(mysql.info.gz) ISAM storage engine

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 14.9 The `ISAM' Storage Engine
 ==============================
 
 The original storage engine in MySQL was the `ISAM' engine. It was the
 only storage engine available until MySQL 3.23, when the improved
 `MyISAM' engine was introduced as the default. `ISAM' is deprecated.
 As of MySQL 4.1, it's included in the source but not enabled in binary
 distributions.  It is not available in MySQL 5.0.  Embedded MySQL
 server versions do not support `ISAM' tables by default.
 
 Due to the deprecated status of `ISAM', and because `MyISAM' is an
 improvement over `ISAM', you are advised to convert any remaining
 `ISAM' tables to `MyISAM' as soon as possible.  To convert an `ISAM'
 table to a `MyISAM' table, use an `ALTER TABLE' statement:
 
      mysql> ALTER TABLE TBL_NAME TYPE = MYISAM;
 
 For more information about `MyISAM', see  `MyISAM' storage engine
 MyISAM storage engine.
 
 Each `ISAM' table is stored on disk in three files.  The files have
 names that begin with the table name and have an extension to indicate
 the file type.  An `.frm' file stores the table definition.  The data
 file has an `.ISD' extension.  The index file has an `.ISM' extension.
 
 `ISAM' uses B-tree indexes.
 
 You can check or repair `ISAM' tables with the `isamchk' utility.
  Crash recovery.
 
 `ISAM' has the following properties:
 
    * Compressed and fixed-length keys
 
    * Fixed and dynamic record length
 
    * 16 indexes per table, with 16 key parts per key
 
    * Maximum key length 256 bytes (default)
 
    * Data values are stored in machine format; this is fast, but
      machine/OS dependent
 
 Many of the properties of `MyISAM' tables are also true for `ISAM'
 tables. However, there are also many differences. The following list
 describes some of the ways that `ISAM' is distinct from `MyISAM':
 
    * Not binary portable across OS/platforms.
 
    * Can't handle tables larger than 4GB.
 
    * Only supports prefix compression on strings.
 
    * Smaller (more restrictive) key limits.
 
    * Dynamic tables become more fragmented.
 
    * Doesn't support `MERGE' tables.
 
    * Tables are checked and repaired with `isamchk' rather than with
      `myisamchk'.
 
    * Tables are compressed with `pack_isam' rather than with
      `myisampack'.
 
    * Cannot be used with the `BACKUP TABLE' or  `RESTORE TABLE'
      backup-related statements.
 
    * Cannot be used with the `CHECK TABLE', `REPAIR TABLE', `OPTIMIZE
      TABLE', or `ANALYZE TABLE' table-maintenance statements.
 
    * No support for full-text searching or spatial data types.
 
    * No support for multiple character sets per table.
 
    * Indexes cannot be assigned to specific key caches.
 
 

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