(Fixing both InnoDB and XtraDB)
Re-opening a TABLE object (after e.g. FLUSH TABLES or open table cache
eviction) causes ha_innobase to call
dict_stats_update(DICT_STATS_FETCH_ONLY_IF_NOT_IN_MEMORY).
Inside this call, the following is done:
dict_stats_empty_table(table);
dict_stats_copy(table, t);
On the other hand, commands like UPDATE make this call to get the "rows in
table" statistics in table->stats.records:
ha_innobase->info(HA_STATUS_VARIABLE|HA_STATUS_NO_LOCK)
note the HA_STATUS_NO_LOCK parameter. It means, no locks are taken by
::info() If the ::info() call happens between dict_stats_empty_table
and dict_stats_copy calls, the UPDATE's optimizer will get an estimate
of table->stats.records=1, which causes it to pick a full table scan,
which in turn will take a lot of row locks and cause other bad
consequences.
commit ef92aaf9ec
Author: Jan Lindström <jan.lindstrom@mariadb.com>
Date: Wed Jun 22 22:37:28 2016 +0300
MDEV-10083: Orphan ibd file when playing with foreign keys
Analysis: row_drop_table_for_mysql did not allow dropping
referenced table even in case when actual creating of the
referenced table was not successfull if foreign_key_checks=1.
Fix: Allow dropping referenced table even if foreign_key_checks=1
if actual table create returned error.
while according to Storage Engine API column names should be compared
case insensitively. This can cause FRM and InnoDB data dictionary to
go out of sync.
There is several different ways to incorrectly define
foreign key constraint. In many cases earlier MariaDB
versions the error messages produced by these cases
are not very clear and helpful. This patch improves
the warning messages produced by foreign key parsing.
Analysis: MySQL table definition contains also virtual columns. Similarly,
index fielnr references MySQL table fields. However, InnoDB table definition
does not contain virtual columns. Therefore, when matching MySQL key fieldnr
we need to use actual column name to find out referenced InnoDB dictionary
column name.
Fix: Add new function to match MySQL index key columns to InnoDB dictionary.
