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https://issues.apache.org/jira/browse/HBASE-3976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13444264#comment-13444264
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Lars Hofhansl commented on HBASE-3976:
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In a typical read/write type load you'd want "hbase.rs.cacheblocksonwrite" on,
no?
The data in the memstore is the newest, which will typically be the most
interesting data in the future. Without "hbase.rs.cacheblocksonwrite" a
memflush will make that data cold and it needs to be loaded into the cache upon
the next set of reads.
The same is actually true (to a lesser extend) for compactions: We take the
latest data and make it cold.
"hbase.rs.cacheblocksonwrite" actually does not mean much, what writes are we
talking about?
I can see see three different options here: (1) cache on flush, (2) cache on
minor compaction, and *maybe* (3) cache on major compaction... Maybe that's
overkill (especially the last one)?
> 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: Mikhail Bautin
> Priority: Minor
> Attachments: HBASE-3976.patch, HBASE-3976-unconditional.patch,
> HBASE-3976-V3.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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