Yeah, that's what I figured too, but I wasn't quite sure of the behavior. After some experimenting I'm more sure of what I'm seeing now so I'll report it as a bug.

Jay

On Tue, 2 Jan 2018, Alan Clegg wrote:
Looks like something that ISC would like to have logged as a bug...  And
a perfect thing to find in rc1. 8-)

AlanC

On 1/2/18 3:00 PM, Jay Ford wrote:
I'm having some odd trouble with DNSTAP output file rolling in BIND
9.12.0rc1.

I have named built like:
   BIND 9.12.0rc1 <id:f9c3aba>
   running on Linux x86_64 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt25-1
(2016-03-06)
   built by make with 'STD_CDEFINES=-DISC_FACILITY=LOG_LOCAL5'
'--libdir=/usr/lib/x86_64-linux-gnu' '--with-openssl' '--enable-dnstap'
'--enable-fixed-rrset' '--disable-openssl-version-check'
'--with-libtool' '--enable-dnsrps'
   compiled by GCC 6.3.0 20170516
   compiled with OpenSSL version: OpenSSL 1.1.0f  25 May 2017
   linked to OpenSSL version: OpenSSL 1.1.0f  25 May 2017
   compiled with libxml2 version: 2.9.4
   linked to libxml2 version: 20904
   threads support is enabled

I have DNSTAP configured like:
   dnstap {
      client query;
   };
   dnstap-output file "tmp/dnstap.out" versions 10 size 10m;

It mostly works as expected, except that named:
   o  logs twice about rolling the file every time, such as:
         Jan  2 05:15:42 named[24758]: dnstap: info: rolling dnstap
            destination 'tmp/dnstap.out'
         Jan  2 05:15:42 named[24758]: dnstap: info: rolling dnstap
            destination 'tmp/dnstap.out'
   o  sometimes crashes after logging that, possibly after rolling the file
   o  writes to multiple output files simultaneously, such as:
         ls -lt dnstap* | head -2
         -rw-r--r-- 1 bind bind  1282048 Jan  2 16:24 dnstap.out
         -rw-r--r-- 1 bind bind  1273856 Jan  2 16:24 dnstap.out.0
      & 2 minutes later:
         ls -lt dnstap* | head -2
         -rw-r--r-- 1 bind bind  1286144 Jan  2 16:26 dnstap.out
         -rw-r--r-- 1 bind bind  1277952 Jan  2 16:26 dnstap.out.0

This system had 4 worker threads in use.  Another similar system with
only 1 thread does not have such trouble, which got me wondering about
problems with threads & DNSTAP, specifically output file rolling. 
Reducing the threads on the afflicted system (via named option "-n 1")
seems to avoid the problem, but it's a little early to tell, & it's not
a desirable fix.

I'd appreciate it if somebody who knows the code would comment on the
threads vs DNSTAP possibility or point me in some other direction to
figure this out.

I have a named core file & can provide more config... details if required.

________________________________________________________________________
Jay Ford, Network Engineering Group, Information Technology Services
University of Iowa, Iowa City, IA 52242
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