what does myisam mean

Myisam is the default storage engine before mysql5.1. It is based on older ISAM code, but has many useful extensions. Each MyISAM is stored as three files on disk. The name of each file starts with the name of the table and the extension indicates the file type.

myisam introduction

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MyISAM is the default storage engine (Before Mysql5.1 version). It is based on older ISAM code, but has many useful extensions. (Note that MySQL 5.1 does not support ISAM). Each MyISAM is stored as three files on disk. The name of each file starts with the name of the table, and the extension indicates the file type.

Detailed introduction

To explicitly indicate that you want to use a MyISAM table, please indicate it using the ENGINE table option:

CREATE TABLE t (i INT) ENGINE = MYISAM;

Note: Older versions of MySQL use TYPE instead ENGINE (for example, TYPE = MYISAM). MySQL 5.1 supports this syntax for backward compatibility, but TYPE is now deprecated, and ENGINE is the first usage.

Generally, the ENGINE option is unnecessary; unless the default has been changed, InnoDB is the default storage engine (after Mysql 5.1).

Some features of MyISAM storage engine

1. All data values ​​are stored in the low byte first.

This separates the data machine and operating system. The only requirements for binary portability are that the machine uses two's complement (as machines of the last 20 years have) and the IEEE floating point format (which is also completely dominant in mainstream machines). The only machines that don't support binary compatibility are embedded systems. These systems sometimes use special processors.

Storing the low bytes of data first does not seriously affect speed; bytes in data rows are generally unjoined, and reading unjoined bytes in one direction does not take more time than reading in the reverse direction. H. The code on the server that gets the column value is not as time-critical as other code.

2. Large files (up to 63-bit file length) are supported on file systems and operating systems that support large files.

3. Dynamically sized rows are less fragmented when deletions are mixed with updates and inserts. This is done automatically by merging adjacent deleted blocks and extending to the next block if it is deleted.

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