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From "Lars Hofhansl (Commented) (JIRA)" <j...@apache.org>
Subject [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)?
Date Fri, 11 Nov 2011 19:40:51 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3433?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13148690#comment-13148690
] 

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

How's this?
{code}
  /**
   * Give the filter a chance to transform the passed KeyValue.
   * If the KeyValue is changed a new KeyValue object must be returned.
   * @see org.apache.hadoop.hbase.KeyValue#shallowCopy()
   *
   * The transformed KeyValue is what is eventually returned to the
   * client. Most filters will return the passed KeyValue unchanged.
   * @see org.apache.hadoop.hbase.filter.KeyOnlyFilter#transform(KeyValue)
   * for an example of a transformation.
   *
   * @param v the KeyValue in question
   * @return the changed KeyValue
   */
  public KeyValue transform(KeyValue v);
{code}

                
> 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.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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