Jon Emord <jon@xxxxxxxxxxxx> writes: > -> Index Only Scan using entity_data_model_id_primary_key_uniq on entity (cost=0.70..873753.60 rows=15581254 width=31) (actual time=0.093..2712.836 rows=100 loops=1) > Index Cond: ((ROW(data_model_id, primary_key) >= ROW(123, 'ABC'::text)) AND (ROW(data_model_id, primary_key) <= ROW(123, 'DEF'::text))) > Heap Fetches: 4 > Buffers: shared hit=97259 > 2. > data_model_id = 123 is the 15 most common value of data_model_id with 10.8 million records Hm. I think your answer is in this comment in nbtree's key-preprocessing logic: * Row comparison keys are currently also treated without any smarts: * we just transfer them into the preprocessed array without any * editorialization. We can treat them the same as an ordinary inequality * comparison on the row's first index column, for the purposes of the logic * about required keys. That is, for the purposes of deciding when the index scan can stop, the "<= ROW" condition acts like "data_model_id <= 123". So it will run through all of the data_model_id = 123 entries before stopping. regards, tom lane
