Thread: Bugs in superuser_reserved_connections and max_wal_senders vs max_connections

Both superuser_reserved_connections and max_wal_senders can be set to
a value that's higher than max_connections, which is quite pointless,
and annoying :)

The docs for superuser_reserved_connections say "The value must be
less than the value of max_connections.", but this is never enforced.
Well, it's strangely enfocred. With max_connections=100, I can set
superuser_reserved_connections to 103. Looks like this is caused by
autovacuum_max_workers - because if I increase that one to 4, then I
can get it up to104...

The check in PostmasterMain():if (ReservedBackends >= MaxBackends){    write_stderr("%s: superuser_reserved_connections
mustbe less than
 
max_connections\n", progname);    ExitPostmaster(1);}

should probably check against MaxConnections instead of MaxBackends, I think?


The docs for max_wal_senders say nothing at all about the relation to
max_connections, which it really should. And it should probably be
enforced the same way that superuser_reserved_connections is, so you
can't set it to silly high values.

-- Magnus HaganderMe: http://www.hagander.net/Work: http://www.redpill-linpro.com/

Magnus Hagander <magnus@hagander.net> writes:
> The check in PostmasterMain():
>     if (ReservedBackends >= MaxBackends)
>     {
>         write_stderr("%s: superuser_reserved_connections must be less than
> max_connections\n", progname);
>         ExitPostmaster(1);
>     }

> should probably check against MaxConnections instead of MaxBackends, I think?

Yeah, this code probably dates from before there was a difference.

In general, I'd bet that this is not the only place where the wrong one
of those variables is being consulted.
        regards, tom lane

On Thu, Aug 9, 2012 at 4:17 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Magnus Hagander <magnus@hagander.net> writes:
>> The check in PostmasterMain():
>>       if (ReservedBackends >= MaxBackends)
>>       {
>>               write_stderr("%s: superuser_reserved_connections must be less than
>> max_connections\n", progname);
>>               ExitPostmaster(1);
>>       }
>
>> should probably check against MaxConnections instead of MaxBackends, I think?
>
> Yeah, this code probably dates from before there was a difference.

That was my guess as well.


> In general, I'd bet that this is not the only place where the wrong one
> of those variables is being consulted.

Probably :)

I've fixed this issue. Didn't spot another one with a quick check, but
there's quite possibly something hiding somewhere, yes :)

-- Magnus HaganderMe: http://www.hagander.net/Work: http://www.redpill-linpro.com/