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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4344) Persist memstoreTS to disk
Date Sun, 25 Sep 2011 19:12:26 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4344?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13114332#comment-13114332

Ted Yu commented on HBASE-4344:

>From Amit:
  Earlier, before this patch, the essential ACID violation was occuring because some updates
that are *newer* than the Scan's read point got included into the return because flush+read
allowed them to be considered old.

 I don't see that problem anymore. 

 The current violation for ACID semantics seems from the fact that some updates that *should*
included in the return (because the readPoint is further) are not being included. Looks like
is some compactions going on, during the run, and I need to investigate to see if somehow
updateReaders etc is not including a file that needs to be included.

So the patch is not ready for integration yet.

> Persist memstoreTS to disk
> --------------------------
>                 Key: HBASE-4344
>                 URL: https://issues.apache.org/jira/browse/HBASE-4344
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Amitanand Aiyer
>            Assignee: Amitanand Aiyer
>             Fix For: 0.89.20100924
>         Attachments: 4344-v10.txt, 4344-v11.txt, 4344-v2.txt, 4344-v4.txt, 4344-v5.txt,
4344-v6.txt, 4344-v7.txt, 4344-v8.txt, 4344-v9.txt, patch-2
> Atomicity can be achieved in two ways -- (i) by using  a multiversion concurrency system
(MVCC), or (ii) by ensuring that "new" writes do not complete, until the "old" reads complete.
> Currently, Memstore uses something along the lines of MVCC (called RWCC for read-write-consistency-control).
But, this mechanism is not incorporated for the key-values written to the disk, as they do
not include the memstore TS.
> Let us make the two approaches be similar, by persisting the memstoreTS along with the
key-value when it is written to the disk.

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