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https://issues.apache.org/jira/browse/HBASE-3433?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13148797#comment-13148797
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Lars Hofhansl commented on HBASE-3433:
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I don't think the difference will be measurable, was just a shallow copy. The
point of this patch was to formalize how a filter would modify the KVs, rather
than doing it as a side-effect of the filtering methods.
I'll write a little test client, I'm willing to bet that there will no
measurable improvement. :)
> Remove the KV copy of every KV in Scan; introduced by HBASE-3232 (why doesn't
> keyonlyfilter make copies rather than mutate -- HBASE-3211)?
> ------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HBASE-3433
> URL: https://issues.apache.org/jira/browse/HBASE-3433
> Project: HBase
> Issue Type: Improvement
> Components: performance, regionserver
> Reporter: stack
> Assignee: Lars Hofhansl
> Priority: Critical
> Fix For: 0.94.0
>
> Attachments: 3433-v2.txt, 3433-v3.txt, 3433.txt,
> HBASE-3433-sidenote.patch
>
>
> Here is offending code from inside in StoreScanner#next:
> {code}
> // kv is no longer immutable due to KeyOnlyFilter! use copy for safety
> KeyValue copyKv = new KeyValue(kv.getBuffer(), kv.getOffset(),
> kv.getLength());
> {code}
> This looks wrong given philosophy up to this has been avoidance of
> garbage-making copies.
> Maybe this has been looked into before and this is the only thing to be done
> but why is KeyOnlyFilter not making copies rather than mutating originals?
> Making this critical against 0.92.
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