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https://issues.apache.org/jira/browse/HBASE-18847?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16171702#comment-16171702
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Sean Busbey commented on HBASE-18847:
-------------------------------------

great find [~richhowarth]! are you interested in posting up a patch that 
refactors it out?

> Huge performance bottleneck in HFileWriterV2 in 1.2.6
> -----------------------------------------------------
>
>                 Key: HBASE-18847
>                 URL: https://issues.apache.org/jira/browse/HBASE-18847
>             Project: HBase
>          Issue Type: Bug
>          Components: Performance
>    Affects Versions: 1.2.6
>            Reporter: Rich Howarth
>
> The below code block starts at line 277 of HFileWriterV2.java. Class-level 
> synchronization in a heavily used code path has a demonstrably significant 
> negative effect on performance. I tested forcing a major compaction with 18 
> compaction threads per node; removing the synchronization resulted in an 
> order of magnitude performance increase, with the bottleneck then being at 
> the disks (where I want it to be).
> {code:java}
>     synchronized (HFileWriterV2.class) {
>       if (WARN_CELL_WITH_TAGS && getFileContext().isIncludesTags()) {
>         LOG.warn("A minimum HFile version of " + 
> HFile.MIN_FORMAT_VERSION_WITH_TAGS
>           + " is required to support cell attributes/tags. Consider setting "
>           + HFile.FORMAT_VERSION_KEY + " accordingly.");
>         WARN_CELL_WITH_TAGS = false;
>       }
>     }
> {code}



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