I noticed your 8/18 commit to address an issue I raised regarding
parameterized limit statements. Specifically, prepared statements with
a variable limit would tend to revert to bitmap or seqscan.
I check out cvs tip and am still getting that behavior :(. So, I had a
look at createplan.c to see what was going on. Inside makelimit, there
is:
if (count_est != 0)
{
double count_rows;
if (count_est > 0)
count_rows = (double) count_est;
else
count_rows = clamp_row_est(lefttree->plan_rows * 0.10);
if (count_rows > plan->plan_rows)
count_rows = plan->plan_rows;
if (plan->plan_rows > 0)
plan->total_cost = plan->startup_cost +
(plan->total_cost - plan->startup_cost)
* count_rows / plan->plan_rows;
plan->plan_rows = count_rows;
if (plan->plan_rows < 1)
plan->plan_rows = 1;
}
Is this correct? plan_rows is assigned (from count_rows) after it is
checked to determine cost. If this is correct, would you like a test
cast demonstrating the behavior?
Merlin
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