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From "Varun Sharma (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8370) Report data block cache hit rates apart from aggregate cache hit rates
Date Thu, 27 Jun 2013 02:31:20 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13694433#comment-13694433
] 

Varun Sharma commented on HBASE-8370:
-------------------------------------

Also, coming back to the point about the metrics being actionable.

RE:If your bloom block cache hit count goes down you can do....... Not much. Not worth counting
if you can't take action on it.

I disagree that its not actionable. I would go fix the block cache in this case. It means
there is something seriously wrong with our implementation of the block cache if we are evicting
bloom blocks - maybe its just me but I feel we should not be evicting bloom blocks.

- If the cache hit rate is too low on Data Blocks, the action item is to increase Block Cache
amount.

I would agree that index block metrics are not needed or actionable if it is indeed the case
that we pin index blocks forever.




                
> Report data block cache hit rates apart from aggregate cache hit rates
> ----------------------------------------------------------------------
>
>                 Key: HBASE-8370
>                 URL: https://issues.apache.org/jira/browse/HBASE-8370
>             Project: HBase
>          Issue Type: Improvement
>          Components: metrics
>            Reporter: Varun Sharma
>            Assignee: Varun Sharma
>            Priority: Minor
>
> Attaching from mail to dev@hbase.apache.org
> I am wondering whether the HBase cachingHitRatio metrics that the region server UI shows,
can get me a break down by data blocks. I always see this number to be very high and that
could be exagerated by the fact that each lookup hits the index blocks and bloom filter blocks
in the block cache before retrieving the data block. This could be artificially bloating up
the cache hit ratio.
> Assuming the above is correct, do we already have a cache hit ratio for data blocks alone
which is more obscure ? If not, my sense is that it would be pretty valuable to add one.

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