On Thursday, October 30, 2003, at 08:19 AM, Leonardo Rodrigues wrote:
My question are: are these commands similar to VACUUM? What´s the difference? How can I run on InnoDB?
I don't know much about PostgreSQL, so I'm not sure. If you describe what VACUUM does, I may be able to help explain how to do the same thing with MySQL.
Jeremy
I don't know if anyone else ever answered this, but VACUUM reclaims space in the PostgreSQL table data files. This is due to the Multi-Version Concurrency Control in PostgreSQL. Each record in a table is versioned, so, while in one transaction a user may be reading a record, say version 1, in another transaction, a user can be updating that record, which will then be version 2, and so on. Multiple copies of the record are kept (for rollback, etc.). VACUUM simply wipes out any old record versions that are no longer needed, reclaiming space in the data file.
This is not at all similar to ANALYZE TABLE, but more akin to OPTIMIZE TABLE in MySQL. According to the manual, this command only works on MyISAM and BDB.
- Gabriel
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