Re: Decrease MAX_BACKENDS to 2^16

Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> On 2014-04-26 11:52:44 +0100, Greg Stark wrote:
>> But I don't think it's beyond the realm of possibility
>> that we'll reduce the overhead in the future with an eye to being able
>> to do that. Is it that helpful that it's worth baking in more
>> dependencies on that limitation?

> What I think it's necessary for is at least:

> * Move the buffer content lock inline into to the buffer descriptor,
> while still fitting into one cacheline.
> * lockless/atomic Pin/Unpin Buffer.

TBH, that argument seems darn weak, not to mention probably applicable
only to current-vintage Intel chips. And you have not proven that
narrowing the backend ID is necessary to either goal, even if we
accepted that these goals were that important.

While I agree with you that it seems somewhat unlikely we'd ever get
past 2^16 backends, these arguments are not nearly good enough to
justify a hard-wired limitation.

regards, tom lane