ddl: use the correct timezone to encode record for adding index (#46055)

[ti-chi-bot]

This is an automated cherry-pick of #46055

What problem does this PR solve?

Issue Number: close #46033

Problem Summary:

Normally, TiDB converts timestamp values to UTC before writing them to the storage, and converts them back when reading. For adding index, we

1. Read the table records from storage.
2. Encode the index records.
3. Write/Ingest the index records to storage.

In step 1, the datum returned by extractDatumByOffsets() is in UTC timezone. It is converted to UTC again in step 2. As a result, index timestamp is converted twice.

Unistore DAG request decoding:

tidb/store/mockstore/unistore/cophandler/cop_handler.go

Lines 298 to 308 in 3846e80

	switch dagReq.TimeZoneName {
	case "":
	sc.TimeZone = time.FixedZone("UTC", int(dagReq.TimeZoneOffset))
	case "System":
	sc.TimeZone = time.Local
	default:
	sc.TimeZone, err = time.LoadLocation(dagReq.TimeZoneName)
	if err != nil {
	return nil, nil, errors.Trace(err)
	}
	}

TiKV DAG request decoding:
https://github.com/tikv/tikv/blob/14dd8cce96e064a029e58de8cf832c35d44e09a5/components/tidb_query_datatype/src/expr/ctx.rs#L86-L94

For Unistore and TiKV, the time zone name is always considered first, and the time zone offset second.

Thus, the way to buildDAGPB is wrong:

tidb/ddl/index_cop.go

Line 487 in 3846e80

dagReq.TimeZoneName, dagReq.TimeZoneOffset = timeutil.Zone(sCtx.GetSessionVars().Location())

We assigned both name and offset to UTC and -0600 respectively. UTC is kept but -0600 is discarded during parsing the DAG request.

What is changed and how it works?

Assign the time zone offset in buildDAGPB, and leave time zone name to be empty.

// Zone computes the time zone in effect at time t, returning the abbreviated
// name of the zone (such as "CET") and its offset in seconds east of UTC.
func (t Time) Zone() (name string, offset int) {
	name, offset, _, _, _ = t.loc.lookup(t.unixSec())
	return
}

Check List

Tests

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

[zimulala]

Why do we only need to change 'TimeZoneName' and not 'TimeZoneOffset'?

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-6.5@4e6af00). Click here to learn what that means.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-6.5     #46104   +/-   ##
================================================
  Coverage               ?   74.3184%           
================================================
  Files                  ?       1084           
  Lines                  ?     353658           
  Branches               ?          0           
================================================
  Hits                   ?     262833           
  Misses                 ?      74377           
  Partials               ?      16448           

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: wjhuang2016, zimulala

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [wjhuang2016,zimulala]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-15 12:15:15.18418585 +0000 UTC m=+633279.733201831: ☑️ agreed by zimulala.
• 2023-08-16 05:53:32.635092147 +0000 UTC m=+696777.184108119: ☑️ agreed by wjhuang2016.

[hawkingrei]

/retest

[tangenta]

/retest

[HuSharp]

/retest-required