session,expression: Support IS_USED_LOCK function

[dveeden]

What problem does this PR solve?

Issue Number: close #44493

Problem Summary:

What is changed and how it works?

TiDB, Session 1

sql> select is_used_lock('foo');
+---------------------+
| is_used_lock('foo') |
+---------------------+
|                NULL |
+---------------------+
1 row in set (0.0037 sec)

sql> select get_lock('foo', 10);
+---------------------+
| get_lock('foo', 10) |
+---------------------+
|                   1 |
+---------------------+
1 row in set (0.0032 sec)

sql> select is_used_lock('foo');
+---------------------+
| is_used_lock('foo') |
+---------------------+
|       2199023255557 |
+---------------------+
1 row in set (0.0005 sec)

sql> select connection_id();
+-----------------+
| connection_id() |
+-----------------+
|   2199023255557 |
+-----------------+
1 row in set (0.0004 sec)

TiDB, Session 2

sql> select is_used_lock('foo');
+---------------------+
| is_used_lock('foo') |
+---------------------+
|                   1 |
+---------------------+
1 row in set (1.0120 sec)

sql> select is_used_lock('bar');
+---------------------+
| is_used_lock('bar') |
+---------------------+
|                NULL |
+---------------------+
1 row in set (0.0033 sec)

MySQL

sql> select is_used_lock('foo');
+---------------------+
| is_used_lock('foo') |
+---------------------+
|                NULL |
+---------------------+
1 row in set (0.0007 sec)

sql> select get_lock('foo',10);
+--------------------+
| get_lock('foo',10) |
+--------------------+
|                  1 |
+--------------------+
1 row in set (0.0007 sec)

sql> select is_used_lock('foo');
+---------------------+
| is_used_lock('foo') |
+---------------------+
|                  36 |
+---------------------+
1 row in set (0.0007 sec)

sql> select connection_id();
+-----------------+
| connection_id() |
+-----------------+
|              36 |
+-----------------+
1 row in set (0.0006 sec)

sql> select version();
+-----------+
| version() |
+-----------+
| 8.0.33    |
+-----------+
1 row in set (0.0007 sec)

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.

Support for the `IS_USED_LOCK()` and `IS_FREE_LOCK()` functions was added

[ti-chi-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[dveeden]

The problem with the current implementation is that lock.owner is only available to the current session. For other sessions (possibly on other nodes) this basically tries to get and release a transaction to see if a lock exists. The problem with this is that it doesn't return information on who owns the lock. Now it always returns 1 instead of the proper process ID because of that.

• Could we check lock metadata instead of lock/release to check if a lock exists?
• We could add another column to the mysql.advisory_locks table to record the owner. However as the transaction never gets commited it would be difficult to get the record from other sessions/nodes.

[dveeden]

/test all

[dveeden]

The evalInt() now does a int64() on the owner pid before returning it. So sessions with an ID above MaxInt64 would likely have issues. Not sure how to properly return higher values.

[mjonss]

Maybe also add IS_FREE_LOCK() as an inverse of IS_USED_LOCK()?

[dveeden]

Maybe also add IS_FREE_LOCK() as an inverse of IS_USED_LOCK()?

Done in edb9729

MySQL

sql> select is_free_lock('test');
+----------------------+
| is_free_lock('test') |
+----------------------+
|                    1 |
+----------------------+
1 row in set (0.0004 sec)

sql> select get_lock('test',1);
+--------------------+
| get_lock('test',1) |
+--------------------+
|                  1 |
+--------------------+
1 row in set (0.0007 sec)

sql> select is_free_lock('test');
+----------------------+
| is_free_lock('test') |
+----------------------+
|                    0 |
+----------------------+
1 row in set (0.0064 sec)

sql> select version();
+-----------+
| version() |
+-----------+
| 8.0.33    |
+-----------+
1 row in set (0.0007 sec)

TiDB

+----------------------+
| is_free_lock('test') |
+----------------------+
|                    1 |
+----------------------+
1 row in set (0.0042 sec)

sql> select get_lock('test',1);
+--------------------+
| get_lock('test',1) |
+--------------------+
|                  1 |
+--------------------+
1 row in set (0.0026 sec)

sql> select is_free_lock('test');
+----------------------+
| is_free_lock('test') |
+----------------------+
|                    0 |
+----------------------+
1 row in set (0.0010 sec)

[dveeden]

/test all

[dveeden]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mjonss, tiancaiamao

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• OWNERS [mjonss,tiancaiamao]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-06-08 14:02:10.099037304 +0000 UTC m=+6944.346959128: ☑️ agreed by mjonss.
• 2023-06-21 02:04:12.180955518 +0000 UTC m=+154817.582205967: ☑️ agreed by tiancaiamao.

[tiancaiamao]

/merge