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https://issues.apache.org/jira/browse/HBASE-8701?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13688954#comment-13688954
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Jeffrey Zhong commented on HBASE-8701:
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Thanks [[email protected]] for the comments.
{quote}
How will compactions deal with the -ve sequenceid
{quote}
The sequence ids of hfile are intact as before.
{quote}
Sometimes its a boolean and other times its a ts?
{quote}
decodeMemstoreTS is boolean. It's used to indicate hfilereader whether to
decode memtoreTS(mvcc) number. An existing optimization to skip mvcc number
decoding by using the following logic. Since we use negative mvcc, the
optimization may skip decode mvcc number from a hfile.
{code}
Bytes.toLong(fileInfo.get(HFileWriterV2.MAX_MEMSTORE_TS_KEY)) > 0;
{code}
{quote}
Regards 200M.
{quote}
This part will be updated later by 8741. I left the code there is to let one of
my new test case pass where we test same version update comes during recovery.
{quote}
Is that safe presumption to make in replay?
Is this the least sequenceid of the batch?
Again, what is the difference between these two sequenceids?
Do we have to add it to WALEdit at all?
{quote}
I think we may not need the origSequneceNumber because mvcc is part of KV and
should be already written into WAL? Let me try to see if I can cut the
origSequenceNumber.
{quote}
Is this 'if it is present'?
{quote}
Yes.
{quote}
We only do this stuff for Puts and Deletes? Don't we have other types out in
the WAL?
{quote}
Only puts and deletes are used for recovery purpose in WAL.
> 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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