WHERE 子句的不同组合的索引策略，包括。文本模式

Question

这里继续其他问题：

执行以下查询时，它命中了我在 datelocal、views、impressions、gender、agegroup 字段上创建的复合索引：

SELECT date_part('hour', datelocal)                AS hour
     , SUM(views) FILTER (WHERE gender = 'male')   AS male
     , SUM(views) FILTER (WHERE gender = 'female') AS female
FROM   reportimpression
WHERE  datelocal >= '2019-02-01' AND datelocal <  '2019-03-01'
GROUP  BY 1
ORDER  BY 1;

但是，我还希望能够根据 WHERE 中的附加子句过滤此查询，例如：

SELECT date_part('hour', datelocal)                AS hour
     , SUM(views) FILTER (WHERE gender = 'male')   AS male
     , SUM(views) FILTER (WHERE gender = 'female') AS female
FROM   reportimpression
WHERE  datelocal >= '2019-02-01' AND datelocal <  '2019-03-01'
AND network LIKE '%'
GROUP  BY 1
ORDER  BY 1;

第二个查询比第一个慢得多，尽管它应该在少得多的记录上运行，而且它没有命中我的索引。

Table 架构：

CREATE TABLE reportimpression (
    datelocal timestamp without time zone,
    devicename text,
    network text,
    sitecode text,
    advertisername text,
    mediafilename text,
    gender text,
    agegroup text,
    views integer,
    impressions integer,
    dwelltime numeric
);

-- Indices -------------------------------------------------------

CREATE INDEX reportimpression_datelocal_index ON reportimpression(datelocal timestamp_ops);
CREATE INDEX reportimpression_viewership_index ON reportimpression(datelocal timestamp_ops,views int4_ops,impressions int4_ops,gender text_ops,agegroup text_ops);
CREATE INDEX reportimpression_test_index ON reportimpression(datelocal timestamp_ops,(date_part('hour'::text, datelocal)) float8_ops);

分析输出：

Finalize GroupAggregate  (cost=1005368.37..1005385.70 rows=3151 width=24) (actual time=70615.636..70615.649 rows=24 loops=1)
  Group Key: (date_part('hour'::text, datelocal))
  ->  Sort  (cost=1005368.37..1005369.94 rows=3151 width=24) (actual time=70615.631..70615.634 rows=48 loops=1)
        Sort Key: (date_part('hour'::text, datelocal))
        Sort Method: quicksort  Memory: 28kB
        ->  Gather  (cost=1005005.62..1005331.75 rows=3151 width=24) (actual time=70615.456..70641.208 rows=48 loops=1)
              Workers Planned: 1
              Workers Launched: 1
              ->  Partial HashAggregate  (cost=1004005.62..1004016.65 rows=3151 width=24) (actual time=70613.132..70613.152 rows=24 loops=2)
                    Group Key: date_part('hour'::text, datelocal)
                    ->  Parallel Seq Scan on reportimpression  (cost=0.00..996952.63 rows=2821195 width=17) (actual time=0.803..69876.914 rows=2429159 loops=2)
                          Filter: ((datelocal >= '2019-02-01 00:00:00'::timestamp without time zone) AND (datelocal < '2019-03-01 00:00:00'::timestamp without time zone) AND (network ~~ '%'::text))
                          Rows Removed by Filter: 6701736
Planning time: 0.195 ms
Execution time: 70641.349 ms

我是否需要创建额外的索引、调整我的 SELECT 或其他完全不同的东西？

Answer 1

您添加的谓词使用 LIKE 运算符：

AND network LIKE '%'

实际查询计划取决于您传递的内容而不是“%”。但是，一般来说，普通的 btree 索引对此毫无用处。您将需要三元组索引或使用文本搜索基础设施或类似设施，具体取决于您可能要寻找的模式。

参见：

PostgreSQL LIKE query performance variations
Pattern matching with LIKE, SIMILAR TO or regular expressions in PostgreSQL

您甚至可以组合多种索引策略。示例：

如果应该是：

AND network = '<input_string>'

那么，一定要实际使用 = 运算符，而不是 LIKE。按重要性升序排列的原因：

更短
减少混淆
使 Postgres 规划器的工作更简单（非常便宜）
正确

如果您不小心传递了一个包含特殊字符的字符串，您可能会得到不正确的结果。参见：
- Escape function for regular expression or LIKE patterns

WHERE 子句的不同组合的索引策略，包括。文本模式

Indexing strategy for different combinations of WHERE clauses incl. text patterns

postgresql

indexing

postgresql-performance