MDEV-25236 Online log apply fails for ROW_FORMAT=REDUNDANT tables
In other ROW_FORMAT than REDUNDANT, the InnoDB record header
size calculation depends on dict_index_t::n_core_null_bytes.
In ROW_FORMAT=REDUNDANT, the record header always is 6 bytes
plus n_fields or 2*n_fields bytes, depending on the maximum
record size. But, during online ALTER TABLE, the log records
in the temporary file always use a format similar to
ROW_FORMAT=DYNAMIC, even omitting the 5-byte fixed-length part
of the header.
While creating a temporary file record for a ROW_FORMAT=REDUNDANT
table, InnoDB must refer to dict_index_t::n_nullable.
The field dict_index_t::n_core_null_bytes is only valid for
other than ROW_FORMAT=REDUNDANT tables.
The bug does not affect MariaDB 10.3, because only
commit 7a27db778e3e5a04271568a94c75157bb6fb48f1 (MDEV-15563)
allowed an ALGORITHM=INSTANT change of a NOT NULL column to
NULL in a ROW_FORMAT=REDUNDANT table.
The fix was developed by Thirunarayanan Balathandayuthapani
and tested by Matthias Leich. The test case was simplified by me.
MDEV-26077 Assertion err != DB_DUPLICATE_KEY or unexpected ER_TABLE_EXISTS_ERROR
This is a backport of 161e4bfafd261aa5204827086637d4d7dcceb949.
trans_rollback_to_savepoint(): Only release metadata locks (MDL)
if the storage engines agree, after the changes were already rolled back.
Ever since commit 3792693f311a90cf195ec6d2f9b3762255a249c7
and mysql/mysql-server@55ceedbc3feb911505dcba6cee8080d55ce86dda
we used to cheat here and always release MDL if the binlog is disabled.
MDL are supposed to prevent race conditions between DML and DDL also
when no replication is in use. MDL are supposed to be a superset of
InnoDB table locks: InnoDB table lock may only exist if the thread
also holds MDL on the table name.
In the included test case, ROLLBACK TO SAVEPOINT would wrongly release
the MDL on both tables and let ALTER TABLE proceed, even though the DML
transaction is actually holding locks on the table.
Until commit 1bd681c8b3c5213ce1f7976940a7dc38b48a0d39 (MDEV-25506)
in MariaDB 10.6, InnoDB would often work around the locking violation
in a blatantly non-ACID way: If locks exist on a table that is being
dropped (in this case, actually a partition of a table that is being
rebuilt by ALTER TABLE), InnoDB could move the table (or partition)
into a queue, to be dropped after the locks and references had been
released. If the lock is not released and the original copy of the
table not dropped quickly enough, a name conflict could occur on
a subsequent ALTER TABLE.
The scenario of commit 3792693f311a90cf195ec6d2f9b3762255a249c7
is unaffected by this fix, because mysqldump
would use non-locking reads, and the transaction would not be holding
any InnoDB locks during the execution of ROLLBACK TO SAVEPOINT.
MVCC reads inside InnoDB are only covered by MDL and page latches,
not by any table or record locks.
FIXME: It would be nice if storage engines were specifically asked
which MDL can be released, instead of only offering a choice
between all or nothing. InnoDB should be able to release any
locks for tables that are no longer in trx_t::mod_tables, except
if another transaction had converted some implicit record locks
to explicit ones, before the ROLLBACK TO SAVEPOINT had been completed.
Reviewed by: Sergei Golubchik
