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

Jan Kadlec jan.kadlec at nic.cz
Mon Dec 15 13:08:36 CET 2014


Hello Anand,

moreover, there is no domain name compression in the journal, I think 
this is the main case of size difference you're seeing.

Regards,

Jan.

On 12/15/2014 12:59 PM, Marek Vavruša wrote:
> Hi Anand,
>
> In general, transfer size is roughly equal to actual stored size with
> the addition of file header and entry descriptors.
> That being said, there's some overhead per stored RR (~16B per record,
> or so CC @jan.kadlec) since the RRs aren't merged into RRSets to keep
> ordering and such.
> But as a rule of thumb, you should allow at least twice the desired
> maximum transfer size for a journal size for two reasons:
> - the journal will be able to keep history of at least one transfer back
> - won't need to flush the zone file after each change (helps to avoid
> disk usage spikes)
>
> Best,
> Marek
>
>
> On 15 December 2014 at 11:16, Anand Buddhdev <anandb at ripe.net> wrote:
>> 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,
>> 193.0.0.198 at 53535: received serial 3006121318
>> 2014-12-15T06:00:56 info: [203.in-addr.arpa] refresh, outgoing,
>> 193.0.0.198 at 53: master has newer serial 3006121317 -> 3006121318
>> 2014-12-15T06:00:56 info: [203.in-addr.arpa] IXFR, incoming,
>> 193.0.0.198 at 53: starting
>> 2014-12-15T06:00:57 warning: [203.in-addr.arpa] IXFR, incoming,
>> 193.0.0.198 at 53: failed to write changes to journal (not enough space
>> provided)
>> 2014-12-15T06:00:58 notice: [203.in-addr.arpa] IXFR, incoming,
>> 193.0.0.198 at 53: fallback to AXFR
>> 2014-12-15T06:00:58 info: [203.in-addr.arpa] AXFR, incoming,
>> 193.0.0.198 at 53: starting
>> 2014-12-15T06:00:59 info: [203.in-addr.arpa] AXFR, incoming,
>> 193.0.0.198 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 @193.0.0.198
>> ...
>> ...
>> ;; 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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