Re: Linux kernel impact on PostgreSQL performance

On 01/13/2014 05:48 PM, Andres Freund wrote:
> On 2014-01-13 10:56:00 -0800, Josh Berkus wrote:
>> Well, it was the lack of sysctl options which takes the 2Q change from
>> "annoyance" to "potential disaster". We can't ever get away from the
>> possibility that the Postgres use-case might be the minority use-case,
>> and we might have to use non-default options. It's when those options
>> aren't present *at all* that we're stuck.
>
> Unless I am missing something the kernel's going further *away* from a
> simple 2q system, not the contrary.

Well, they implemented a 2Q system and deliberately offered no sysctl
variables to modify its behavior. Now they're talking about
implementing an ARC system -- which we know the perils of -- again,
without any configuration variables in case the default behavior doesn't
work for everyone. And it's highly unlikely that an ARC which is
designed for desktop and/or file server users -- let alone mobile users
-- is going to be optimal for PostgreSQL out of the box.

In fact, I'd assert that it's flat-out impossible to engineer an ARC
which will work for multiple different use cases without user-level
configuration.

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com