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. MyISAM
table indexes
can always be reconstructed based on the data rows.
Fixed-length row format is available only for tables having no
BLOB
or
TEXT
columns. Creating a table
having such columns with an explicit
ROW_FORMAT
clause does not raise an error
or warning; the format specification is ignored.
Static-format tables have these characteristics:
CHAR
andVARCHAR
columns are space-padded to the specified column width, although the column type is not altered.BINARY
andVARBINARY
columns are padded with0x00
bytes to the column width.NULL
columns require additional space in the row to record whether their values areNULL
. EachNULL
column takes one bit extra, rounded up to the nearest byte.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.
The expected row length in bytes for static-sized rows is calculated using the following expression:
row length = 1 + (sum of column lengths) + (number of NULL columns + delete_flag + 7)/8 + (number of variable-length columns)
delete_flag
is 1 for tables with static row format. Static tables use a bit in the row record for a flag that indicates whether the row has been deleted.delete_flag
is 0 for dynamic tables because the flag is stored in the dynamic row header.