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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2531) FieldComparator.TermOrdValComparator compares by value unnecessarily
Date Sun, 11 Jul 2010 00:20:49 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2531?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12887126#action_12887126
] 

Michael McCandless commented on LUCENE-2531:
--------------------------------------------

I hear you; this stuff is kinda hairy ;)

The usage of reverse (and, sortPos) was only in dead code, inside the convert method.

The convert method used to be used more often (to do on-demand convert of the ord when its
readerGen != current one), but we stopped doing that and only convert the bottom slot now,
which mean this if:

{noformat}
      if (sortPos == 0 && bottomSlot != -1 && bottomSlot != slot) {
{noformat}

Can never be true (bottomSlot is *always* == slot), so that true clause was all dead code
anyway.

> FieldComparator.TermOrdValComparator compares by value unnecessarily
> --------------------------------------------------------------------
>
>                 Key: LUCENE-2531
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2531
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>            Reporter: Michael McCandless
>            Priority: Minor
>             Fix For: 3.1, 4.0
>
>         Attachments: LUCENE-2504-3x.patch, LUCENE-2504.patch, LUCENE-2531-3x.patch, LUCENE-2531.patch
>
>
> Digging on LUCENE-2504, I noticed that TermOrdValComparator's compareBottom method falls
back on compare-by-value when it needn't.
> Specifically, if we know the current bottom ord "matches" the current segment, we can
skip the value comparison when the ords are the same (ie, return 0) because the ords are exactly
comparable.
> This is hurting string sort perf especially for optimized indices (and also unoptimized
indices), and especially for highly redundant (not many unique values) fields.  This affects
all releases >= 2.9.x, but trunk is likely more severely affected since looking up a value
is more costly.

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