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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HBASE-10625) Remove unnecessary key compare from AbstractScannerV2.reseekTo
Date Thu, 27 Feb 2014 20:22:22 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13915006#comment-13915006
] 

Lars Hofhansl edited comment on HBASE-10625 at 2/27/14 8:22 PM:
----------------------------------------------------------------

bq. Test with adjacent cols like 4th and 5th?
Did that, it is still faster, but to a lesser degree.

(In the end, the best solution here would be to only (re)seek when we can expect the KV we're
looking for to be in another HFile block, otherwise do a series of next calls. I have not
found a clean way, yet, of doing that.)

I will report numbers for my work and home machines in a bit, then we can decide whether the
change is worth it.


was (Author: lhofhansl):
bq. Test with adjacent cols like 4th and 5th?
Did that, it is still faster, but to a lesser degree.

(In the end, the best solution here would be to only (re)seek when we can expect the KV we're
looking for to be in another HFile block, otherwise do a series of next calls. I have not
found a clean way, yet, of doing that.)


> Remove unnecessary key compare from AbstractScannerV2.reseekTo
> --------------------------------------------------------------
>
>                 Key: HBASE-10625
>                 URL: https://issues.apache.org/jira/browse/HBASE-10625
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>         Attachments: 10625-0.94.txt, 10625-trunk.txt
>
>
> In reseekTo we find this
> {code}
> ...
>         compared = compareKey(reader.getComparator(), key, offset, length);
>         if (compared < 1) {
>           // If the required key is less than or equal to current key, then
>           // don't do anything.
>           return compared;
>         } else {
>            ...
>            return loadBlockAndSeekToKey(this.block, this.nextIndexedKey,
>               false, key, offset, length, false);
> ...
> {code}
> loadBlockAndSeekToKey already does the right thing when a we pass a key that sorts before
the current key. It's less efficient than this early check, but in the vast (all?) cases we
pass forward keys (as required by the reseek contract). We're optimizing the wrong thing.
> Scanning with the ExplicitColumnTracker is 20-30% faster.
> (I tested with rows of 5 short KVs selected the 2nd and or 4th column)
> I propose simply removing that check.



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