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Varun Sharma commented on HBASE-8370: ------------------------------------- "We don't have per block type metrics in trunk/95 because the overall cache hit percentage is a good proxy for data block cache percent. Yes the overall number is higher but it still gives a good actionable number. You can know if you're doing better or worse than you were before. Even better is the derivative of cache miss count." I am not sure this is true - this number is always 99 % for us on all clusters - blockCacheHitCachingRation - how can a number which never changes, ever be actionable ? Even with decimal numbers, its never going to change because the index blocks are going to take over Also, the different b/w 82 % cache hit ratio to 99 % cache hit ratio is enormous. Controlling you p80 on latency is a *lot* easier than your p99. A cache hit ratio of 99 % just sends you this false sense of security that you have controlled your p99 latency. This is important for online serving, maynot be for enterprise. I guess, we don't need to bring back SchemaMetrics to fix this but we can have block level metrics. At least I want to be sure that Index blocks have 100 % cache hit rates because if that's not happening, then I am in a bad situation. It would be better to not have folks using HBase for online storage, play a guessing game, as to what the true effectiveness of the cache is. > 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 d...@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. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira