• Recorddata 

How many bytes in the data file are used. 

• Deleted data 

How many bytes in the data file are deleted (unused). 

• Lost space 

If a row is updated to a shorter length, some space is lost. This is the sum of all such losses, in bytes. 

• Linkdata 

When the dynamic table format is used, row fragments are linked with pointers (4 to 7 bytes each). Linkdata  is the sum of the amount of storage used by all such pointers. 

## 4.6.4.6 myisamchk Memory Usage 

Memory allocation is important when you run myisamchk . myisamchk  uses no more memory than its memory-related variables are set to. If you are going to use myisamchk  on very large tables, you should first decide how much memory you want it to use. The default is to use only about 3MB to perform repairs. By using larger values, you can get myisamchk  to operate faster. For example, if you have more than 512MB RAM available, you could use options such as these (in addition to any other options you might specify): 

myisamchk --myisam_sort_buffer_size=256M \ --key_buffer_size=512M \ --read_buffer_size=64M \ --write_buffer_size=64M ... 

Using --myisam_sort_buffer_size=16M  is probably enough for most cases. 

Be aware that myisamchk  uses temporary files in TMPDIR . If TMPDIR  points to a memory file system, out of memory errors can easily occur. If this happens, run myisamchk  with the --tmpdir= dir_name  option to specify a directory located on a file system that has more space. 

When performing repair operations, myisamchk  also needs a lot of disk space: 

•Twice the size of the data file (the original file and a copy). This space is not needed if you do a repair with --quick ; in this case, only the index file is re-created. This space must be available on the same file system as the original data file , as the copy is created in the same directory as the original. 

•Space for the new index file that replaces the old one. The old index file is truncated at the start of the repair operation, so you usually ignore this space. This space must be available on the same file system as the original data file. 

•When using --recover  or --sort-recover  (but not when using --safe-recover ), you need space on disk for sorting. This space is allocated in the temporary directory (specified by TMPDIR  or -- tmpdir= dir_name ). The following formula yields the amount of space required: 

( largest_key  + row_pointer_length ) * number_of_rows  * 2 

You can check the length of the keys and the row_pointer_length  with myisamchk - dv tbl_name  (see Section 4.6.4.5, “Obtaining Table Information with myisamchk” ). The row_pointer_length  and number_of_rows  values are the Datafile pointer  and Data records  values in the table description. To determine the largest_key  value, check the Key  lines in 

