delay between nsupdate and NOTIFY

[Charles Musser]

> 
> Adjust serial-query-rate.  This also controls the notify rate in BIND 9.9.
> A seperate control "notify-rate" is coming in BIND 9.11.
> 
Today we tried increasing serial-query-rate from our original value of 1000 up to 5000 for a while, and then up to 10000. The symptoms (long delay for NOTIFY, lots of deferred transfers) didn't go away. 

Looking at a graph of some historical data query types (we use DSC for data collection), we notice a fairly dramatic drop off in NOTIFY messages on the day we changed the version from 9.7.3 to 9.9.7. So maybe the upgrade was significant. During the upgrade, we didn't change BIND's configuration, only the version.

One thing we might try is going back to an earlier BIND. Not sure if any files generated by the upgrade are backwards compatible with the original version, so we'll have to consider that before we make such a move.

Chuck