On Thu, 6 Mar 2025 at 14:18, Alena Rybakina <a.rybak...@postgrespro.ru> wrote: > > Hi! I got a query plan with a strange number of rows. Could you please > help me understand it? > > To be honest I can't understand why 0.50 number of rows here?
Because the scan matched only ~(500 rows over 999 iterations = 500/999 ~=) 0.50 rows for every loop, on average, for these plan nodes: > -> Nested Loop (actual rows=0.50 loops=999) > -> Seq Scan on tb (actual rows=0.50 loops=999) And for this, it was 500 rows total in 1000 iterations, which also rounds to 0.50: > SubPlan 2 > -> Result (actual rows=0.50 loops=1000) > One-Time Filter: ((ta1.id < 1000) AND (InitPlan 1).col1) As of ddb17e38 (and its follow-up 95dbd827), we display fractional rows-per-loop, with 2 digits of precision, rather than a rounded integer. This allows a user to distinguish plan nodes with 0.49 rows/loop and 0.01 rows/loop, and that can help inform the user about how to further optimize their usage of indexes and other optimization paths. Kind regards, Matthias van de Meent Neon (https://neon.tech)
