GitLab

Fix for bug #46947 "Embedded SELECT without FOR UPDATE is
causing a lock", with after-review fixes.

SELECT statements with subqueries referencing InnoDB tables
were acquiring shared locks on rows in these tables when they
were executed in REPEATABLE-READ mode and with statement or
mixed mode binary logging turned on.

This was a regression which were introduced when fixing
bug 39843.

The problem was that for tables belonging to subqueries
parser set TL_READ_DEFAULT as a lock type. In cases when
statement/mixed binary logging at open_tables() time this
type of lock was converted to TL_READ_NO_INSERT lock at
open_tables() time and caused InnoDB engine to acquire
shared locks on reads from these tables. Although in some
cases such behavior was correct (e.g. for subqueries in
DELETE) in case of SELECT it has caused unnecessary locking.

This patch tries to solve this problem by rethinking our
approach to how we handle locking for SELECT and subqueries.
Now we always set ...