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https://issues.apache.org/jira/browse/HBASE-8701?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13686885#comment-13686885
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stack commented on HBASE-8701:
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bq. The original sequence number are used to store along with KV so that no
matter how many RS failures we have during replay. The original sequence number
will be used to determine the ordering.
Sorry [~jeffreyz]. I do not get why we have to have two sequenceids in an
edit; the actual and the 'original'.
bq. We only touch mvcc field and hfile sequence id is intact.
Doesn't mvcc make it out to hfile so that when we merge it w/ the memstore
(because there was say, an ongoing scan at the time of the flush), that we
still respect whatever the mvcc was at the time and not show clients' edits
that are not meant for them?
bq. new writes with positive mvcc wins because replay writes have negative mvcc
values.
Do you mean 'replace' in the above?
bq. ....the negative mvcc number is used only to replace the default hfile
sequence id(if they're presents) to break tie.
The negative mvcc is out in the hfile occupying the sequenceid-for-the-hfile
location?
I think a test case would help.
> 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
>
>
> 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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