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  1. MariaDB Server
  2. MDEV-15072

Massive performance impact after PTI fix

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      Hello

      I have just applied the PTI patch on the OS and it is causing a massive difference in the execution time of a specific query.

      Disabling and reenabling PTI enables me to reproduce the difference at will :

      PTI disabled : 7s
      PTI enabled : 87s

      The query :

      SELECT * FROM `test` as b1 WHERE b1.`dateFin` > '2018-01-24' AND NOT EXISTS (SELECT 1 FROM `test` as b2 WHERE b2.`ip` = b1.`ip` AND b2.`dateFin` > b1.`dateFin`);
      

      Explain doesn't help much :

      +------+--------------------+-------+------+---------------+------+---------+------+------+-------------+
      | id   | select_type        | table | type | possible_keys | key  | key_len | ref  | rows | Extra       |
      +------+--------------------+-------+------+---------------+------+---------+------+------+-------------+
      |    1 | PRIMARY            | b1    | ALL  | NULL          | NULL | NULL    | NULL | 4499 | Using where |
      |    2 | DEPENDENT SUBQUERY | b2    | ALL  | NULL          | NULL | NULL    | NULL | 4499 | Using where |
      +------+--------------------+-------+------+---------------+------+---------+------+------+-------------+
      

      Can't see any report matching that kind of difference so far so i'm wondering what's up

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              Assignee:
              axel Axel Schwenke
              Reporter:
              falcoris Jean-Marc Messina
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