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From "Ted Yu (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5778) Turn on WAL compression by default
Date Fri, 13 Apr 2012 05:33:48 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5778?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13253127#comment-13253127
] 

Ted Yu commented on HBASE-5778:
-------------------------------

The remaining issue is about how the replication sink correctly decompresses WAL.
>From test output, I saw:
{code}
java.io.EOFException
  at java.io.DataInputStream.readFully(DataInputStream.java:180)
  at org.apache.hadoop.hbase.KeyValue.readFields(KeyValue.java:2243)
  at org.apache.hadoop.hbase.KeyValue.readFields(KeyValue.java:2249)
  at org.apache.hadoop.hbase.regionserver.wal.WALEdit.readFields(WALEdit.java:129)
  at org.apache.hadoop.hbase.regionserver.wal.HLog$Entry.readFields(HLog.java:1700)
{code}
For replication sink, there is no CompressionContext in HLog$Entry which can be used to perform
decompression.

I agree the change should be reverted.
                
> 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: Lars Hofhansl
>            Priority: Blocker
>             Fix For: 0.94.0, 0.96.0
>
>         Attachments: 5778-addendum.txt, 5778.addendum, 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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