Re: Priority table or Cache table

On 5/16/14, 8:15 AM, Hans-Jürgen Schönig wrote:

> On 20 Feb 2014, at 01:38, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I am really dubious that letting DBAs manage buffers is going to be
>> an improvement over automatic management.
>
> the reason for a feature like that is to define an area of the application which needs more predictable runtime behaviour.
> not all tables are created equals in term of importance.
>
> example: user authentication should always be supersonic fast while some reporting tables might gladly be forgotten even if they happened to be in use recently.
>
> i am not saying that we should have this feature.
> however, there are definitely use cases which would justify some more control here.
> otherwise people will fall back and use dirty tricks sucks as “SELECT count(*)” or so to emulate what we got here.

Which is really just an extension of a larger problem: many applications do not care one iota about ideal performance; they care about *always* having some minimum level of performance. This frequently comes up with the issue of a query plan that is marginally faster 99% of the time but sucks horribly for the remaining 1%. Frequently it's far better to chose a less optimal query that doesn't have a degenerate case.
--
Jim C. Nasby, Data Architect jim(at)nasby(dot)net
512.569.9461 (cell) http://jim.nasby.net