[Pdns-users] pdns-recursor: Only two threads used when threads=4

[Grace Wang]

Thanks to Winfried and others for the response!

It was indeed the pdns-distributes-queries config that did the trick. My
query file was only 1 query, so all the queries were sent to one thread. I
tried it with a query file with 500 queries, the load was distributed to
all 12 threads evenly.

The latency of version 4.0.3 is much smaller than that of version 3.6.0.

Thanks again,
Grace

On Fri, Oct 21, 2016 at 1:28 AM, abang <abang at t-ipnet.net> wrote:

> Hi Grace,
>
> Since 3.7.0, Recursor distributes queries to the threads itself. See
> https://doc.powerdns.com/md/recursor/settings/#pdns-distributes-queries
>
> Additional it hashes the queries with the goal to send the same query to
> the same thread. This improves the cache hit rate and thus the average
> latency and the overall performance.
>
> I guess your query generator sends only 2 different queries (or more
> queries which lead to only 2 different hash results).
>
> Winfried
>
> Am 21.10.2016 um 09:45 schrieb Øystein Viggen:
>
>> Grace Wang <xiaohong.grace.wang at gmail.com> writes:
>>
>> I installed pdns-recursor 4.0.3 on a CentOS 6.5 box, that has 20 physical
>>>> cores and 128G RAM. When I set the threads in /etc/pdns-recursor/
>>>> recursor.conf to be 4 or 12, then issued tons of queries (one query sent
>>>> multiple times using multiple dnsperf instances simultaneously) at it, I
>>>> noticed only 2 of the threads were working actively, each using almost
>>>> 100%
>>>> CPU and ~90% CPU, respectively. The other threads were using 0% CPU.
>>>>
>>> Could it be that pdns-recursor isn't optimized very well for serving the
>> same same query at a very high rate?
>>
>> With about 2000 queries/second of real-world DNS traffic from servers
>> and users, I'm seeing a good spread of the load over 24 threads on
>> pdns-recursor 4.0.3.  (Ubuntu 16.04, if that matters).
>>
>> Øystein
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>
>
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