expression: unify casting real to string in tidb (tikv#16975) | tidb-test=pr/2325 (#53129)

[ti-chi-bot]

This is an automated cherry-pick of #53129

What problem does this PR solve?

Issue Number: close #51109

Problem Summary:

• The default implementation about casting float32/float64 into string is supported by lib strconv. strconv use Ryu algorithm to calculate significant digits.
• TiKV use method f32::to_string & f64::to_string to implement casting real to str. It can NOT guarantee precision if the number of significant digits exceeds the upper limit (f32: 6, f64: 15).
• If don't use decimal exponent format, the size of target string might be too large.

What changed and how does it work?

Unify the behavior of converting real types to strings in tidb and tikv(tikv/tikv#16975).

• use ryu lib in tikv to implement casting real type to str type.
• if abs(num) >= 1e15 or abs(num) < 1e-15 then use decimal exponent format

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

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.

Fix the incorrect result when casting REAL type to STRING type

[solotzg]

ref tikv/tikv#17003
ref https://github.com/PingCAP-QE/tidb-test/pull/2325

[solotzg]

/cc @XuHuaiyu @wshwsh12

[solotzg]

/test mysql-test

[ti-chi-bot]

@solotzg: The specified target(s) for /test were not found.
The following commands are available to trigger required jobs:

• /test build
• /test check-dev
• /test check-dev2
• /test mysql-test
• /test unit-test

The following commands are available to trigger optional jobs:

• /test pull-br-integration-test
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Use /test all to run the following jobs that were automatically triggered:

• pingcap/tidb/release-8.1/ghpr_build
• pingcap/tidb/release-8.1/ghpr_check
• pingcap/tidb/release-8.1/ghpr_check2
• pingcap/tidb/release-8.1/ghpr_mysql_test
• pingcap/tidb/release-8.1/ghpr_unit_test

In response to this:

/test mysql-test

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[tiprow]

@solotzg: No presubmit jobs available for pingcap/tidb@release-8.1

In response to this:

/test mysql-test

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[solotzg]

/retest

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (release-8.1@a1c1451). Click here to learn what that means.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.1     #53207   +/-   ##
================================================
  Coverage               ?   71.1959%           
================================================
  Files                  ?       1465           
  Lines                  ?     421260           
  Branches               ?          0           
================================================
  Hits                   ?     299920           
  Misses                 ?     100901           
  Partials               ?      20439           

Flag	Coverage Δ
unit	71.1959% <100.0000%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9957% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	40.9738% <0.0000%> (?)

[solotzg]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: wshwsh12, XuHuaiyu

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• pkg/expression/OWNERS [XuHuaiyu]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-13 05:55:41.076494737 +0000 UTC m=+1459894.833630310: ☑️ agreed by wshwsh12.
• 2024-05-13 06:00:24.984755758 +0000 UTC m=+1460178.741891328: ☑️ agreed by XuHuaiyu.

[solotzg]

/retest