Re: Time to up bgwriter_lru_maxpages?

On Wed, Feb 1, 2017 at 9:47 PM, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com> wrote:
> Before doing that the first thing to look at would be why the limit is
> currently INT_MAX / 2 instead of INT_MAX.

Generally the rationale for GUCs with limits of that sort is that
there is or might be code someplace that multiplies the value by 2 and
expects the result not to overflow.

I expect that increasing the maximum value of shared_buffers beyond
what can be stored by an integer could have a noticeable distributed
performance cost for the entire system. It might be a pretty small
cost, but then again maybe not; for example, BufferDesc's buf_id
member would have to get wider, and probably the freeNext member, too.
Andres already did unspeakable things to make a BufferDesc fit into
one cache line for performance reasons, so that wouldn't be great
news.

Anyway, I committed the patch posted here. Or the important line out
of the two, anyway. :-)

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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