sql - PostgreSQL 10 - IN 和任何性能莫名其妙的行为

Question

我从大表中进行选择，其中 id 在数组/列表中。 检查了几个变体，结果让我感到惊讶。

<强>1。使用 ANY 和 ARRAY

EXPLAIN (ANALYZE,BUFFERS)
SELECT * FROM cca_data_hours
    WHERE
    datetime = '2018-01-07 19:00:00'::timestamp without time zone AND
    id_web_page = ANY (ARRAY[1, 2, 8, 3 /* ~50k ids */])

结果

"Index Scan using cca_data_hours_pri on cca_data_hours  (cost=0.28..576.79 rows=15 width=188) (actual time=0.035..0.998 rows=6 loops=1)"
"  Index Cond: (datetime = '2018-01-07 19:00:00'::timestamp without time zone)"
"  Filter: (id_web_page = ANY ('{1,2,8,3, (...)"
" Rows Removed by Filter: 5"
"  Buffers: shared hit=3"
"Planning time: 57.625 ms"
"Execution time: 1.065 ms"

---

<强>2。使用 IN 和 VALUES

EXPLAIN (ANALYZE, BUFFERS)
SELECT * FROM cca_data_hours
    WHERE
    datetime = '2018-01-07 19:00:00'::timestamp without time zone AND
    id_web_page IN (VALUES (1),(2),(8),(3) /* ~50k ids */)

结果

"Hash Join  (cost=439.77..472.66 rows=8 width=188) (actual time=90.806..90.858 rows=6 loops=1)"
"  Hash Cond: (cca_data_hours.id_web_page = "*VALUES*".column1)"
"  Buffers: shared hit=3"
"  ->  Index Scan using cca_data_hours_pri on cca_data_hours  (cost=0.28..33.06 rows=15 width=188) (actual time=0.035..0.060 rows=11 loops=1)"
"        Index Cond: (datetime = '2018-01-07 19:00:00'::timestamp without time zone)"
"        Buffers: shared hit=3"
"  ->  Hash  (cost=436.99..436.99 rows=200 width=4) (actual time=90.742..90.742 rows=4 loops=1)"
"        Buckets: 1024  Batches: 1  Memory Usage: 9kB"
"        ->  HashAggregate  (cost=434.99..436.99 rows=200 width=4) (actual time=90.709..90.717 rows=4 loops=1)"
"              Group Key: "*VALUES*".column1"
"              ->  Values Scan on "*VALUES*"  (cost=0.00..362.49 rows=28999 width=4) (actual time=0.008..47.056 rows=28999 loops=1)"
"Planning time: 53.607 ms"
"Execution time: 91.681 ms"

---

我希望案例 #2 会更快，但事实并非如此。 为什么 IN with VALUES 很慢？

Answer 1

比较 EXPLAIN ANALYZE 结果，在给定的示例中，旧版本似乎没有使用 key 的可用索引。 ANY (ARRAY[]) 变得更快的原因在于版本 9.2 https://www.postgresql.org/docs/current/static/release-9-2.html

Allow indexed_col op ANY(ARRAY[...]) conditions to be used in plain index scans and index-only scans (Tom Lane)

您从中获得建议的站点是关于版本 9.0