[jira] [Commented] (HBASE-3976) Disable Block Cache On Compactions

["Lars Hofhansl (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-3976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13448131#comment-13448131 ] 

Lars Hofhansl commented on HBASE-3976:
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Any comment on my comment :) ?
The use case we're the most interested in is transferring the "hotness" of the memstore to the blockcache (i.e. cache on flush).
If there's interest I'll look into implementing the flags I mentioned in my previous comment.
                
> 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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