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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5778) Turn on WAL compression by default
Date Thu, 13 Dec 2012 19:34:14 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5778?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13531371#comment-13531371
] 

stack commented on HBASE-5778:
------------------------------

On commit fix this comment:

"+   * Get a reader for the WAL. If you are reading from a file that's being written to
+   * and need to reopen it multiple times, use {@link HLog.Reader#reset()} instead of this
method
+   * then just seek back to the last known good position."

It has too much about the implementation... 

This comment on reset is good... maybe use some of it:

+    // Resetting the reader lets us see newly added data if the file is being written to
+    // We also keep the same compressionContext which was previously populated for this file


Or the stuff in openReader is good.... too... makes sense

+1 on commit
                
> Turn on WAL compression by default
> ----------------------------------
>
>                 Key: HBASE-5778
>                 URL: https://issues.apache.org/jira/browse/HBASE-5778
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Jean-Daniel Cryans
>            Assignee: Jean-Daniel Cryans
>            Priority: Blocker
>             Fix For: 0.96.0
>
>         Attachments: 5778.addendum, 5778-addendum.txt, HBASE-5778-0.94.patch, HBASE-5778-0.94-v2.patch,
HBASE-5778-0.94-v3.patch, HBASE-5778-0.94-v4.patch, HBASE-5778-0.94-v5.patch, HBASE-5778.patch
>
>
> I ran some tests to verify if WAL compression should be turned on by default.
> For a use case where it's not very useful (values two order of magnitude bigger than
the keys), the insert time wasn't different and the CPU usage 15% higher (150% CPU usage VS
130% when not compressing the WAL).
> When values are smaller than the keys, I saw a 38% improvement for the insert run time
and CPU usage was 33% higher (600% CPU usage VS 450%). I'm not sure WAL compression accounts
for all the additional CPU usage, it might just be that we're able to insert faster and we
spend more time in the MemStore per second (because our MemStores are bad when they contain
tens of thousands of values).
> Those are two extremes, but it shows that for the price of some CPU we can save a lot.
My machines have 2 quads with HT, so I still had a lot of idle CPUs.

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