Re: Calculating statistic via function rather than with query is slowing my query

On 18/08/2011 9:03 AM, Anish Kejariwal wrote:
> Thanks for the help Pavel and Craig.  I really appreciate it.  I'm
> going to try a couple of these different options (write a c function,
> use a sql function with case statements, and use plperl), so I can see
> which gives me the realtime performance that I need, and works best
> for clean code in my particular case.
Do you really mean "realtime"? Or just "fast"?

If you have strongly bounded latency requirements, any SQL-based,
disk-based system is probably not for you. Especially not one that
relies on a statics-based query planner, caching, and periodic
checkpoints. I'd be looking into in-memory databases designed for
realtime environments where latency is critical.

Hard realtime: If this system fails to respond within <x> milliseconds,
all the time, every time, then something will go "smash" or "boom"
expensively and unrecoverably.

Soft realtime: If this system responds late, the late response is
expensive or less useful. Frequent late responses are unacceptable but
the occasional one might be endurable.

Just needs to be fast: If it responds late, the user gets irritated
because they're sitting and waiting for a response. Regular long stalls
are unacceptable, but otherwise the user can put up with it. You're more
concerned with average latency than maximum latency.

--
Craig Ringer