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Date: Thu, 20 Jun 2013 15:11:21 +0000 (UTC)
From: "stack (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <JIRA.12651415.1370543927825.148969.1371741081142@arcas>
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Subject: [jira] [Commented] (HBASE-8701) distributedLogReplay need to apply
 wal edits in the receiving order of those edits
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    [ https://issues.apache.org/jira/browse/HBASE-8701?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13689316#comment-13689316 ] 

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

bq. The sequence ids of hfile are intact as before.

But some can be -ve?  So they will be out of order? (I don't see special handling in v7 -- I may have missed it).

Thanks.


> 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, 0.95.2
>
>         Attachments: 8701-v3.txt, hbase-8701-v4.patch, hbase-8701-v5.patch, hbase-8701-v6.patch, hbase-8701-v7.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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