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5.4.6 The DDL Log
The DDL log, or metadata log, records metadata operations
generated by data definition statements such as
DROP TABLE and
ALTER TABLE. MySQL uses this log to
recover from crashes occurring in the middle of a metadata
operation. When executing the statement DROP TABLE t1,
t2, we need to ensure that both t1
and t2 are dropped, and that each table drop is
complete. Another example of this type of SQL statement is
ALTER
TABLE t3 DROP PARTITION p2, where we must make certain
that the partition is completely dropped and that its definition
is removed from the list of partitions for table
t3.
A record of metadata operations such as those just described are
written to the file ddl_log.log, in the MySQL
data directory. This is a binary file; it is not intended to be
human-readable, and you should not attempt to modify its contents
in any way.
ddl_log.log is not created until it is
actually needed for recording metadata statements, and is removed
following a successful start of mysqld. Thus,
it is possible for this file not to be present on a MySQL server
that is functioning in a completely normal manner.
Currently, ddl_log.log can hold up to 1048573
entries, equivalent to 4 GB in size. Once this limit is exceeded,
you must rename or remove the file before it is possible to
execute any additional DDL statements. This is a known issue which
we are working to resolve (Bug #83708).
There are no user-configurable server options or variables associated with this file.
Document created the 26/06/2006, last modified the 26/10/2018
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