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https://issues.apache.org/jira/browse/HBASE-17339?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15783540#comment-15783540
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Eshcar Hillel edited comment on HBASE-17339 at 12/28/16 7:19 PM:
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We can use existing TRT, no need for a new one. Only need to remember the
maximal flushed TS so far and make sure the range in TRT is beyond this TS.
The protocol including step-0 is for each operation:
{code}
0. check monotonicity in all relevant stores
if monotonicity is maintained and the optimization is applicable (given list of
columns) then
1. open all relevant *memory* scanners
2. get results
ONLY if result is not complete then
3. open all scanners
4. get results
else
5. open all scanners
6. get results
{code}
possible executions are 0-1-2, 0-1-2-3-4, 0-5-6, the operation returns the
result of step 2 (access only memory) or steps 4/6 (access memory and HFiles)
was (Author: eshcar):
We can use existing TRT, no need for a new one. Only need to remember the
maximal flushed TS so far and make sure the range in TRT is beyond this TS.
The protocol including step-0 is for each step:
{code}
0. check monotonicity in all relevant stores
if monotonicity is maintained and the optimization is applicable (given list of
columns) then
1. open all relevant *memory* scanners
2. get results
ONLY if result is not complete then
3. open all scanners
4. get results
else
5. open all scanners
6. get results
{code}
possible executions are 0-1-2, 0-1-2-3-4, 0-5-6, the operation returns the
result of step 2 (access only memory) or steps 4/6 (access memory and HFiles)
> 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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