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https://issues.apache.org/jira/browse/HBASE-7051?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13484803#comment-13484803
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ramkrishna.s.vasudevan commented on HBASE-7051:
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Yes.. what Gregory says is possible.. i tried to reproduce this scenario that
he mentioned. It happens..
So if thread B is just before waiting for MVCC to complete and by the time of
thread A does the check operation it is going to succeed.
Now the MVCC completes and the put as part of checkAndPut gets completed thus
overwriting what the thread B has written.
> Read/Updates (increment,checkAndPut) should properly read MVCC
> --------------------------------------------------------------
>
> Key: HBASE-7051
> URL: https://issues.apache.org/jira/browse/HBASE-7051
> Project: HBase
> Issue Type: Bug
> Affects Versions: 0.96.0
> Reporter: Gregory Chanan
>
> See, for example:
> {code}
> // TODO: Use MVCC to make this set of increments atomic to reads
> {code}
> Here's an example of what I can happen (would probably be good to write up a
> test case for each read/update):
> Concurrent update via increment and put.
> The put grabs the row lock first and updates the memstore, but releases the
> row lock before the MVCC is advanced. Then, the increment grabs the row lock
> and reads right away, reading the old value and incrementing based on that.
> There are a few options here:
> 1) Waiting for the MVCC to advance for read/updates: the downside is that you
> have to wait for updates on other rows.
> 2) Have an MVCC per-row (table configuration): this avoids the unnecessary
> contention of 1)
> 3) Transform the read/updates to write-only with rollup on read.. E.g. an
> increment would just have the number of values to increment.
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