MDEV-38822 Lock wait timeout during CREATE TABLE AS SELECT FROM mysql.innodb_table_stats

[Thirunarayanan]

Analysis:

1. Starts the CREATE TABLE ... SELECT and acquires an Intent Shared lock on mysql.innodb_table_stats to read the rows. (Transaction: T1)

2. The table t1 is populated. As part of the post-copy phase (introduced by MDEV-35163), InnoDB triggers the statistics update.

3. InnoDB opens a new internal transaction to update the statistics. This transaction(T2) attempts to acquire an LOCK_X on the same table in mysql.innodb_table_stats. T2 (x-lock) must wait for T1 to commit or rollback because X-locks are incompatible with IS locks from other trasnaction.

Solution:

Currently, Intermediate tables don't trigger dict_stats_update_if_needed(), so they require explicit stats update via alter_stats_rebuild(). For CREATE...SELECT stats are updated automatically through the normal DML path via dict_stats_update_if_needed()

Skip calling dict_stats_update() in alter_stats_rebuild() for non-intermediate tables when using copy algorithm, since their statistics will be updated automatically via dict_stats_update_if_needed().

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