[knot-dns-users] Knot 1.6.1 and journal size tuning

Anand Buddhdev anandb at ripe.net
Mon Dec 15 11:16:06 CET 2014

Hi Knot developers,

I've now installed version 1.6.1 on some servers, and I'm observing some
journal related issues, and I have questions about them. First off,
here's one issue:

2014-12-15T06:00:56 info: [203.in-addr.arpa] NOTIFY, incoming, at 53535: received serial 3006121318
2014-12-15T06:00:56 info: [203.in-addr.arpa] refresh, outgoing, at 53: master has newer serial 3006121317 -> 3006121318
2014-12-15T06:00:56 info: [203.in-addr.arpa] IXFR, incoming, at 53: starting
2014-12-15T06:00:57 warning: [203.in-addr.arpa] IXFR, incoming, at 53: failed to write changes to journal (not enough space
2014-12-15T06:00:58 notice: [203.in-addr.arpa] IXFR, incoming, at 53: fallback to AXFR
2014-12-15T06:00:58 info: [203.in-addr.arpa] AXFR, incoming, at 53: starting
2014-12-15T06:00:59 info: [203.in-addr.arpa] AXFR, incoming, at 53: finished, serial 3006121317 -> 3006121318, 0.65 seconds,
171 messages, 7960312 bytes

So it looks like the IXFR is too big, and won't fit into the journal,
and Knot is falling back to AXFR. When I requested this IXFR by hand, I got:

$ dig ixfr=3006121317 203.in-addr.arpa @
;; XFR size: 121779 records (messages 170, bytes 7963389)

The size of the IXFR in bytes is below the configured file size limit
(10M), but I suspect that 7963389 bytes probably take up more room in
the journal, so Knot can't write into it, and is falling back to AXFR.

Are you able to tell me (approximately of course), how much disk space
is required for a given number of bytes of IXFR? This will help me tune
the setting of ixfr-fslimit to avoid this unnecessary fallback to AXFR.

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