Re: Decrease MAX_BACKENDS to 2^16

On 04/28/2014 12:39 PM, Andres Freund wrote:
> On 2014-04-28 10:48:30 +0300, Heikki Linnakangas wrote:
>> On 04/26/2014 09:27 PM, Andres Freund wrote:
>>> 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.
>>
>> It doesn't seem unreasonable to have a database with tens of thousands of
>> connections. Sure, performance will suffer, but if the connections sit idle
>> most of the time so that the total load is low, who cares. Sure, you could
>> use a connection pooler, but it's even better if you don't have to.
>
> 65k connections will be absolutely *disastrous* for performance because
> of the big PGPROC et al.

Well, often that's still good enough.

> The main reason I want to shrink it is that I want to make pin/unpin
> buffer lockless and all solutions I can come up with for that require
> flags to be in the same uint32 as the refcount. For performance
> it'd be beneficial if usagecount also fits in there.

Would it be enough to put only some of the flags in the same uint32?

- Heikki