Comments on: Undo area size restriction needed for Innodb http://www.mysqlperformanceblog.com/2006/11/09/undo-area-size-restriction-needed-for-innodb/ Everything about MySQL Performance Sat, 21 Nov 2009 05:23:57 -0800 http://wordpress.org/?v=2.8.4 hourly 1 By: Pythian Group Blog » Log Buffer #18: a Carnival of the Vanities for DBAs http://www.mysqlperformanceblog.com/2006/11/09/undo-area-size-restriction-needed-for-innodb/comment-page-1/#comment-76278 Pythian Group Blog » Log Buffer #18: a Carnival of the Vanities for DBAs Fri, 09 Mar 2007 23:25:13 +0000 http://www.mysqlperformanceblog.com/2006/11/09/undo-tablespace-size-restriction-needed-for-innodb/#comment-76278 [...] Zaitsev of the MySQL Performance Blog has a similar story, Undo area size restriction needed for InnoDB. “…MySQL Server was restarted … and (spent) hours to undo almost 300.000.000 of [...] [...] Zaitsev of the MySQL Performance Blog has a similar story, Undo area size restriction needed for InnoDB. “…MySQL Server was restarted … and (spent) hours to undo almost 300.000.000 of [...]

]]> By: Xaprb http://www.mysqlperformanceblog.com/2006/11/09/undo-area-size-restriction-needed-for-innodb/comment-page-1/#comment-10641 Xaprb Fri, 17 Nov 2006 18:20:53 +0000 http://www.mysqlperformanceblog.com/2006/11/09/undo-tablespace-size-restriction-needed-for-innodb/#comment-10641 That's true. Another related thing I watch in innotop (this isn't directly relevant, but my "fuzzy logic" reminds me of it) is old versions kept around. You can do a little subtraction and see how many versions InnoDB is keeping in memory (snapshots created by selecting some rows in default isolation level). Until the transaction commits, InnoDB has to keep the old version in memory to present a consistent view to the transaction, so long-running transactions keep using memory. Like I said not completely relevant, but sort of related. (For those who want to use this feature, it is in the header in T mode -- press 'h' to show the header). That’s true. Another related thing I watch in innotop (this isn’t directly relevant, but my “fuzzy logic” reminds me of it) is old versions kept around. You can do a little subtraction and see how many versions InnoDB is keeping in memory (snapshots created by selecting some rows in default isolation level). Until the transaction commits, InnoDB has to keep the old version in memory to present a consistent view to the transaction, so long-running transactions keep using memory. Like I said not completely relevant, but sort of related.

(For those who want to use this feature, it is in the header in T mode — press ‘h’ to show the header).

]]> By: peter http://www.mysqlperformanceblog.com/2006/11/09/undo-area-size-restriction-needed-for-innodb/comment-page-1/#comment-9044 peter Wed, 15 Nov 2006 01:13:26 +0000 http://www.mysqlperformanceblog.com/2006/11/09/undo-tablespace-size-restriction-needed-for-innodb/#comment-9044 Xarb, This only shows undo space for active queries which would help in described case but may does not show it in all cases. Imagine for example transaction which is open for a week - it does not do changes itself so its undo entries number is zero. However it also does not allow Innodb to purge undo entries for transactions which have been committed in the meanwhile. Such transaction can affect performance a lot, however it does not affect recovery speed as such entries need to be purged rather than rolled back. Xarb,

This only shows undo space for active queries which would help in described case but may does not show it in all cases. Imagine for example transaction which is open for a week – it does not do changes itself so its undo entries number is zero. However it also does not allow Innodb to purge undo entries for transactions which have been committed in the meanwhile.

Such transaction can affect performance a lot, however it does not affect recovery speed as such entries need to be purged rather than rolled back.

]]> By: Xaprb http://www.mysqlperformanceblog.com/2006/11/09/undo-area-size-restriction-needed-for-innodb/comment-page-1/#comment-8807 Xaprb Tue, 14 Nov 2006 15:50:18 +0000 http://www.mysqlperformanceblog.com/2006/11/09/undo-tablespace-size-restriction-needed-for-innodb/#comment-8807 innotop (http://www.xaprb.com/innotop/) shows undo size in the InnoDB Transaction mode. Press capital T to enter this mode, and c to choose columns in case it is not already visible. This is also a good way to watch the progress of long queries; you can see how done the query is in case you know how many rows it should affect. I regularly watch transactions this way to see how long they are and how many undo log entries they generate. innotop (http://www.xaprb.com/innotop/) shows undo size in the InnoDB Transaction mode. Press capital T to enter this mode, and c to choose columns in case it is not already visible. This is also a good way to watch the progress of long queries; you can see how done the query is in case you know how many rows it should affect.

I regularly watch transactions this way to see how long they are and how many undo log entries they generate.

]]>