On Mon, Jun 20, 2016 at 12:24 PM, Masahiko Sawada <sawada.m...@gmail.com> wrote: > > > In following case, it look to me that no one collect the tuple. > But it's obviously incorrect, this query collects a tuple(aid = 10) actually. > > postgres(1)=# explain analyze verbose select * from pgbench_accounts > where aid = 10; > QUERY PLAN > -------------------------------------------------------------------------------------------------------------------------------------------- > Gather (cost=1000.00..217018.43 rows=1 width=97) (actual > time=0.541..2094.773 rows=1 loops=1) > Output: aid, bid, abalance, filler > Workers Planned: 2 > Workers Launched: 2 > -> Parallel Seq Scan on public.pgbench_accounts > (cost=0.00..216018.34 rows=0 width=97) (actual time=1390.109..2088.103 > rows=0 loops=3) > Output: aid, bid, abalance, filler > Filter: (pgbench_accounts.aid = 10) > Rows Removed by Filter: 3333333 > Worker 0: actual time=2082.681..2082.681 rows=0 loops=1 > Worker 1: actual time=2087.532..2087.532 rows=0 loops=1 > Planning time: 0.126 ms > Execution time: 2095.564 ms > (12 rows) > > How can we consider actual rows and nloops? >
Here rows is an average value per-execution. In some cases, you might not get the exact number. You might find the information in docs [1] useful. Refer Explain Analyze section. [1] - https://www.postgresql.org/docs/9.6/static/using-explain.html With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
