Re: Decrease MAX_BACKENDS to 2^16

On 2014-04-26 11:22:39 -0400, Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > On 2014-04-26 05:40:21 -0700, David Fetter wrote:
> >> Out of curiosity, where are you finding that a 32-bit integer is
> >> causing problems that a 16-bit one would solve?
>
> > Save space? For one it allows to shrink some structs (into one
> > cacheline!).
>
> And next week when we need some other field in a buffer header,
> what's going to happen? If things are so tight that we need to
> shave a few bits off backend IDs, the whole thing is a house of
> cards anyway.

The problem isn't so much that we need the individual bits, but that we
need something that has an alignment of two, instead of 4.

I don't think we need to decide this without benchmarks proving the
benefits. I basically want to know whether somebody has an actual
usecase - even if I really, really, can't think of one - of setting
max_connections even remotely that high. If there's something
fundamental out there that'd make changing the limit impossible, doing
benchmarks wouldn't be worthwile.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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