Auto-create of SYSTEM_TIME history partitions checks the partition limit without existing partitions and subpartitions

partition_info::vers_set_hist_part() (sql/partition_info.cc) counts the history partitions to auto-create for INTERVAL ... AUTO and stops with

if (*create_count == MAX_PARTITIONS - 2)

{

  my_error(ER_TOO_MANY_PARTITIONS_ERROR, MYF(ME_WARNING));

  my_error(ER_VERS_HIST_PART_FAILED, ...);

  return true;

}

The limit compares only the number of new partitions with MAX_PARTITIONS - 2. It ignores the partitions the table already has and the number of subpartitions, so the real total ((num_parts + create_count) * num_subparts) can be well over MAX_PARTITIONS while this check passes. The early error is then not given, and the limit is left to whatever checks the actual partition creation does.

MDEV-25529 adds vers_calc_hist_parts(), which sizes the layout at ALTER time with the correct limit ((n + 1) * num_subparts > MAX_PARTITIONS). The two should use one shared counting helper so that sizing at ALTER and auto-creation at DML agree.

Present in 10.11 and later (auto-create since 10.9).

Found during review of MDEV-25529 (https://github.com/MariaDB/server/pull/5294); the code predates that change.