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https://issues.apache.org/jira/browse/HBASE-18847?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16171745#comment-16171745
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Sean Busbey commented on HBASE-18847:
-------------------------------------
looks like the synchronized block came into branch-1.2 via HBASE-15118.
the version of that fix on master and branch-1 at the time was different and
didn't include the synchronized block. From looking at the branch-1.3+
versions, they just ignore warnings and do an unsafe read/write to the static
boolean. Since we're talking about additional warning messages that's probably
fine.
> 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: Improvement
> Components: Performance
> Affects Versions: 1.2.6
> Reporter: Rich Howarth
> Priority: Critical
>
> 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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