[jira] [Commented] (HBASE-3433) Remove the KV copy of every KV in Scan; introduced by HBASE-3232 (why doesn't keyonlyfilter make copies rather than mutate -- HBASE-3211)?

["Lars Hofhansl (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-3433?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13148164#comment-13148164 ] 

Lars Hofhansl commented on HBASE-3433:
--------------------------------------

It makes sense for some filters to transform the KVs passed to them.

Maybe we should just formalize that:
1. add  KeyValue transform(final KeyValue)  to Filter (or better name?)
2. add call to it in ScanQueryMatcher.match()
3. add a default implementation to FilterBase that just returns the passed KV
4. implement that transform in KeyOnlyFilter (i.e. KeyOnlyFilter would do the shallow copy)

                
> 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
>            Priority: Critical
>             Fix For: 0.94.0
>
>         Attachments: 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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