Rollback Syntax; Storage Engine; 14.1. The Myisam - Oracle 5.0 Reference Manual

• They are safer. Even if MySQL crashes or you get hardware problems, you can get your data back,
either by automatic recovery or from a backup plus the transaction log.
• You can combine many statements and accept them all at the same time with the
(if autocommit is disabled).
• You can execute
• If an update fails, all of your changes are reverted. (With nontransaction-safe tables, all changes that
have taken place are permanent.)
• Transaction-safe storage engines can provide better concurrency for tables that get many updates
concurrently with reads.
You can combine transaction-safe and nontransaction-safe tables in the same statements to get the
best of both worlds. However, although MySQL supports several transaction-safe storage engines,
for best results, you should not mix different storage engines within a transaction with autocommit
disabled. For example, if you do this, changes to nontransaction-safe tables still are committed
immediately and cannot be rolled back. For information about this and other problems that can occur
in transactions that use mixed storage engines, see
and
ROLLBACK
Nontransaction-safe tables have several advantages of their own, all of which occur because there is
no transaction overhead:
• Much faster
• Lower disk space requirements
• Less memory required to perform updates
14.1. The
MyISAM
is the default storage engine. It is based on the older (and no longer available)
MyISAM
engine but has many useful extensions.
Each
MyISAM
and have an extension to indicate the file type. An
an (MYData) extension. The index file has an
.MYD
To specify explicitly that you want a
CREATE TABLE t (i INT) ENGINE = MYISAM;
The older term
the preferred term and
Normally, it is unnecessary to use
default engine unless the default has been changed. To ensure that
where the default might have been changed, include the
You can check or repair
also compress
"mysqlcheck
Maintenance
Tables".
tables have the following characteristics:
MyISAM
• All data values are stored with the low byte first. This makes the data machine and operating
system independent. The only requirements for binary portability are that the machine uses two's-
complement signed integers and IEEE floating-point format. These requirements are widely used
among mainstream machines. Binary compatibility might not be applicable to embedded systems,
which sometimes have peculiar processors.
The
to ignore your changes (if autocommit is disabled).
ROLLBACK
Syntax".

Storage Engine

table is stored on disk in three files. The files have names that begin with the table name
is supported as a synonym for
TYPE
is deprecated.
TYPE
ENGINE
tables with the
MyISAM
tables with
MyISAM myisampack
— A Table Maintenance
Utility", and Section 4.6.5,
Storage Engine
MyISAM
Section 13.3.1,
file stores the table format. The data file has
.frm
(MYIndex) extension.
.MYI
table, indicate that with an
MyISAM
ENGINE
to specify the
MyISAM
ENGINE
mysqlcheck
to take up much less space. See
Program", Section 4.6.3,
"myisampack — Generate Compressed, Read-Only MyISAM
1218
"START
TRANSACTION, COMMIT,
table option:
ENGINE
for backward compatibility, but
storage engine.
MyISAM
is used in situations
MyISAM
option explicitly.
client or
myisamchk
Section 4.5.3,
"myisamchk — MyISAM Table-
statement
COMMIT
storage
ISAM
is
ENGINE
is the
utility. You can