Thomas Kellerer <spam_eater@xxxxxxx> writes: > Consider the following execution plan: > ... > -> Aggregate (cost=26.87..26.87 rows=1 width=32) (actual time=0.012..0.012 rows=1 loops=700000) > -> Bitmap Heap Scan on orders o2 (cost=3.45..26.85 rows=8 width=8) (actual time=0.004..0.008 rows=8 loops=700000) > -> Bitmap Index Scan on orders_customer_id_order_date_idx (cost=0.00..3.45 rows=8 width=0) (actual time=0.003..0.003 rows=8 loops=700000) > My expectation would have been that the "Aggregate" step shows the actual time as a product of the number of loops. No, that looks fine to me. The rule of thumb for reading this is total time spent in/below this node is "actual time" times "number of loops". It seems a bit odd that the Agg node would account for a third of the total execution time when it's only processing 8 rows on average ... but maybe it's a really expensive aggregate. Another thought is that the EXPLAIN ANALYZE instrumentation itself can account for significant per-node-invocation overhead. If the total execution time drops significantly when you add "timing off" to the EXPLAIN options, then that's probably a factor in making the Agg node look relatively expensive. regards, tom lane
