[Pdns-users] pdns-server 4.0.0 alpha2 mysql query errors

[Brian Candler]

We have just installed a pair of servers with Ubuntu 16.04, with the 
pdns packages from the default Ubuntu repositories, which contain 4.0.0 
alpha 2 [^1]

Unfortunately I am hitting a problem which was already reported back in 
March:

May 17 08:33:50 ns1 pdns[1420]: Backend reported condition which 
prevented lookup (GSQLBackend lookup query: Attempt to bind more 
parameters than query has: SELECT 
content,ttl,prio,type,domain_id,disabled,name,auth FROM records WHERE 
disabled=0 and type=? and name=?) sending out servfail

The original report was here:

https://mailman.powerdns.com/pipermail/pdns-users/2016-March/024085.html

However it doesn't show any resolution to the problem, other than to 
restart the servers. This does fix the problem, but for how long?

These servers had been up for 23 hours before I started testing them 
with dig, and those tests consistently gave SERVFAIL. But logs show the 
first mysql error first occured just under 6 hours after the server started:

May 16 09:26:26 ns1 systemd[1]: Started PowerDNS Authoritative Server.
May 16 09:26:26 ns1 pdns[1420]: PowerDNS Authoritative Server 
4.0.0-alpha2 (C) 2001-2016 PowerDNS.COM BV
May 16 09:26:26 ns1 pdns[1420]: PowerDNS comes with ABSOLUTELY NO 
WARRANTY. This is free software, and you are welcome to redistribute it 
according to the terms of the GPL version 2.
...
May 16 15:24:08 ns1 pdns[1420]: Backend reported condition which 
prevented lookup (GSQLBackend lookup query: Could not execute mysql 
statement: SELECT content,ttl,prio,type,domain_id,disabled,name,auth 
FROM records WHERE disabled=0 and type=? and name=?: Lost connection to 
MySQL server during query) sending out servfail

Notice that was a different error ("Lost connection to MySQL server 
during query" rather than "Attempt to bind more parameters than query has")

This rings a bell. Mysql times out idle connections:
http://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_wait_timeout
However this is after 8 hours, not 6 hours, so this is almost certainly 
a red herring.

mysql> select @@wait_timeout;
+----------------+
| @@wait_timeout |
+----------------+
|          28800 |
+----------------+
1 row in set (0.00 sec)

Unfortunately we have only limited time to help debug this, as the name 
service needs to be up and running ASAP. I'll probably have to replace 
with the 3.4.8 packages from https://www.powerdns.com/downloads.html

Regards,

Brian Candler.

[^1] Why does a long term support OS have an alpha version of pdns? 
Presumably they expect 4.0.0 to become stable very soon.