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13.1.3.2 Dynamic Table Characteristics »
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13.1.3.1. Static (Fixed-Length) Table Characteristics

Static format is the default for MyISAM tables. It is used when the table contains no variable-length columns (VARCHAR, VARBINARY, BLOB, or TEXT). Each row is stored using a fixed number of bytes.

Of the three MyISAM storage formats, static format is the simplest and most secure (least subject to corruption). It is also the fastest of the on-disk formats due to the ease with which rows in the data file can be found on disk: To look up a row based on a row number in the index, multiply the row number by the row length to calculate the row position. Also, when scanning a table, it is very easy to read a constant number of rows with each disk read operation.

The security is evidenced if your computer crashes while the MySQL server is writing to a fixed-format MyISAM file. In this case, myisamchk can easily determine where each row starts and ends, so it can usually reclaim all rows except the partially written one. Note that MyISAM table indexes can always be reconstructed based on the data rows.

Note

Fixed-length row format is only available for tables without BLOB or TEXT columns. Creating a table with these columns with an explicit ROW_FORMAT clause will not raise an error or warning; the format specification will be ignored.

Static-format tables have these characteristics:

  • CHAR and VARCHAR columns are space-padded to the specified column width, although the column type is not altered. This is also true for NUMERIC and DECIMAL columns created before MySQL 5.0.3. BINARY and VARBINARY columns are space-padded to the column width before MySQL 5.0.15. As of 5.0.15, BINARY and VARBINARY columns are padded with 0x00 bytes.

  • Very quick.

  • Easy to cache.

  • Easy to reconstruct after a crash, because rows are located in fixed positions.

  • Reorganization is unnecessary unless you delete a huge number of rows and want to return free disk space to the operating system. To do this, use OPTIMIZE TABLE or myisamchk -r.

  • Usually require more disk space than dynamic-format tables.


User Comments

Posted by Ganesh Prabhu on May 27 2004 1:59pm[Delete] [Edit]

Storage space used by NULL columns:

If the table is Fixed-length the NULL coumns take up same space as they would have taken if they contained a value.

If there are lot of NULL columns and you want to save some space, then ALTER the table by adding a variable length column. That will make the table storage type as 'Dynamic' and the NULL coulmns will take up only one bit/byte.

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