Omit maxScoreCollector for field collapsing when sort by score descending

[gaobinlong]

Description

Similar to SimpleTopDocsCollectorContext, we can omit the MaxScoreCollector when sorting by score in CollapsingTopDocsCollectorContext, this can reduce the search latency and cpu usage.

By a benchmark test against the big5 index and other indices, this change can achieve 10%-20% performance improvement in both concurrent segment search enabled and disabled.

The query DSL on big5 index is:

GET big5/_search
{
  "query": {
    "match": {
      "message": "50-136-239-27"
    }
  },
  "collapse": {
    "field": "process.name.keyword"
  }
}

, the benchmark result:

Before:

|                                        50th percentile latency | collapsing |     740.061 |     ms |
|                                        90th percentile latency | collapsing |     748.504 |     ms |
|                                        99th percentile latency | collapsing |     771.312 |     ms |
|                                      99.9th percentile latency | collapsing |     843.527 |     ms |
|                                       100th percentile latency | collapsing |     857.434 |     ms |
|                                   50th percentile service time | collapsing |     738.741 |     ms |
|                                   90th percentile service time | collapsing |     747.404 |     ms |
|                                   99th percentile service time | collapsing |     770.124 |     ms |
|                                 99.9th percentile service time | collapsing |     842.116 |     ms |
|                                  100th percentile service time | collapsing |     856.587 |     ms |


After

|                                        50th percentile latency | collapsing |     568.893 |     ms |
|                                        90th percentile latency | collapsing |     579.025 |     ms |
|                                        99th percentile latency | collapsing |      621.08 |     ms |
|                                      99.9th percentile latency | collapsing |     660.756 |     ms |
|                                       100th percentile latency | collapsing |     709.702 |     ms |
|                                   50th percentile service time | collapsing |     567.327 |     ms |
|                                   90th percentile service time | collapsing |     577.377 |     ms |
|                                   99th percentile service time | collapsing |      619.84 |     ms |
|                                 99.9th percentile service time | collapsing |      659.55 |     ms |
|                                  100th percentile service time | collapsing |     708.664 |     ms |

In addition, this PR fixes the bug that max_score is null when we have multiple sort fields and _score is used as a primary sort.

Related Issues

Resolves #19179 and partly resolves #19180.

Check List

• Functionality includes testing.
  - [ ] API changes companion pull request created, if applicable.
  - [ ] Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for 23018ff: FAILURE

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[github-actions]

❕ Gradle check result for 23018ff: UNSTABLE

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[codecov]

Codecov Report

❌ Patch coverage is 82.35294% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.87%. Comparing base (af75e0b) to head (c5b8098).
⚠️ Report is 25 commits behind head on main.

Files with missing lines	Patch %	Lines
...ensearch/search/query/TopDocsCollectorContext.java	82.35%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #19181      +/-   ##
============================================
+ Coverage     72.84%   72.87%   +0.02%     
+ Complexity    69857    69823      -34     
============================================
  Files          5674     5674              
  Lines        320901   320911      +10     
  Branches      46394    46397       +3     
============================================
+ Hits         233756   233856     +100     
+ Misses        68205    68116      -89     
+ Partials      18940    18939       -1     

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[github-actions]

❌ Gradle check result for 82eb922: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for c5b8098: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for c5b8098: SUCCESS

[gaobinlong]

@reta @kkewwei could you help to review this PR? Thanks!

[reta]

LGTM, thanks @gaobinlong