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https://issues.apache.org/jira/browse/HBASE-29398?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Viraj Jasani resolved HBASE-29398.
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Fix Version/s: 3.0.0-beta-2
Hadoop Flags: Reviewed
Resolution: Fixed
> Server side scan metrics for bytes read from FS vs Block cache vs memstore
> --------------------------------------------------------------------------
>
> Key: HBASE-29398
> URL: https://issues.apache.org/jira/browse/HBASE-29398
> Project: HBase
> Issue Type: Improvement
> Reporter: Sanjeet Malhotra
> Assignee: Sanjeet Malhotra
> Priority: Major
> Labels: pull-request-available
> Fix For: 3.0.0-beta-2
>
>
> Currently, HBase doesn't have a metric on the server side which counts how
> many bytes were read from FS vs block cache vs memstore. Reading cells from
> in-memory like block cache or memstore vs from FS can make latencies vary
> drastically.
> Separate metrics for bytes scanned from block cache vs memstore are
> beneficial for use cases which immediately read (like within 5 sec) after
> writing the data. There the expectation would be that bytes scanned from FS
> or block cache should be negligible unless a flush happened (which can be
> checked from logs) or cache on write is enabled.
> Currently, HBase has a server side scan metric `countOfBlockBytesScanned`
> which aims to capture the block bytes scanned by read request. But it doesn't
> capture:
> * Block bytes scanned as part of KeyValueHeap#pollRealKV(). So, we could end
> up scanning a lot of excess HFiles in case when scanner at the top of heap
> hasn't done a real seek and the row might get returned from memstore. In this
> case the block I/O done in scanning excess HFile won't be accounted in any
> metrics.
> * Index block bytes scanned, bloom filter bytes scanned.
> * Difference between bytes scanned from block cache vs FS.
> The proposal is to add 3 new server side scan metrics, one each for: bytes
> scanned from FS, bytes scanned from block cache and bytes scanned from
> memstore.
>
> I intend to cherry-pick this change to HBase 3 and HBase 2 (till HBase 2.5).
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