[jira] [Updated] (LUCENE-10542) FieldSource exists implementations can avoid value retrieval

["Kevin Risden (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCENE-10542?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kevin Risden updated LUCENE-10542:
----------------------------------
    Summary: FieldSource exists implementations can avoid value retrieval  (was: FieldSource exists implementation can avoid value retrieval)

> FieldSource exists implementations can avoid value retrieval
> ------------------------------------------------------------
>
>                 Key: LUCENE-10542
>                 URL: https://issues.apache.org/jira/browse/LUCENE-10542
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Kevin Risden
>            Assignee: Kevin Risden
>            Priority: Minor
>         Attachments: flamegraph_getValueForDoc.png
>
>          Time Spent: 0.5h
>  Remaining Estimate: 0h
>
> While looking at LUCENE-10534, found that *FieldSource exists implementation after LUCENE-7407 can avoid value lookup when just checking for exists.
> Flamegraphs - x axis = time spent as a percentage of time being profiled, y axis = stack trace bottom being first call top being last call
> Looking only at the left most getValueForDoc highlight only (and it helps to make it bigger or download the original)
> !flamegraph_getValueForDoc.png|height=410,width=1000!
> LongFieldSource#exists spends MOST of its time doing a LongFieldSource#getValueForDoc. LongFieldSource#getValueForDoc spends its time doing two things primarily:
> * FilterNumericDocValues#longValue()
> * advance()
> This makes sense based on looking at the code (copied below to make it easier to see at once) 
> https://github.com/apache/lucene/blob/main/lucene/queries/src/java/org/apache/lucene/queries/function/valuesource/LongFieldSource.java#L72
> {code:java}
>       private long getValueForDoc(int doc) throws IOException {
>         if (doc < lastDocID) {
>           throw new IllegalArgumentException(
>               "docs were sent out-of-order: lastDocID=" + lastDocID + " vs docID=" + doc);
>         }
>         lastDocID = doc;
>         int curDocID = arr.docID();
>         if (doc > curDocID) {
>           curDocID = arr.advance(doc);
>         }
>         if (doc == curDocID) {
>           return arr.longValue();
>         } else {
>           return 0;
>         }
>       }
> {code}
> LongFieldSource#exists - doesn't care about the actual longValue. Just that there was a value found when iterating through the doc values.
> https://github.com/apache/lucene/blob/main/lucene/queries/src/java/org/apache/lucene/queries/function/valuesource/LongFieldSource.java#L95
> {code:java}
>       @Override
>       public boolean exists(int doc) throws IOException {
>         getValueForDoc(doc);
>         return arr.docID() == doc;
>       }
> {code}
> So putting this all together for exists calling getValueForDoc, we spent ~50% of the time trying to get the long value when we don't need it in exists. We can save that 50% of time making exists not care about the actual value and just return if doc == curDocID basically.
> This 50% extra is exaggerated in MaxFloatFunction (and other places) since exists() is being called a bunch. Eventually the value will be needed from longVal(), but if we call exists() say 3 times for every longVal(), we are spending a lot of time computing the value when we only need to check for existence.
> I found the same pattern in DoubleFieldSource, EnumFieldSource, FloatFieldSource, IntFieldSource, LongFieldSource. I put together a change showing what this would look like:
> ----
> Simple JMH performance tests comparing the original FloatFieldSource to the new ones from PR #847.
>  
> | Benchmark                                                       | Mode  | Cnt | Score and Error  | Units |
> |-----------------------------------------------------------------|-------|-----|------------------|-------|
> | MyBenchmark.testMaxFloatFunction                                | thrpt | 25  | 64.159  ±  2.031 | ops/s |
> | MyBenchmark.testNewMaxFloatFunction                             | thrpt | 25  | 94.997  ±  2.365 | ops/s |
> | MyBenchmark.testMaxFloatFunctionNewFloatFieldSource             | thrpt | 25  | 123.191 ±  9.291 | ops/s |
> | MyBenchmark.testNewMaxFloatFunctionNewFloatFieldSource          | thrpt | 25  | 123.817 ±  6.191 | ops/s |
> | MyBenchmark.testMaxFloatFunctionRareField                       | thrpt | 25  | 244.921 ±  6.439 | ops/s |
> | MyBenchmark.testNewMaxFloatFunctionRareField                    | thrpt | 25  | 239.288 ±  5.136 | ops/s |
> | MyBenchmark.testMaxFloatFunctionNewFloatFieldSourceRareField    | thrpt | 25  | 271.521 ±  3.870 | ops/s |
> | MyBenchmark.testNewMaxFloatFunctionNewFloatFieldSourceRareField | thrpt | 25  | 279.334 ± 10.511 | ops/s |
> Source: https://github.com/risdenk/lucene-jmh



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