Re: max_connections and standby server

On Tue, Aug 11, 2015 at 2:42 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Tatsuo Ishii <ishii(at)postgresql(dot)org> writes:
>> I think this is because pg_control on the standby remembers that the
>> previous primary server's max_connections = 1100 even if the standby
>> server fails to start. Shouldn't we update pg_control file only when
>> standby succeeds to start?
>
> Somebody refresh my memory as to why we have this restriction (that is,
> slave's max_connections >= master's max_connections) in the first place?
> Seems like it should not be a necessary requirement, and working towards
> getting rid of it would be far better than any other answer.

If I recall correctly, that's because KnownAssignedXIDs and the lock
table need to be large enough on the standby for the largest snapshot
possible (procarray.c).
--
Michael