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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4283) Support more frequent skip with Block Postings Format
Date Tue, 07 Aug 2012 21:27:10 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4283?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13430636#comment-13430636
] 

Michael McCandless commented on LUCENE-4283:
--------------------------------------------

Thanks Billy, that's a nice optimization!  I think other postings formats should do the same
thing...

It seems to give a small gain to the skip-heavy queries:
{noformat}
                Task    QPS base StdDev baseQPS nextskipStdDev nextskip      Pct diff
         AndHighHigh       23.87        0.09       23.56        0.19   -2% -    0%
              Fuzzy2       63.37        1.07       62.59        0.86   -4% -    1%
          OrHighHigh       11.67        0.08       11.53        0.35   -4% -    2%
              Fuzzy1       75.44        1.02       74.59        0.74   -3% -    1%
           OrHighMed       24.14        0.18       23.89        0.72   -4% -    2%
             Respell       62.66        0.65       62.04        1.37   -4% -    2%
           OrHighLow       27.86        0.23       27.60        0.85   -4% -    2%
    HighSloppyPhrase        2.00        0.04        1.99        0.05   -5% -    3%
        HighSpanNear        1.70        0.02        1.69        0.01   -2% -    1%
             LowTerm      517.40        1.67      514.32        2.68   -1% -    0%
     LowSloppyPhrase        7.61        0.07        7.58        0.16   -3% -    2%
     MedSloppyPhrase        6.90        0.09        6.88        0.13   -3% -    2%
            PKLookup      192.23        1.99      191.81        3.80   -3% -    2%
             Prefix3       82.35        0.63       82.36        1.06   -2% -    2%
            Wildcard       52.49        0.44       52.54        0.41   -1% -    1%
            HighTerm       36.03        0.11       36.09        0.03    0% -    0%
              IntNRQ       11.56        0.07       11.58        0.03    0% -    1%
             MedTerm      197.94        0.88      198.87        0.36    0% -    1%
         MedSpanNear        4.84        0.07        4.86        0.03   -1% -    2%
         LowSpanNear        9.49        0.26        9.64        0.01   -1% -    4%
           LowPhrase       21.95        0.38       22.39        0.08    0% -    4%
          AndHighLow      641.56       10.38      657.49        5.64    0% -    5%
           MedPhrase       13.04        0.30       13.37        0.05    0% -    5%
          AndHighMed       67.13        0.57       69.30        0.80    1% -    5%
          HighPhrase        1.81        0.10        1.87        0.03   -3% -   11%
{noformat}

                
> Support more frequent skip with Block Postings Format
> -----------------------------------------------------
>
>                 Key: LUCENE-4283
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4283
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Han Jiang
>            Priority: Minor
>         Attachments: LUCENE-4283-buggy.patch, LUCENE-4283-buggy.patch, LUCENE-4283-codes-cleanup.patch,
LUCENE-4283-record-next-skip.patch, LUCENE-4283-slow.patch, LUCENE-4283-small-interval-fully.patch,
LUCENE-4283-small-interval-partially.patch
>
>
> This change works on the new bulk branch.
> Currently, our BlockPostingsFormat only supports skipInterval==blockSize. Every time
the skipper reaches the last level 0 skip point, we'll have to decode a whole block to read
doc/freq data. Also,  a higher level skip list will be created only for those df>blockSize^k,
which means for most terms, skipping will just be a linear scan. If we increase current blockSize
for better bulk i/o performance, current skip setting will be a bottleneck. 
> For ForPF, the encoded block can be easily splitted if we set skipInterval=32*k. 

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