Commits on May 14, 2024

1. MDEV-32397, MDEV-32403 Crashes during join processing. …

   Queries having the following form may cause a crash
     SELECT t1.a FROM ( SELECT a AS a1 FROM t1 ) dt
     JOIN t1 ON a1 LIKE EXISTS ( SELECT a + RAND () FROM t1 UNION SELECT a FROM t1);
   because the table t1 has some JOIN cleanup operations performed prematurely
   during the subselect.
   
   In this particular case, the presence of RAND() makes the subquery
   uncacheable, necessitating the need to execute the subquery multiple
   times during join record evaluation.  Each time the subquery runs, it
   creates its own JOIN structure which has references to the table t1.
   When the subquery completes, JOIN::cleanup and functions called by it
   result in ha_end_keyread() being called on table t1.  However, we are
   not done with table t1 because the upper level `select t1.a from...`
   query requires table t1 to be open.  To solve this, we make the executor
   aware of when we're in subqueries like this and delay JOIN cleanup
   until the end of the query.

   

   DaveGosselin-MariaDB committed May 14, 2024
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