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From "Eshcar Hillel (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17339) Scan-Memory-First Optimization for Get Operation
Date Wed, 28 Dec 2016 15:11:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17339?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15783076#comment-15783076
] 

Eshcar Hillel commented on HBASE-17339:
---------------------------------------

If I understand correctly then when clients put cells into peer clusters read operations can
return different results depending on where they read from. So this is not just a problem
of this optimization.
As Phil suggested we can use the TimeRangeTracker at each store to understand whether or not
monotonicity is maintained.
We can add a step-0 where the region queries all relevant stores to determine if they all
maintain monotonicity and if so  apply the optimization.
Sounds reasonable?

I can work on a new patch that checks monotonicity before memory scan and extends conditions
to verify the result of the memory scan is complete before returning it to the user.

> Scan-Memory-First Optimization for Get Operation
> ------------------------------------------------
>
>                 Key: HBASE-17339
>                 URL: https://issues.apache.org/jira/browse/HBASE-17339
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Eshcar Hillel
>         Attachments: HBASE-17339-V01.patch
>
>
> The current implementation of a get operation (to retrieve values for a specific key)
scans through all relevant stores of the region; for each store both memory components (memstores
segments) and disk components (hfiles) are scanned in parallel.
> We suggest to apply an optimization that speculatively scans memory-only components first
and only if the result is incomplete scans both memory and disk.



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