[
https://issues.apache.org/jira/browse/HBASE-17339?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15790029#comment-15790029
]
Eshcar Hillel commented on HBASE-17339:
---------------------------------------
Thanks [~enis].
What is the advantage of checking monotonicity after getting the results (step
3 in your solution) over checking it before opening memory scanners (step 0 in
my solution)?
As I see it doing the test as the first step has at least 3 advantages:
1) we avoid opening HFile scanners when they are not needed (when the result
from memory is complete, execution 0-1-2)
2) we avoid running the speculative memory-only scan when it is clear that it
will not suffice (execution 0-5-6)
3) The solution is simpler and only requires adding a maxFlushedTS attribute to
the memstore which is updated upon a flush.
The test which checks whether the solution is complete before step 3 verifies
that there are enough versions as required by the scan for each qualifier in
the scan. If the scan does not define specific qualifiers, the optimization is
not invoked, and a full scan is executed.
Do you think there are more conditions to check?
> 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.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
