statistics: improve memory for mergeGlobalStatsTopNByConcurrency (#45993)

[ti-chi-bot]

This is an automated cherry-pick of #45993

What problem does this PR solve?

Issue Number: close #45727

Problem Summary:

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

goos: linux
goarch: amd64
pkg: github.com/pingcap/tidb/statistics
cpu: AMD Ryzen 7 7735HS with Radeon Graphics
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size100-16         	   16852	     82494 ns/op	   19801 B/op	     248 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size1000-16        	    2394	    528919 ns/op	  164952 B/op	    2048 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size10000-16       	      46	  27104549 ns/op	16254536 B/op	  200239 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size100000-16      	       1	3820741278 ns/op	1564350080 B/op	19552007 allocs/op

after

goos: linux
goarch: amd64
pkg: github.com/pingcap/tidb/statistics
cpu: AMD Ryzen 7 7735HS with Radeon Graphics
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size100-16         	   25230	     54848 ns/op	    6234 B/op	      48 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size1000-16        	    5294	    209518 ns/op	   35425 B/op	      48 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size10000-16       	     128	   9095930 ns/op	  350648 B/op	     203 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size100000-16      	       1	1199193921 ns/op	 3448576 B/op	    1617 allocs/op

• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[hawkingrei]

/test all

[tiprow]

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In response to this:

/test all

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hi-rustin, time-and-fate

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-14 08:29:09.24249794 +0000 UTC m=+533313.791513926: ☑️ agreed by time-and-fate.
• 2023-08-14 08:41:16.424674092 +0000 UTC m=+534040.973690064: ☑️ agreed by hi-rustin.

[hawkingrei]

/retest

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-6.5@266b833). Click here to learn what that means.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-6.5     #46057   +/-   ##
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  Coverage               ?   73.7198%           
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  Files                  ?       1083           
  Lines                  ?     347517           
  Branches               ?          0           
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  Hits                   ?     256189           
  Misses                 ?      74927           
  Partials               ?      16401           

[hawkingrei]

/retest