On 31.03.2025 22:09, Robert Haas wrote:
Oh, right. I've never really understood why we round off to integers,
but the fact that we don't allow row counts < 1 feels like something
pretty important. My intuition is that it probably helps a lot more
than it hurts, too.
We definitely shouldn’t remove the row counts < 1 check, since there are many places in the planner where we divide by rows. This mechanism was added specifically to prevent division by zero. Also, allowing rows estimates below 1 can sometimes make the planner overly optimistic, leading it to prefer cheaper-looking plans that may not perform well in practice. For example, choosing a Nested Loop instead of a more appropriate Hash Join.
Allowing fractional rows > 1 might help improve planner accuracy in some cases, but this needs further study to fully understand the impact.
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Best regards,
Ilia Evdokimov,
Tantor Labs LLC.
