queries fail when mysql replication consumes CPU on large zones

We've had an installation where the nameserver stopped responding to
queries because mysql replication was consuming 100% of the CPU

$ named -V
BIND 9.9.5 (Extended Support Version) <id:f9b8a50e> built by make with
'--prefix=/usr/local/bind-dlz' '--with-openssl' '--with-dlz-mysql=yes'
'--with-dlz-stub=yes' '--with-dlz-filesystem=yes'
'--disable-openssl-version-check' '--enable-rrl'
compiled by GCC 4.4.5

The problem was a large zone updating frequently (40,000+ records at a
time) caused the remote mysql slaving  replication on the bind-dlz
installation to consume 100% of the CPU, having the effect of causing
dns queries to that node timing out.

Is this more of a mysql optimization issue or is there something to be
done within bind-dlz that can mitigate against the possibility of the
nameserver itself being crowded out by the mysql daemon for any reason
(not just this particular case)

Thank you.




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