PostgreSQL json 索引實踐 - 檢索(存在、包含、等值、範圍等)加速

JSON PostgreSQL · 發表 2018-10-05 17:56:13

摘要：標籤 PostgreSQL , json , gin , rum 背景使用者在使用JSON型別時，常見的一些JSON搜尋包括： 1、存在，JSON中是否存在某個KEY，某些KEY，某些KEY的任意一個存在某個KEY(TOP LEVEL) '{"...

背景

使用者在使用JSON型別時，常見的一些JSON搜尋包括：

1、存在，JSON中是否存在某個KEY，某些KEY，某些KEY的任意一個

存在某個KEY(TOP LEVEL)

'{"a":1, "b":2}'::jsonb ? 'b'

存在所有KEY

'{"a":1, "b":2, "c":3}'::jsonb ?& array['b', 'c']

存在任意KEY、元素

'["a", "b"]'::jsonb ?| array['a', 'b']

2、等值，JSON中是否存在指定的key:value對（支援巢狀JSON）

'{"a":1, "b":2}'::jsonb @> '{"b":2}'::jsonb

3、包含，JSON中某個路徑下的VALUE（陣列）中，是否包含指定的所有元素。

postgres=# select jsonb '{"a":1, "b": {"c":[1,2,3], "d":["k","y","z"]}, "d":"kbc"}' @> '{"b":{"c":[2,3]}}';
 ?column?
----------
 t
(1 row)

4、相交，JSON中某個路徑下的VALUE（陣列）中，是否包含指定的任意元素。

postgres=# select jsonb '{"a":1, "b": {"c":[1,2,3], "d":["k","y","z"]}, "d":"kbc"}' @> '{"b":{"c":[2]}}'
or
jsonb '{"a":1, "b": {"c":[1,2,3], "d":["k","y","z"]}, "d":"kbc"}' @> '{"b":{"c":[3]}}'
;

 ?column?
----------
 t
(1 row)

或(注意1,2,3需要雙引號，作為text型別儲存，因為操作符?| ?& 暫時只支援了text[]，如果是numeric匹配不上)

postgres=# select jsonb '{"a":1, "b": {"c":["1","2","3"], "d":["k","y","z"]}, "d":"kbc"}' -> 'b' -> 'c' ?& array['2','3','4'] ;
 ?column?
----------
 f
(1 row)

postgres=# select jsonb '{"a":1, "b": {"c":["1","2","3"], "d":["k","y","z"]}, "d":"kbc"}' -> 'b' -> 'c' ?| array['2','3','4'] ;
 ?column?
----------
 t
(1 row)

5、範圍查詢，JSON中某個路徑下的VALUE，是否落在某個範圍內。

(js ->> 'key1' )::numeric between xx and xx

(js ->> 'key2' )::numeric between xx and xx

這些操作如何加速，或者如何使用索引加速？

一、json 索引支援

GIN的兩個OPS，分別支援JSON：

The default GIN operator class for jsonb supports queries with top-level key-exists operators ?, ?& and ?| operators and path/value-exists operator @>.

The non-default GIN operator class jsonb_path_ops supports indexing the @> operator only.

1、支援 `@>` 操作符的索引如下（jsonb_path_ops只支援`@>` 操作符，但是效率高）

postgres=# create table tbl(id int, js jsonb);
CREATE TABLE
postgres=# create index idx_tbl_1 on tbl using gin (js jsonb_path_ops);
CREATE INDEX

2、支援除範圍查詢以外的所有查詢的索引如下

postgres=# create table tbl(id int, js jsonb);
CREATE TABLE
postgres=# create index idx_tbl_1 on tbl using gin (js);-- 使用預設ops即可
CREATE INDEX

二、JSON KEY VALUE值範圍查詢加速

某些使用，需要對VALUE使用範圍查詢，比如時間(如果要建索引，請使用numeric表示，否則需要自定義immutable函式)，數值都有這些需求。

通常的做法，把範圍查詢的型別提取出來，建立btree表示式索引，如果有任意組合的範圍查詢，使用gin或rum表示式索引。

例子

create index idx1 on tbl ( ((js->>'k1')::float8) );
create index idx2 on tbl ( ((js->>'k2')::numeric) );
...
create index idxn on tbl ( ((js->>'kn')::float8) );

或

create extension btree_gin;
create index idx1 on tbl using gin( ((js->>'k1')::float8), ((js->>'k2')::numeric), ... ((js->>'kn')::float8) );

或

create extension rum;
create index idx1 on tbl using rum( ((js->>'k1')::float8), ((js->>'k2')::numeric), ... ((js->>'kn')::float8) );

或

create or replace function to_timestamp(text) returns timestamp as $$
select $1::timestamp;
$$ language sql strict immutable;


create index idx1 on tbl using gin( ((js->>'k1')::float8), to_timestamp(js->>'k2'), ... ((js->>'kn')::float8) );
或
create index idx1 on tbl using rum( ((js->>'k1')::float8), to_timestamp(js->>'k2'), ... ((js->>'kn')::float8) );

三、索引使用例子

create table tbl(id int, js jsonb);
create index idx_tbl_1 on tbl using gin (js jsonb_path_ops);
create index idx_tbl_2 on tbl using gin (js);
create index idx_tbl_3 on tbl using rum( ((js->>'k1')::float8), to_timestamp(js->>'k2'), ((js->>'k3')::numeric) );

postgres=# explain select * from tbl where js ? 'a';
QUERY PLAN
------------------------------------------------------------------------
 Bitmap Heap Scan on tbl(cost=2.21..3.32 rows=1 width=36)
Recheck Cond: (js ? 'a'::text)
->Bitmap Index Scan on idx_tbl_2(cost=0.00..2.21 rows=1 width=0)
Index Cond: (js ? 'a'::text)
(4 rows)

postgres=# explain select * from tbl where js @> '{"a":"b"}';
QUERY PLAN
------------------------------------------------------------------------
 Bitmap Heap Scan on tbl(cost=2.21..3.32 rows=1 width=36)
Recheck Cond: (js @> '{"a": "b"}'::jsonb)
->Bitmap Index Scan on idx_tbl_1(cost=0.00..2.21 rows=1 width=0)
Index Cond: (js @> '{"a": "b"}'::jsonb)
(4 rows)

postgres=# explain select * from tbl where to_timestamp(js->>'k2') between '2018-01-01' and '2018-01-02';
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Index Scan using idx_tbl_3 on tbl(cost=5.50..12.22 rows=6 width=36)
Index Cond: ((to_timestamp((js ->> 'k2'::text)) >= '2018-01-01 00:00:00'::timestamp without time zone) AND (to_timestamp((js ->> 'k2'::text)) <= '2018-01-02 00:00:00'::timestamp without time zone))
(2 rows)

postgres=# explain select * from tbl where to_timestamp(js->>'k2') between '2018-01-01' and '2018-01-02' and ((js->>'k3')::numeric) between 1 and 200;
QUERY PLAN

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------
 Index Scan using idx_tbl_3 on tbl(cost=9.90..12.11 rows=1 width=36)
Index Cond: ((to_timestamp((js ->> 'k2'::text)) >= '2018-01-01 00:00:00'::timestamp without time zone) AND (to_timestamp((js ->> 'k2'::text)) <= '2018-01-02 00:00:00'::timestamp without time zone) AND (((js ->> 'k3'::text))::numeric >
= '1'::numeric) AND (((js ->> 'k3'::text))::numeric <= '200'::numeric))
(2 rows)


postgres=# select * from tbl where js @> '{"a": {"b":"c"}}';
 id | js
----+----
(0 rows)

SELECT doc->'site_name' FROM websites
WHERE doc->'tags' @> '[{"term":"paris"}, {"term":"food"}]';

postgres=# select jsonb '{"a":1, "b": {"c":[1,2,3], "d":["k","y","z"]}, "d":"kbc"}';
jsonb
-------------------------------------------------------------------
 {"a": 1, "b": {"c": [1, 2, 3], "d": ["k", "y", "z"]}, "d": "kbc"}
(1 row)

postgres=# select jsonb '{"a":1, "b": {"c":[1,2,3], "d":["k","y","z"]}, "d":"kbc"}' @> '{"b":{"c":[2,3]}}';
 ?column?
----------
 t
(1 row)

postgres=# select jsonb '{"a":1, "b": {"c":[1,2,3], "d":["k","y","z"]}, "d":"kbc"}' @> '{"b":{"c":[2,4]}}';
 ?column?
----------
 f
(1 row)


postgres=# explain select * from tbl where js @> '{"b":{"c":[2,4]}}';
QUERY PLAN
------------------------------------------------------------------------
 Bitmap Heap Scan on tbl(cost=3.31..4.42 rows=1 width=36)
Recheck Cond: (js @> '{"b": {"c": [2, 4]}}'::jsonb)
->Bitmap Index Scan on idx_tbl_1(cost=0.00..3.31 rows=1 width=0)
Index Cond: (js @> '{"b": {"c": [2, 4]}}'::jsonb)
(4 rows)