ddl: make concurrent ingest job queue instead of fallback (#48645)

[ti-chi-bot]

This is an automated cherry-pick of #48645

What problem does this PR solve?

Issue Number: close #47758

Problem Summary:

1. only 1 ddl job can use ingest model and global sort.
2. another add index job using txn merge.

What is changed and how it works?

• This PR fixes problem 2 by making the concurrent adding index job queue.
• Remove useless code.
• Refactor improper usage of system variable.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  Add time.Sleep(20*time.Second) to the first phase of onCreateIndex().
  Session 1:

  mysql> alter table t add index i1 (a);
  Query OK, 0 rows affected (27.02 sec)
  

  Session 2:

  mysql> alter table t add index i2 (b);
  Query OK, 0 rows affected (46.31 sec)
  mysql> admin show ddl jobs 2;
  +--------+---------+------------+------------------------+--------------+-----------+----------+-----------+---------------------+---------------------+---------------------+--------+
  | JOB_ID | DB_NAME | TABLE_NAME | JOB_TYPE               | SCHEMA_STATE | SCHEMA_ID | TABLE_ID | ROW_COUNT | CREATE_TIME         | START_TIME          | END_TIME            | STATE  |
  +--------+---------+------------+------------------------+--------------+-----------+----------+-----------+---------------------+---------------------+---------------------+--------+
  |    110 | test    | t          | add index /* ingest */ | public       |         2 |      104 |         3 | 2023-11-16 16:47:15 | 2023-11-16 16:47:38 | 2023-11-16 16:48:01 | synced |
  |    109 | test    | t          | add index /* ingest */ | public       |         2 |      104 |         3 | 2023-11-16 16:47:14 | 2023-11-16 16:47:14 | 2023-11-16 16:47:38 | synced |
  +--------+---------+------------+------------------------+--------------+-----------+----------+-----------+---------------------+---------------------+---------------------+--------+
  2 rows in set (0.00 sec)
  

  Both jobs can use ingest now. You can also check the log:

  [2023/11/16 16:47:15.427 +08:00] [INFO] [backend_mgr.go:79] ["ingest backfill worker is already in used by another DDL job"] [category=ddl-ingest] ["processing job ID"=109]
  

• 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

[GMHDBJD]

LGTM

[tangenta]

/retest

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-7.5@b14df20). Click here to learn what that means.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #48739   +/-   ##
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  Coverage               ?   71.9694%           
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  Files                  ?       1400           
  Lines                  ?     406549           
  Branches               ?          0           
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  Hits                   ?     292591           
  Misses                 ?      94271           
  Partials               ?      19687           

Flag	Coverage Δ
unit	71.9694% <0.0000%> (?)

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Components	Coverage Δ
dumpling	53.9913% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.2578% <0.0000%> (?)

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-12-15 10:13:02.310369354 +0000 UTC m=+610273.347596280: ☑️ agreed by GMHDBJD.
• 2023-12-18 06:47:35.90689519 +0000 UTC m=+857146.944122110: ☑️ agreed by ywqzzy.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: GMHDBJD, tangenta, ywqzzy

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Needs approval from an approver in each of these files:

• OWNERS [GMHDBJD,tangenta]
• pkg/ddl/OWNERS [tangenta,ywqzzy]
• pkg/parser/OWNERS [tangenta]

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