[Pdns-dev] PowerDNS 4, Remote and threading

[Aki Tuomi]

On Sun, Sep 11, 2016 at 06:23:05PM +0300, Viktor Velchev wrote:
> Hello,
> 
> I am running PowerDNS 4.0.1, which is complied from source with ZeroMQ
> support in a Debian 8 environment. I am experimenting with Remote and I am
> willing to write my own DNS storage (back-end), which connects to PowerDNS
> through Remote. Changelogs for the newer PowerDNS versions do not give any
> hints regarding the bellow described problem, so I think it is safe to
> assume that the case will be the same with all available 4.0.x releases.
> 
> I am launching a single Remote instance and several threads:
> launch=remote
> distributor-threads=4
> receiver-threads=4
> 
> Receiver and distributor thread count is just an example, the point is that
> I am not running in single threaded mode.
> 
> The main problem is that Remote itself does not give me any options to
> create a multi-threaded back-end. I have checked the source and although
> ZeroMQ is configured to start two I/O threads, but the implemented REQ/REP
> pattern limits the communication to:
> 
> 1. PowerDNS sends a request about a domain.
> 2. PowerDNS waits (blocks) until it receives data about the domain.
> 
> Once my back-end receives a request I am limited to either returning false
> or replying.
> I am pretty sure that the case is the same with the Unix socket connector.
> I have NOT checked if the case is the same with the HTTP connector.
> 
> My questions are:
> 1. Is there a possibility to modify the communication pattern, so that
> PowerDNS either submits multiple requests through Remote OR maybe add a
> command which asks for a new query while the previous one is being executed?
> 2. In case I have myself misunderstood the way PowerDNS operates, is there
> a Remote connector which is suited for use in cases where the recipient
> wants to handle multiple requests at a time?
> 
> Best Regards,
> Victor

Usually powerdns launches several backend threads, each working in blocking
mode. Thus you will have concurrent requests running despite remotebackend
only doing one request at a time.

Aki