With all due respect to Monty (and I mean that — much respect is due), I have some serious issues with his portrayal of the 5.1 release.  I hate to make my first entry on Planet MySQL about a controversy, but he encouraged people to blog about their experience with 5.1, so that’s what I’ll do here.

Overall Quality

As a long time user, I am very confident that the quality of 5.1 GA far exceeds that of the initial 5.0 GA release (5.0.15).  In fact, I would go further and suggest that the MySQL organization has if anything been too conservative about declaring 5.1 GA.

It’s obviously true that there are still many bugs open.  However no software is bug free, especially not those with codebase as large as MySQL.  So the question is not if they are bug free, but are the …

A typical scenario is when a master has a few dozen slaves, and instead of dealing with all of them directly, uses four relay slaves, each one dealing with 6 slaves.
So, where's the trick? The trouble comes if you change replication format after you start the slave.
Example. One master (M), two relay slaves (R1, R2), with four slaves each …

For example, after executing this code:

create table t1 (id int, c char(10), d date);
insert into t1 values (1, 'abc', '2008-01-01');
insert into t1 values (2, 'def', '2008-08-19');
insert into t1 values (3, 'ghi', current_date());
select * from t1; …