As of MySQL Version 3.23.6, you can choose between three basic
table formats (ISAM, HEAP and MyISAM). Newer
versions of MySQL support additional table types (InnoDB,
or BDB), depending on how you compile it. A database may contain
tables of different types.
When you create a new table, you can tell MySQL what type of table to create.
The default table type is usually MyISAM.
MySQL will always create a .frm file to hold the table and column
definitions. The table's index and data will be stored in one or more other
files, depending on the table type.
If you try to use a table type that is not compiled-in or activated,
MySQL will instead create a table of type MyISAM. This behavior
is convenient when you want to copy tables between MySQL servers that
support different table types. (Perhaps your master server supports
transactional storage engines for increased safety, while the slave servers use
only non-transactional storage engines for greater speed.)
This automatic change of table types can be confusing for new MySQL users. We
plan to fix this by introducing warnings in the new client/server protocol in
version 4.1 and generating a warning when a table type is automatically changed.
You can convert tables between different types with the ALTER TABLE statement. See ALTER TABLE.
Note that MySQL supports two different kinds of
tables: transaction-safe tables (InnoDB and BDB)
and not transaction-safe tables (HEAP, ISAM,
MERGE, and MyISAM).
Advantages of transaction-safe tables (TST):
Safer. Even if MySQL crashes or you get hardware problems, you
can get your data back, either by automatic recovery or from a backup
+ the transaction log.
You can combine many statements and accept these all in one go with
the COMMIT command.
You can execute ROLLBACK to ignore your changes (if you are not
running in auto-commit mode).
If an update fails, all your changes will be restored. (With NTST tables all
changes that have taken place are permanent)
Can provide better concurrency if the table gets many updates concurrently
with reads.
Note that to use InnoDB tables you have to use at least the
innodb_data_file_path startup option. See InnoDB start.
Advantages of not transaction-safe tables (NTST):
Much faster as there is no transaction overhead.
Will use less disk space as there is no overhead of transactions.
Will use less memory to do updates.
You can combine TST and NTST tables in the same statements to get the best
of both worlds.