PG索引失效/生效分析

2023-12-09 18:06:21

PG索引失效/生效分析

索引失效场景

1、任何计算、函数、类型转换 2、!=、<> 3、IS NULL或者IS NOT NULL。类似导致索引失效的还有NOT IN，NOT LIKE等，但是NOT EXISTS不会导致索引失效。 4、模糊查询通配符在开头 5、索引字段在表中占比较高 6、多字段btree索引查询条件不包含第一列 7、在WHERE中使用OR时，有一个列没有索引，那么其它列的索引将不起作用 8、多字段索引查询条件使用OR 在索引列上进行大于大于这类的比较后，这个列的索引是有效的，但是其后的索引将失效

jsonb字段索引分析（json支持GIN索引结构）

1.索引创建jsonb_ops操作符

-- ----------------------------
-- Indexes structure for table tb_security_event
-- ----------------------------
CREATE INDEX "notification_index" ON "public"."tb_security_event" USING gin (
  "notification" "pg_catalog"."jsonb_ops"
);

索引分析执行SQL:

explain analyze verbose SELECT
	securityev0_.ID AS id1_35_,
	securityev0_.application AS applicat2_35_,
	securityev0_.asset AS asset3_35_,
	securityev0_.cia_level AS cia_leve4_35_,
	securityev0_.component AS componen5_35_,
	securityev0_.correlation_info AS correlat6_35_,
	securityev0_.device_ip AS device_i7_35_,
	securityev0_.event_change AS event_ch8_35_,
	securityev0_.event_id AS event_id9_35_,
	securityev0_.event_type AS event_t10_35_,
	securityev0_.extra_fields AS extra_f11_35_,
	securityev0_.insert_time AS insert_12_35_,
	securityev0_.logs AS logs13_35_,
	securityev0_.NAME AS name14_35_,
	securityev0_.notification AS notific15_35_,
	securityev0_.remarks AS remarks16_35_,
	securityev0_.sensor_id AS sensor_17_35_,
	securityev0_.siem_time AS siem_ti18_35_,
	securityev0_.status AS status19_35_,
	securityev0_.traffic AS traffic20_35_,
	securityev0_.update_time AS update_21_35_ 
FROM
	tb_security_event securityev0_ 
WHERE
	securityev0_.notification @> '{"status":"gdz"}';
ORDER BY
	securityev0_.insert_time DESC 
	LIMIT 5

注意点:

jsonb上的GIN索引支持“@>” “?” “?&” “?|”操作符

2.索引失效场景

当前表有索引，但是表数据为空或者表中只有少量数据不走jsonb字段索引。