tag-v1.patch, hbase-8701-tag-v2.patch, hbase-8701-tag.patch,
hbase-8701-v4.patch, hbase-8701-v5.patch, hbase-8701-v6.patch, hbase-8701-v7.patch, hbase-8701-v8.patch
>
>
> 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(proposed by Ted) I'd like to use:
> a) During replay, we pass original wal sequence number of each edit to the receiving
RS
> b) In receiving RS, we store negative original sequence number of wal edits into mvcc
field of KVs of wal edits
> c) Add handling of negative MVCC in KVScannerComparator and KVComparator   
> d) In receiving RS, write original sequence number into an optional field of wal file
for chained RS failure situation 
> e) When opening a region, we add a safety bumper(a large number) in order for the new
sequence number of a newly opened region not to collide with old sequence numbers. 
> In the future, when we stores sequence number along with KVs, we can adjust the above
solution a little bit by avoiding to overload MVCC field.
> 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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