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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 23:30:26 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4344?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13112225#comment-13112225

Lars Hofhansl commented on HBASE-4344:

The problem with TestStoreFile.testCacheOnWriteEvictOnClose is that KeyValue.getLength() does
not necessarily reflect its actual size on disk any longer. The fix turns out to simple:
In TestStoreFile.writeStoreFiele:

    for (int i=numKVs;i>0;i--) {
      KeyValue kv = new KeyValue(b, b, b, i, b);
-      totalSize += kv.getLength();
+      totalSize += kv.getLength()+Bytes.SIZEOF_LONG;

But it shows a kind of "unpleasantness" of this change.

I am getting a bit weary about this change. If we cannot rely KeyValue.getLength() when it
comes to storage, what other problems are we going to run into?

> 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, 4344-v4.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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