MDEV-32688 Add innodb_foreign_key_errors status variable

[y2kwak]

Description

Add a new status variable innodb_foreign_key_errors that tracks the total number of foreign key constraint violations in InnoDB, similar to innodb_deadlocks.

The counter increments for both child-side violations and parent-side violations. Counter resets to 0 on server restart.

Added test coverage in mysql-test/suite/innodb/t/foreign_key_errors.test.

How can this PR be tested?

Run the MTR test foreign_key_error.test

It can also be tested manually.

• Count starts at 0

MariaDB [(none)]> SHOW GLOBAL STATUS LIKE 'innodb_foreign_key_errors';
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| Innodb_foreign_key_errors | 0     |
+---------------------------+-------+
1 row in set (0.001 sec)

• Count increments after error

MariaDB [testdb]> INSERT INTO child VALUES (1, 999);
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`testdb`.`child`, CONSTRAINT `1` FOREIGN KEY (`parent_id`) REFERENCES `parent` (`id`))

MariaDB [testdb]> SHOW GLOBAL STATUS LIKE 'innodb_foreign_key_errors';
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| Innodb_foreign_key_errors | 1     |
+---------------------------+-------+
1 row in set (0.000 sec)

MariaDB [testdb]> UPDATE child SET parent_id = 999 WHERE id = 1;
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`testdb`.`child`, CONSTRAINT `1` FOREIGN KEY (`parent_id`) REFERENCES `parent` (`id`))

MariaDB [testdb]> SHOW GLOBAL STATUS LIKE 'innodb_foreign_key_errors';
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| Innodb_foreign_key_errors | 2     |
+---------------------------+-------+
1 row in set (0.000 sec)

Basing the PR against the correct MariaDB version

•  This is a new feature and the PR is based against the latest MariaDB development branch.

Copyright

All new code of the whole pull request, including one or several files that are either new files or modified ones, are contributed under the BSD-new license. I am contributing on behalf of my employer Amazon Web Services, Inc.

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[gkodinov]

to ensure that it indeed starts at 0, please make sure to either explicitly reset it (as mtr sometimes uses a running server instance that matches the start parameters for the current tests) or make sure that the test is always run on a freshly started server.

I'd do the former: saves one needless restart and lots of mtr run time.

This is why some of the build bot hosts are failing on your test btw.

[gkodinov]

say what the value needs to be please. makes it easier to read and check.

[gkodinov]

test reset too: FLUSH status.

[gkodinov]

Also, please, fix the commit message: do not mention the license in it. And remove the "similar to ..." part: it's not relevant.