There are only a very limited set of circumstances where slaves could
get out of sync, and if everything is set up right, it basically should
not happen.
See: http://dev.mysql.com/doc/refman/5.0/en/replication-rules.html
And: http://dev.mysql.com/doc/refman/5.0/en/replication-features.html
CHECKSUM TABLE is a good option if it's a read-only table or you can
stop writes (or just replication) long enough to do that. It only works
on MyISAM.
You could also do basically the same thing by dumping the data in the
same way on each server, and running a checksum (e.g. md5sum) or diff
tool. One thing I have done is to use:
mysqldump --skip-opt {database} > {database}.sql
...on each machine, then diffed the files using "diff" (note *nix bias
here). Using skip-opt to output inserts on individual lines allows you
to compare the data to see exactly where any differences are. But this
won't help you if you can't transfer all the data to one place -- you
could just do a checksum then on both sides and compare that. Would be
pretty easy to script that and perform periodic checks.
Eric
--
Eric Braswell
Web Manager MySQL AB
Cupertino, USA
Robinson, Eric wrote:
I have master-slave replication working fine. However, I worry about the
possibility of the master and slave accidentally getting out of
synchronization. Are there circumstances (other than a direct INSERT to
the slave) that could cause the master and slave to be out of sync? Is
there a way to periodically do some kind of full check to verify that
the slave is an exact duplicate of the master? I thought of just
counting the rows in all the tables on both servers, but that only tells
part of the story. Is the a more elegant and complete way? Also, the
servers are separated by a slow WAN link, so transferring the whole
database across the network is not an option.
--
Eric Robinson
Director of Information Technology
Physician Select Management, LLC
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