[jira] [Commented] (LUCENE-7897) RangeQuery optimization in IndexOrDocValuesQuery

["Adrien Grand (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-7897?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16073691#comment-16073691 ] 

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

Right, we sometimes make the wrong decision, finding the optimal threshold is hard!

For this particular query, I'm wondering that there might be another issue: does your range query match more than 50% of the index content? If yes, then LUCENE-7641 probably kicks in, which makes the scorer much cheaper to create than what IndexOrDocValuesQuery assumes. If you look at the charts at https://www.elastic.co/blog/better-query-planning-for-range-queries-in-elasticsearch, LUCENE-7641 is what makes points become fast again (faster than doc values in some cases) when the range query matches most documents of the index.

> 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
>
> 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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