Zhihong Yu commented on HBASE-5778:

I think ReplicationSource now has the additional responsibility of shipping 
dictionaries to replication sink.
We just need to find a clean way of exposing 
SequenceFileLogWriter.compressionContext to ReplicationSource.
> 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: 0.96.0, 0.94.1
>         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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