The Ultimate Guide to High Availability with MariaDB

Conversion of big IN predicates into subqueries

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Starting from MariaDB 10.3, the optimizer will convert big IN predicates into subqueries. That is, an IN predicate in form

column [NOT] IN (const1, const2, .... )

with a sufficiently large number of elements in the list (more than 1000) will be converted into a subquery:

column [NOT] IN (select ... from temporary_table)

Controlling the optimization

  • There is no optimizer_switch flag for this optimization.
  • Debug builds have @@in_predicate_conversion_threshold parameter.

https://jira.mariadb.org/browse/MDEV-12176

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