Unnecessary SOA queries upon notify with up to date serial
I've noticed that Knot, even when sent a NOTIFY containing an up to date serial, contacts the master anyway to do a SOA query, and this seems entirely unnecessary. Look at this sequence:
2016-12-16T11:56:31 info: [5.in-addr.arpa.] NOTIFY, incoming, 193.0.19.190@41310: received serial 1481889382
2016-12-16T11:56:31 info: [5.in-addr.arpa.] NOTIFY, incoming, 2001:67c:2e8:11::c100:13be@37020: received serial 1481889382
2016-12-16T11:56:31 info: [5.in-addr.arpa.] refresh, outgoing, 2001:67c:2e8:11::c100:13be@53: master has newer serial 1481889262 -> 1481889382
2016-12-16T11:56:31 info: [5.in-addr.arpa.] IXFR, incoming, 2001:67c:2e8:11::c100:13be@53: starting
2016-12-16T11:56:31 info: [5.in-addr.arpa.] IXFR, incoming, 2001:67c:2e8:11::c100:13be@53: finished, serial 1481889262 -> 1481889382, 0.58 seconds, 301 messages, 5608812 bytes
2016-12-16T11:56:32 info: [5.in-addr.arpa.] zone file updated, serial 1481889262 -> 1481889382
2016-12-16T11:56:43 info: [5.in-addr.arpa.] NOTIFY, incoming, 93.175.159.250@46670: received serial 1481889382
2016-12-16T11:56:43 info: [5.in-addr.arpa.] NOTIFY, incoming, 2001:67c:2d7c:66::53@45871: received serial 1481889382
2016-12-16T11:56:43 info: [5.in-addr.arpa.] refresh, outgoing, 93.175.159.250@53: zone is up-to-date
2016-12-16T11:56:43 info: [5.in-addr.arpa.] refresh, outgoing, 2001:67c:2e8:11::c100:13be@53: zone is up-to-date
At the 31-second mark, Knot received a NOTIFY from one of the masters of 5.in-addr.arpa, with a newer serial. It dutifully refreshed the zone to a new serial. Several seconds later, at the 43-second mark, the other master for the same zone sent a NOTIFY, also with the new serial. This second master is far away, so it is natural that it takes it longer to update and notify its slaves. Knot should see that the NOTIFY was for a serial it already has, and shouldn't waste any cycles or network resources with SOA queries. Do you agree with this assessment?