Re: myisam_sort_buffer_size

[Rick James]

The documentation is sketchy:

Quote

The size of the buffer that is allocated when sorting MyISAM indexes during a REPAIR TABLE or when creating indexes with CREATE INDEX or ALTER TABLE.

The maximum allowable setting for myisam_sort_buffer_size is 4GB. As of MySQL 5.1.23, values larger than 4GB are allowed for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB with a warning).

-- http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html#sysvar_myisam_sort_buffer_size

I think it is used for ALTER, REPAIR, OPTIMIZE, and LOAD DATA; set it when you need it. It is probably per-thread, so don't set it to a high value until you need it. See comment 3 in http://www.mysqlperformanceblog.com/2006/05/17/mysql-server-memory-usage/