fix: Use prefilter for delete with subquery

[juliusknorr]

It seems that MySQL is badly optimizing DELETE FROM .. WHERE IN with subqueries as in that a full table scan and row locks are done when the subquery returns no result. In most cases we have a document id so we can apply it to the delete query itself to reduce the amount of rows to scan.

Before

MariaDB [oc]> EXPLAIN DELETE FROM `oc_text_sessions` WHERE `id` IN (SELECT `s`.`id` FROM `oc_text_sessions` `s` LEFT JOIN `oc_text_steps` `st` ON `st`.`session_id` = `s`.`id` WHERE (`last_contact` < '1689576710') AND (`st`.`id` IS NULL)
AND (`s`.`document_id` = '7197220'));
+------+--------------------+------------------+-------+---------------------------------------------+----------------------+---------+---------+------+--------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+--------------------+------------------+-------+---------------------------------------------+----------------------+---------+---------+------+--------------------------------------+
| 1 | PRIMARY | oc_text_sessions | ALL | NULL | NULL | NULL | NULL | 1364 | Using where |
| 2 | DEPENDENT SUBQUERY | s | range | PRIMARY,ts_docid_lastcontact,ts_lastcontact | ts_docid_lastcontact | 16 | NULL | 1 | Using where; Using index |
| 2 | DEPENDENT SUBQUERY | st | ref | ts_session | ts_session | 8 | oc.s.id | 3 | Using where; Using index; Not exists |
+------+--------------------+------------------+-------+---------------------------------------------+----------------------+---------+---------+------+--------------------------------------+

After

MariaDB [oc]> EXPLAIN DELETE FROM `oc_text_sessions` WHERE document_id = '7197220' AND `id` IN (SELECT `s`.`id` FROM `oc_text_sessions` `s` LEFT JOIN `oc_text_steps` `st` ON `st`.`session_id` = `s`.`id` WHERE (`last_contact` < '168957671
0') AND (`st`.`id` IS NULL)
+------+--------------------+------------------+-------+---------------------------------------------+----------------------+---------+---------+------+--------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+--------------------+------------------+-------+---------------------------------------------+----------------------+---------+---------+------+--------------------------------------+
| 1 | PRIMARY | oc_text_sessions | range | ts_docid_lastcontact | ts_docid_lastcontact | 8 | NULL | 4 | Using where |
| 2 | DEPENDENT SUBQUERY | s | range | PRIMARY,ts_docid_lastcontact,ts_lastcontact | ts_docid_lastcontact | 16 | NULL | 1 | Using where; Using index |
| 2 | DEPENDENT SUBQUERY | st | ref | ts_session | ts_session | 8 | oc.s.id | 3 | Using where; Using index; Not exists |
+------+--------------------+------------------+-------+---------------------------------------------+----------------------+---------+---------+------+--------------------------------------+

[cypress]

1 flaky tests on run #11137 ↗︎

0

149

2

0

1

Details:

fix: Use prefilter for delete with subquery
Project: Text	Commit:5e9259812a
Status: Passed	Duration: 03:38 💡
Started: Jul 17, 2023 7:42 AM	Ended: Jul 17, 2023 7:45 AM

cypress/e2e/nodes/HardBreak.spec.js • 1 flaky test

ViewOutputVideo

Test		Artifacts
Hard break support > Can create hard breaks with shift+enter		OutputScreenshots

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[juliusknorr]

Let me cherry pick this to the existing backports of #4521