[Pdns-users] Error with master slave replication
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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