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From "Adrien Grand (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-7897) RangeQuery optimization in IndexOrDocValuesQuery
Date Mon, 07 Aug 2017 08:41:00 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-7897?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16116270#comment-16116270
] 

Adrien Grand commented on LUCENE-7897:
--------------------------------------

Thanks for checking! The opt implementation changed because before we only knew about whether
random or sequential access was required. So we tried to use random access for the most costly
scorers since they would be unlikely to drive iteration for the MinShouldMatchScorer. The
priority queue was used to select those most costly scorers. Now that we know about the lead
cost, we can just use random access for clauses that have a 8x higher cost and sequential
access otherwise. We will still be more likely to random access on the most costly clauses
than on the least costly ones, but in a safer way.

> RangeQuery optimization in IndexOrDocValuesQuery 
> -------------------------------------------------
>
>                 Key: LUCENE-7897
>                 URL: https://issues.apache.org/jira/browse/LUCENE-7897
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: core/search
>    Affects Versions: trunk, 7.0
>            Reporter: Murali Krishna P
>         Attachments: LUCENE-7897.patch
>
>
> For range queries, Lucene uses either Points or Docvalues based on cost estimation (https://lucene.apache.org/core/6_5_0/core/org/apache/lucene/search/IndexOrDocValuesQuery.html).
Scorer is chosen based on the minCost here: https://github.com/apache/lucene-solr/blob/master/lucene/core/src/java/org/apache/lucene/search/Boolean2ScorerSupplier.java#L16
> However, the cost calculation for TermQuery and IndexOrDocvalueQuery seems to have same
weightage. Essentially, cost depends upon the docfreq in TermDict, number of points visited
and number of docvalues. In a situation where docfreq is not too restrictive, this is lot
of lookups for docvalues and using points would have been better.
> Following query with 1M matches, takes 60ms with docvalues, but only 27ms with points.
If I change the query to "message:*", which matches all docs, it choses the points(since cost
is same), but with message:xyz it choses docvalues eventhough doc frequency is 1million which
results in many docvalue fetches. Would it make sense to change the cost of docvalues query
to be higher or use points if the docfreq is too high for the term query(find an optimum threshold
where points cost < docvalue cost)?
> {noformat}
> {
>   "query": {
>     "bool": {
>       "must": [
>         {
>           "query_string": {
>             "query": "message:xyz"
>           }
>         },
>         {
>           "range": {
>             "@timestamp": {
>               "gte": 1498652400000,
>               "lte": 1498905000000,
>               "format": "epoch_millis"
>             }
>           }
>         }
>       ]
>     }
>   }
> }
> {noformat}



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