On Mon, Jun 22, 2009 at 4:41 PM, Little,
> We have a 20 gig db (that includes the MYIs and MYDs and FRMs).
> We are wondering how long LVM snapshots take.. in that how long might
> the DB be read-locked? Do we have to read-lock it and flush tables?
> Are we talking half a second, ten-seconds, 20 minutes?
It depends. Long-running queries will block FLUSH TABLES WITH READ
LOCK, if you're using it, which will in turn block other queries. So
FLUSH TABLES WITH READ LOCK itself can take a long time. If you're
using only InnoDB tables you don't need to do that, you can just take
the snapshot and go. Upon recovery on the other server you can find
the binlog position in InnoDB's messages to the error log.
There are a lot of subtleties to all of this, so maybe you can give a
few more details about your setup.