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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4344) Persist memstoreTS to disk
Date Wed, 21 Sep 2011 21:19:09 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4344?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13109877#comment-13109877
] 

Lars Hofhansl commented on HBASE-4344:
--------------------------------------

TestSeekTo fails because HFileReaderV2.ScannerV2.getFirstKeyInBlock(...) does not honor includeMemstoreTS.
Needs to be checked like this:

{code}
    private ByteBuffer getFirstKeyInBlock(HFileBlock curBlock) {
      ByteBuffer buffer = curBlock.getBufferWithoutHeader();
      // It is safe to manipulate this buffer because we own the buffer object.
      buffer.rewind();
+     if (((HFileReaderV2)this.reader).includeMemstoreTS()) {
+       buffer.getLong(); // skip memstoreTS
+     }
      int klen = buffer.getInt();
      buffer.getInt();
      ByteBuffer keyBuff = buffer.slice();
      keyBuff.limit(klen);
      keyBuff.rewind();
      return keyBuff;
    }
{code}

> 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-v2.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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