[Pdns-users] Error with master slave replication

Bill Pitz bill at pitz.net
Thu Aug 27 23:01:47 UTC 2009

> Is it possible to 'force' the error by issueing a:
> dig +tcp @<masternameserver ip> xyzzy.net AXFR
> The error indicates a problem in tcp-connections to the supermaster.

Thanks for your reply.  It is not possible to reproduce the error by 
doing manual zone transfers with dig or host.  These work and complete 
successfully, every time, within a few seconds.

When the pdns server does the AXFRs, it takes longer (30+ seconds) and 
then fails with the error I originally posted.  I ran some packet 
captures as well, and it appears that the transmit window on the master 
server fills up, there are some packets with adjusted window size, and 
then the transfer fails.

This leads to my next question:

When the backend on the slave is PostgreSQL, how does the AXFR process 
actually work?  Is the zone loaded into a buffer in the slave pdns 
server and then inserted into the database, or does it attempt to insert 
it into the database in real time?  It seems like the size of the zone 
causes some delay in the completion of the database insert (since the 
full zone transfer for powerdns takes 40+ seconds when it is successful, 
while it only takes 4-5 seconds with dig or host) and this ultimately 
triggers some sort of timeout on the master server that causes it to 
dump the connection.



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