clamp_row_est avoid infinite
clamp_row_est avoid infinite
От:
jian he <jian.universality@gmail.com>
Дата:
hi.
/*
* clamp_row_est
* Force a row-count estimate to a sane value.
*/
double
clamp_row_est(double nrows)
{
/*
* Avoid infinite and NaN row estimates. Costs derived from such values
* are going to be useless. Also force the estimate to be at least one
* row, to make explain output look better and to avoid possible
* divide-by-zero when interpolating costs. Make it an integer, too.
*/
if (nrows > MAXIMUM_ROWCOUNT || isnan(nrows))
nrows = MAXIMUM_ROWCOUNT;
else if (nrows <= 1.0)
nrows = 1.0;
else
nrows = rint(nrows);
return nrows;
}
The comments say `Avoid infinite and NaN`
but actually we only avoid NaN.
Do we need to add isinf(nrows)?
Re: clamp_row_est avoid infinite
От:
Tom Lane <tgl@sss.pgh.pa.us>
Дата:
jian he writes: > if (nrows > MAXIMUM_ROWCOUNT || isnan(nrows)) > nrows = MAXIMUM_ROWCOUNT; > else if (nrows <= 1.0) > nrows = 1.0; > else > nrows = rint(nrows); > The comments say `Avoid infinite and NaN` > but actually we only avoid NaN. Really? The IEEE float arithmetic standard says that Inf is greater than any finite value, and in particular it'd be greater than MAXIMUM_ROWCOUNT. regards, tom lane
