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https://issues.apache.org/jira/browse/HBASE-8370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13693798#comment-13693798
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Varun Sharma commented on HBASE-8370:
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Here are some stats for this JIRA - I am arguing that the BlockCacheHit ratio
number reported on a region server does not mean much.
"tbl.feeds.cf.home.bt.Index.fsBlockReadCnt" : 46864,
"tbl.feeds.cf.home.bt.Index.fsBlockReadCacheHitCnt" : 46864
Index Block cache hit ratio = 100 %
"tbl.feeds.cf.home.bt.Data.fsBlockReadCacheHitCnt" : 202
"tbl.feeds.cf.home.bt.Data.fsBlockReadCnt" : 247
Data Block cache hit ratio = 82 %
Overall Cache hit ration = (46864 + 202) / (46864 + 247) = 99 %
Since Indexes are hit often, cache hits are 100 % and also # of hits is high.
The real number that we are concerned about, is 82 % which is hit rate on the
data block. However, we continue to show the # 99 % on the region server
console instead. I think we need to fix that number. Please let me know if
folks object to this ?
> 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 [email protected]
> 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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