session: make TxnInfo() return even if process info is empty (#57044)

[ti-chi-bot]

This is an automated cherry-pick of #57044

What problem does this PR solve?

Issue Number: close #57043

Problem Summary:

tidb/pkg/session/session.go

Lines 4026 to 4030 in c240fdf

	txnInfo := tmp.TxnInfo()
	if txnInfo != nil {
	startTS = txnInfo.StartTS
	processInfoID = txnInfo.ConnectionID
	}

TxnInfo() could be nil if process info is not set(see the implementation of TxnInfo()). Such sessions are commonly used in DDL/DXF:

tidb/pkg/ddl/backfilling_operators.go

Lines 533 to 539 in c240fdf

	sessCtx, err := w.sessPool.Get()
	if err != nil {
	logutil.Logger(w.ctx).Error("tableScanWorker get session from pool failed", zap.Error(err))
	w.ctx.onError(err)
	return
	}
	w.se = session.NewSession(sessCtx)

And they only invoke session.Begin() before using:

tidb/pkg/ddl/index_cop.go

Lines 43 to 48 in c240fdf

	func wrapInBeginRollback(se *sess.Session, f func(startTS uint64) error) error {
	err := se.Begin(context.Background())
	if err != nil {
	return errors.Trace(err)
	}
	defer se.Rollback()

As a result, the startTS from internal DDL sessions will not be reported to etcd, and GC safepoint will be advanced unexpectedly.

What changed and how does it work?

Make TxnInfo() return even if process info is empty.

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.

None

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick:

1. It must be approved by the approvers firstly.
2. AFTER it has been approved by approvers, please wait for the cherry-pick merging approval from triage owners.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign gmhdbjd for approval. For more information see the Code Review Process.

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

Needs approval from an approver in each of these files:

• OWNERS
• pkg/ddl/OWNERS
• pkg/domain/OWNERS
• pkg/infoschema/OWNERS

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]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-unit-test-ddlv1	b49c10b	link	true	/test pull-unit-test-ddlv1
idc-jenkins-ci-tidb/check_dev	b49c10b	link	true	/test check-dev

Full PR test history. Your PR dashboard.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[codecov]

Codecov Report

Attention: Patch coverage is 89.79592% with 5 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.5@5518942). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #57161   +/-   ##
================================================
  Coverage               ?   55.9763%           
================================================
  Files                  ?       1778           
  Lines                  ?     634990           
  Branches               ?          0           
================================================
  Hits                   ?     355444           
  Misses                 ?     255297           
  Partials               ?      24249           

Flag	Coverage Δ
integration	23.0424% <40.8163%> (?)
unit	72.4896% <89.7959%> (?)

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

Components	Coverage Δ
dumpling	52.9478% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	52.6611% <0.0000%> (?)