WIP: Proof of concept support for GET_LOCK

[morgo]

What problem does this PR solve?

Issue Number: ref #14994

Problem Summary:

This is a draft implementation for GET_LOCK / RELEASE_LOCK / RELEASE_ALL_LOCKS. It doesn't handle all corner cases yet, like deadlocks.

What is changed and how it works?

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

None

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/7bdc76b2c186b53eb2e5aa3938141b9c1cca5a05

[morgo]

/run-unit-test

[bb7133]

This implementation is great!

[yahonda]

Thanks for the great work. I have found an implementation differences between this pull request and MySQL. Lock names in TiDB is case-sensitive, while MySQL one is case insensitive.

Here are steps to reproduce.

TiDB

1. Build TiDB Server and validate the TiDB commit hash is 7bdc76b2c186b53eb2e5aa3938141b9c1cca5a05

git clone https://github.com/pingcap/tidb
cd tidb
gh pr checkout 33361
make server
./bin/tidb-server

mysql> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v6.1.0-alpha-31-g7bdc76b2c-dirty
Edition: Community
Git Commit Hash: 7bdc76b2c186b53eb2e5aa3938141b9c1cca5a05
Git Branch: get-lock
UTC Build Time: 2022-03-25 02:57:19
GoVersion: go1.16
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.00 sec)

mysql>

2. Open a new session and get an advisory lock called 'foo' all lowercase.

mysql --comments --host 127.0.0.1 --port 4000 -u root
mysql> select get_lock('foo', -1);
+---------------------+
| get_lock('foo', -1) |
+---------------------+
|                   1 |
+---------------------+
1 row in set (0.00 sec)

mysql>

3. Open another new session and get another lock called 'FOO' all uppercase

mysql --comments --host 127.0.0.1 --port 4000 -u root
mysql>  select get_lock('FOO', -1);
+---------------------+
| get_lock('FOO', -1) |
+---------------------+
|                   1 |
+---------------------+
1 row in set (0.00 sec)

mysql>

Advisory lock 'foo' and 'FOO' are handled separately.

MySQL

Tested with the same scenario with MySQL, the lock name looks case insensitive.

1. Start MySQL Server

mysql> select version();
+-----------+
| version() |
+-----------+
| 8.0.28    |
+-----------+
1 row in set (0.00 sec)

2. Open a new session get an advisory lock called 'foo' all lowercase.

mysql> select get_lock('foo', -1);
+---------------------+
| get_lock('foo', -1) |
+---------------------+
|                   1 |
+---------------------+
1 row in set (0.00 sec)

mysql>

3. Open another session and get another lock called 'FOO' all uppercase

mysql> select get_lock('FOO', -1);

It waits the lock released named 'foo', it looks like MySQL lock names are case insensitive.

[morgo]

Lock names in TiDB is case-sensitive, while MySQL one is case insensitive.

I have fixed this. PTAL again :-)

[yahonda]

Validated that the advisory lock name is case insensitive. Thanks for the fix.

mysql> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v6.1.0-alpha-32-g3ac96c310-dirty
Edition: Community
Git Commit Hash: 3ac96c310bddd3973fdf000e6f76228e01556747
Git Branch: get-lock
UTC Build Time: 2022-03-28 01:49:17
GoVersion: go1.16
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.00 sec)

mysql>

[bb7133]

This draft implementation LGTM.

[ti-chi-bot]

@morgo: PR needs rebase.

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[morgo]

I am going to close this draft for now. I opened it to prove that it is possible to get this working using pessimistic locks :-) I will clean it up and merge after the proposal has been approved.