*: support savepoint in transaction

[crazycs520]

What problem does this PR solve?

Issue Number: close #6840

What is changed and how it works?

test> begin;
Query OK, 0 rows affected
Time: 0.000s
test> insert into t values (1);
Query OK, 1 row affected
Time: 0.001s
test> savepoint s1;
Query OK, 0 rows affected
Time: 0.001s
test> insert into t values (2);
Query OK, 1 row affected
Time: 0.001s
test> select * from t;
+---+
| a |
+---+
| 1 |
| 2 |
+---+
2 rows in set
Time: 0.007s
test> rollback to s1;
Query OK, 0 rows affected
Time: 0.000s
test> commit;
Query OK, 0 rows affected
Time: 0.001s
test> select * from t;
+---+
| a |
+---+
| 1 |
+---+
1 row in set

Related PR: tikv/client-go#490

Check List

Tests

• Unit test
• Integration test

Documentation

• Contains syntax changes

Release note

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

Support savepoint in transaction.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• ekexium
• lcwangchao
• you06

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/7956fb721906b363c02dbd0bc843d513304dfcff

[cfzjywxk]

The cleanup method would discard all the binlog mutations later. It's better to add comments to remind about it because it's not restored as other fields.

[cfzjywxk]

Besides, there're still some transaction-related states or caches in tikvTxn and KVTxn, some of them could be affected by transaction executions. I'm not quite sure about the risks if they are not considered by the rollback process.

[crazycs520]

txn.cleanup will only clean the binlog which is generated in current statement. for rollback to savepoint statement, the txn.mutations will always be nil. So txn.cleanup won't clear the old binlog.

But in another way, when binlog is enabled, execute savepoint statement will return an error.

[crazycs520]

I have verified tikvTxn and tikv.KVTxn, there are not any other fields that need to be rollback.

[cfzjywxk]

Got, maybe we need to add some defensive checks or tests in case some staging states are added in the future but they are not restored.

[bb7133]

I don't think it's a good practice to introduce more tikv interface in kv package, all interfaces should be abstracted.

But since we have such cases already like:

tidb/kv/kv.go

Line 436 in 7f023bd

Begin(opts ...tikv.TxnOption) (Transaction, error)

We don't have to solve it in this PR.

[bb7133]

LGTM

[bb7133]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: dbe4831

[crazycs520]

/run-all-tests

[crazycs520]

/run-realtikv-test

[crazycs520]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 7956fb7

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! [1] CI still failing after this pr merged.
These failed integration tests don't seem to be introduced by the current PR.

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/integration-ddl-test	🔴 failed 2, success 4, total 6	10 min	Existing failure
idc-jenkins-ci/integration-cdc-test	🟢 all 35 tests passed	35 min	Existing passed
idc-jenkins-ci-tidb/integration-common-test	🟢 all 11 tests passed	17 min	Existing passed
idc-jenkins-ci-tidb/common-test	🟢 all 12 tests passed	10 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	6 min 11 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	6 min 11 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	6 min 3 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	5 min 12 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	3 min 3 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed

[breezewish]

Just curious, how is the behavior when involving with TiDB Binlog and TiCDC? For example, what will happen for the following SQL statements (the result is MySQL's output):

CREATE TABLE t_test (id INT NOT NULL PRIMARY KEY) ENGINE=InnoDB;

START TRANSACTION;

INSERT
INTO    t_test
VALUES  (1);

SELECT  *
FROM    t_test;

 id
---
  1

SAVEPOINT tran2;

INSERT
INTO    t_test
VALUES  (2);

SELECT  *
FROM    t_test;

 id
---
  1
  2

ROLLBACK TO tran2;

SELECT  *
FROM    t_test;

 id
---
  1

ROLLBACK;

SELECT  *
FROM    t_test;

 id
---

(Source: https://stackoverflow.com/questions/1306869/are-nested-transactions-allowed-in-mysql)