Thread: Re: [GENERAL] Multiple Indexing, performance impact

Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Strange that even at 1024 performance still drops off at 7.  Seems it
> may be more than buffer thrashing.

Yeah, if anything the knee in the curve seems to be worse at 1024
buffers.  Curious.  Deserves more investigation, perhaps.

This does remind me that I'd been thinking of suggesting that we
raise the default -B to something more reasonable, maybe 1000 or so
(yielding an 8-meg-plus shared memory area).  This wouldn't prevent
people from setting it small if they have a small SHMMAX, but it's
probably time to stop letting that case drive our default setting.
Since 64 is already too much to let 7.1 fit in SHMMAX = 1MB, I think
the original rationale for using 64 is looking pretty broken anyway.
Comments?

            regards, tom lane

Tom Lane writes:

> This does remind me that I'd been thinking of suggesting that we
> raise the default -B to something more reasonable, maybe 1000 or so
> (yielding an 8-meg-plus shared memory area).

On Modern(tm) systems, 8 MB is just as arbitrary and undersized as 1 MB.
So while for real use, manual tuning will still be necessary, on test
systems we'd use significant amounts of memory for nothing, or not start
up at all.

Maybe we could look around what the default limit is these days, but
raising it to arbitrary values will just paint over the fact that user
intervention is still required and that there is almost no documentation
for this.

--
Peter Eisentraut   peter_e@gmx.net   http://funkturm.homeip.net/~peter