MySQL 8.0 Release Notes
MySQL 8.0 Source Code Documentation
To coalesce fragmented rows and eliminate wasted space that results from deleting or updating rows, run myisamchk in recovery mode:
shell> myisamchk -r tbl_name
You can optimize a table in the same way by using the
OPTIMIZE TABLE SQL statement.
OPTIMIZE TABLE does a table
repair and a key analysis, and also sorts the index tree so that
key lookups are faster. There is also no possibility of unwanted
interaction between a utility and the server, because the server
does all the work when you use OPTIMIZE
TABLE. See Section 13.7.3.4, “OPTIMIZE TABLE Syntax”.
myisamchk has a number of other options that you can use to improve the performance of a table:
--analyzeor-a: Perform key distribution analysis. This improves join performance by enabling the join optimizer to better choose the order in which to join the tables and which indexes it should use.--sort-indexor-S: Sort the index blocks. This optimizes seeks and makes table scans that use indexes faster.--sort-records=orindex_num-R: Sort data rows according to a given index. This makes your data much more localized and may speed up range-basedindex_numSELECTandORDER BYoperations that use this index.
For a full description of all available options, see Section 4.6.4, “myisamchk — MyISAM Table-Maintenance Utility”.