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https://issues.apache.org/jira/browse/HBASE-3976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13047823#comment-13047823
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Karthick Sankarachary commented on HBASE-3976:
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My bad. We do want to be able to cache blocks in the reader associated with the
compacted file. Moreover, we do disable caching while reading from the files
being compacted, as Nicolas pointed out.
Having said that, it looks like we're still caching blocks while writing to the
compacted file. In particular, when we create its writer in
{{Store#compactStore}}, we don't seem to be disabling the cache, as we should
be doing.
To see what I mean, please take a look at the V3 version of the patch. I
apologize in advance if this turns out to be a false alarm.
> 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: Karthick Sankarachary
> 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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