Re: max_connections and standby server

Michael Paquier <michael(dot)paquier(at)gmail(dot)com> writes:
> On Tue, Aug 11, 2015 at 2:42 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> 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).

Hm. Surely KnownAssignedXIDs could be resized at need. As for the shared
lock table on the standby, that could be completely occupied by locks
taken by hot-standby backend processes, so I don't see why we're insisting
on anything particular as to its size.

regards, tom lane