Comments on: How alter table locks tables and handles transactions http://ebergen.net/wordpress/2007/05/07/how-alter-table-locks-tables-and-handles-transactions/ You will probably want some waders, a pick axe, and one of those hats with a light on it before you go in here. Wed, 20 Aug 2008 07:35:17 +0000 http://wordpress.org/?v=2.5.1 By: Lukas http://ebergen.net/wordpress/2007/05/07/how-alter-table-locks-tables-and-handles-transactions/#comment-32827 Lukas Mon, 11 Jun 2007 14:43:10 +0000 http://ebergen.net/wordpress/2007/05/07/how-alter-table-locks-tables-and-handles-transactions/#comment-32827 a LOCK TABLE call is another alternative, but if you have users that have to wait then, its probably best to take the server down, especially if you have other servers that can take over .. a LOCK TABLE call is another alternative, but if you have users that have to wait then, its probably best to take the server down, especially if you have other servers that can take over ..

]]> By: Pythian Group Blog » Log Buffer #44: a Carnival of the Vanities for DBAs http://ebergen.net/wordpress/2007/05/07/how-alter-table-locks-tables-and-handles-transactions/#comment-25536 Pythian Group Blog » Log Buffer #44: a Carnival of the Vanities for DBAs Fri, 11 May 2007 16:54:00 +0000 http://ebergen.net/wordpress/2007/05/07/how-alter-table-locks-tables-and-handles-transactions/#comment-25536 [...] table during alter table and other times they can’t. Also why it’s so slow.” He explains how alter table locks tables and handles transactions with a little help from Heikki [...] [...] table during alter table and other times they can’t. Also why it’s so slow.” He explains how alter table locks tables and handles transactions with a little help from Heikki [...]

]]> By: Heikki Tuuri http://ebergen.net/wordpress/2007/05/07/how-alter-table-locks-tables-and-handles-transactions/#comment-24813 Heikki Tuuri Tue, 08 May 2007 05:32:41 +0000 http://ebergen.net/wordpress/2007/05/07/how-alter-table-locks-tables-and-handles-transactions/#comment-24813 Eric, actually, the right solution would be to return from the SELECT an error like "snapshot too old", at least in the second SELECT above. We should compare the table timestamp to the consistent read snapshot timestamp. Please file an InnoDB bug report to bugs.mysql.com about this. Regards, Heikki Eric,

actually, the right solution would be to return from the SELECT an error like “snapshot too old”, at least in the second SELECT above.

We should compare the table timestamp to the consistent read snapshot timestamp.

Please file an InnoDB bug report to bugs.mysql.com about this.

Regards,

Heikki

]]> By: Heikki Tuuri http://ebergen.net/wordpress/2007/05/07/how-alter-table-locks-tables-and-handles-transactions/#comment-24812 Heikki Tuuri Tue, 08 May 2007 05:29:08 +0000 http://ebergen.net/wordpress/2007/05/07/how-alter-table-locks-tables-and-handles-transactions/#comment-24812 Eric, InnoDB, in an ALTER TABLE, commits the row-copying transaction at every 10,000 copied rows. That is to save space in the undo log. What I do not understand is why you in the second result above only get 5 rows back. How big was the table that you ALTERed? Since an ALTER destroys the history information for rows, there is no way InnoDB's consistent read could work in a consistent way over an ALTER TABLE. I hope this is mentioned in the MySQL manual. "I’m not sure why innodb allows rename of a table when transactions still have a few of that table open. It seems like a bug to me." We really cannot block ALTER or RENAME whenever someone has a consistent read snapshot open anywhere in the database. It would cause too long waits. Regards, Heikki Eric,

InnoDB, in an ALTER TABLE, commits the row-copying transaction at every 10,000 copied rows. That is to save space in the undo log.

What I do not understand is why you in the second result above only get 5 rows back. How big was the table that you ALTERed?

Since an ALTER destroys the history information for rows, there is no way InnoDB’s consistent read could work in a consistent way over an ALTER TABLE. I hope this is mentioned in the MySQL manual.

“I’m not sure why innodb allows rename of a table when transactions still have a few of that table open. It seems like a bug to me.”

We really cannot block ALTER or RENAME whenever someone has a consistent read snapshot open anywhere in the database. It would cause too long waits.

Regards,

Heikki

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