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https://issues.apache.org/jira/browse/HBASE-3976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13049527#comment-13049527
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stack commented on HBASE-3976:
------------------------------
I applied v3 after looking at it but then reverted it. Its making it so we
always skip cache writing out compacted file. But by default we will skip the
cache writing the compacted file. There is also a config. for the rare case
where we actually do not want to skip writing cache -- this patch was undoing
that facility.
> Disable Block Cache On Compactions
> ----------------------------------
>
> Key: HBASE-3976
> URL: https://issues.apache.org/jira/browse/HBASE-3976
> Project: HBase
> Issue Type: Improvement
> Components: regionserver
> Affects Versions: 0.90.3
> Reporter: Karthick Sankarachary
> Assignee: Nicolas Spiegelberg
> Priority: Blocker
> Fix For: 0.90.4, 0.92.0
>
> Attachments: HBASE-3976-V3.patch, HBASE-3976-unconditional.patch,
> HBASE-3976.patch
>
>
> Is there a good reason to believe that caching blocks during compactions is
> beneficial? Currently, if block cache is enabled on a certain family, then
> every time it's compacted, we load all of its blocks into the (LRU) cache, at
> the expense of the legitimately hot ones.
> As a matter of fact, this concern was raised earlier in HBASE-1597, which
> rightly points out that, "we should not bog down the LRU with unneccessary
> blocks" during compaction. Even though that issue has been marked as "fixed",
> it looks like it ought to be reopened.
> Should we err on the side of caution and not cache blocks during compactions
> period (as illustrated in the attached patch)? Or, can we be selectively
> aggressive about what blocks do get cached during compaction (e.g., only
> cache those blocks from the recent files)?
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