On 2022-Aug-10, Richard Guo wrote:
> The right-anti join plan has the same cost estimation with right join
> plan in this case. So would you please help to test what the right join
> plan looks like in your env for the query below?
>
> select * from foo left join bar on foo.a = bar.c;
You're right, it does.
55432 16devel 475322=# explain (analyze, buffers) select * from foo left join
bar on foo.a = bar.c;
QUERY PLAN
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Hash Right Join (cost=1.23..90875.24 rows=10 width=20) (actual
time=456.410..456.415 rows=10 loops=1)
Hash Cond: (bar.c = foo.a)
Buffers: shared hit=15852 read=6273
-> Seq Scan on bar (cost=0.00..72124.00 rows=5000000 width=12) (actual
time=0.036..210.468 rows=5000000 loops=1)
Buffers: shared hit=15852 read=6272
-> Hash (cost=1.10..1.10 rows=10 width=8) (actual time=0.037..0.038
rows=10 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 9kB
Buffers: shared read=1
-> Seq Scan on foo (cost=0.00..1.10 rows=10 width=8) (actual
time=0.022..0.026 rows=10 loops=1)
Buffers: shared read=1
Planning:
Buffers: shared hit=92 read=13
Planning Time: 1.077 ms
Execution Time: 456.458 ms
(14 filas)
55432 16devel 475322=# explain (analyze, buffers) select * from foo left join
bar on foo.a = bar.c where bar.c is null;
QUERY PLAN
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Hash Right Anti Join (cost=1.23..90875.24 rows=10 width=20) (actual
time=451.747..451.751 rows=10 loops=1)
Hash Cond: (bar.c = foo.a)
Buffers: shared hit=15646 read=6479
-> Seq Scan on bar (cost=0.00..72124.00 rows=5000000 width=12) (actual
time=0.048..204.940 rows=5000000 loops=1)
Buffers: shared hit=15645 read=6479
-> Hash (cost=1.10..1.10 rows=10 width=8) (actual time=0.030..0.031
rows=10 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 9kB
Buffers: shared hit=1
-> Seq Scan on foo (cost=0.00..1.10 rows=10 width=8) (actual
time=0.017..0.020 rows=10 loops=1)
Buffers: shared hit=1
Planning Time: 0.227 ms
Execution Time: 451.793 ms
--
Álvaro Herrera Breisgau, Deutschland — https://www.EnterpriseDB.com/
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