What does `iterate_query` for SQL want as output?

[Coy Hile]

> 
> Did you check your logs?
> 

that’s just it. There’s nothing in syslog (which is logging at mail.debug). Not just nothing useful, absolutely _nothing_ logged when I run that. All I see is this (printed, I presume to STDERR):

doveadm backup -D -A -R -f ssh -i id_rsa.dsync imap01.coyhile.com /opt/local/bin/doveadm dsync-server -A
Error: User listing returned failure
doveadm: Error: Failed to iterate through some users
dsync-local(hile at coyhile.com)<gCspG6m8Tl3bJQEAxHAMlw>: Error: read(remote) failed: EOF (version not received)

The last line makes sense given the earlier failure.

Should this log somewhere else besides syslog? And is there some way I can isolate and test _just_ the user iteration and enumeration code to prove out that the query is correct? Clearly, from output above, it should be.

Thanks,
-c