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https://issues.apache.org/jira/browse/HBASE-8763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13780598#comment-13780598
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Enis Soztutar commented on HBASE-8763:
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Definitely. I have a patch which works on 90% of the unit tests :) Was going to
create a RB, but never got to make it stable enough, perf test, handle old mvcc
numbers in files, etc.
The approach is that we get keep MVCC, but mvcc write number will be the log
sequence number. So instead of:
1. get mvcc number
2. memstore insert
3. append no sync
4. sync
we are doing:
1. append no sync
2. memstore insert
3. sync
You can check the TrxManager, which keeps track of on the fly transactions.
MVCC is an impl of TrxMngr. HLog will order the transactions by the update
lock, and create and add a trx to the Trx manager. TrxManager still ensures
that the transactions are committed (made visible) in serial order. row locking
order is also not changed, meaning, read-write transcations still have to wait
for on-flight transactions to finish, after they acquire the row locks.
> [BRAINSTORM] Combine MVCC and SeqId
> -----------------------------------
>
> Key: HBASE-8763
> URL: https://issues.apache.org/jira/browse/HBASE-8763
> Project: HBase
> Issue Type: Improvement
> Components: regionserver
> Reporter: Enis Soztutar
> Fix For: 0.98.0
>
>
> HBASE-8701 and a lot of recent issues include good discussions about mvcc +
> seqId semantics. It seems that having mvcc and the seqId complicates the
> comparator semantics a lot in regards to flush + WAL replay + compactions +
> delete markers and out of order puts.
> Thinking more about it I don't think we need a MVCC write number which is
> different than the seqId. We can keep the MVCC semantics, read point and
> smallest read points intact, but combine mvcc write number and seqId. This
> will allow cleaner semantics + implementation + smaller data files.
> We can do some brainstorming for 0.98. We still have to verify that this
> would be semantically correct, it should be so by my current understanding.
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