Tom Lane wrote:
"Greg Sabino Mullane" <[EMAIL PROTECTED]> writes:

N.B. My own personal starting default is 2, but I thought 3 was a nice
middle ground more likely to reach consensus here. :)

Your argument seems to be "this produces nice results for me", not
"I have done experiments to measure the actual value of the parameter
and it is X".  I *have* done experiments of that sort, which is where
the default of 4 came from.  I remain of the opinion that reducing
random_page_cost is a band-aid that compensates (but only partially)
for problems elsewhere.  We can see that it's not a real fix from
the not-infrequent report that people have to reduce random_page_cost
below 1.0 to get results anywhere near local reality.  That doesn't say
that the parameter value is wrong, it says that the model it's feeding
into is wrong.

I would like to second that. A while back I performed a number of experiments on differing hardware and came to the conclusion that *real* random_page_cost was often higher than 4 (like 10-15 for multi-disk raid systems).

However I have frequently adjusted Pg's random_page_cost to be less than 4 - if it helped queries perform better.

So yes, it looks like the model is the issue - not the value of the parameter!



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