gin索引字段entry构造的TREE，在末端posting tree|list 里面存储的是entry对应的行号. 别无其他信息。rum索引，与GIN类似，但是在posting list|tree的每一个ctid(itempoint)后面会追加一些属性值。因此，有些场景，使用rum 索引，性能会优很多。以下举个例子比较下。

Note: KingbaseES v8r6c5b0023 版本，附带了rum插件。 

1、构造数据

create table t1 as select name,short_desc from pg_settings;
alter table t1 add column tsv tsvector;
update t1 set tsv=to_tsvector(short_desc);

--number for 紧邻的只有一条
test=# select short_desc from t1 where to_tsvector(short_desc) @@ to_tsquery('number <-> for');
       short_desc        
-------------------------
 Top SQL number for kddm
(1 row)

--同时包含number and for 的有7条
test=# select short_desc from t1 where to_tsvector(short_desc) @@ to_tsquery('number') and to_tsvector(short_desc) @@ to_tsquery('for');
                                  short_desc                                   
-------------------------------------------------------------------------------
 Sets the number of digits displayed for floating-point values.
 Sets the maximum number of simultaneously open files for each server process.
 Sets the number of connection slots reserved for superusers.
 Top SQL number for kddm
 Sets the number of disk-page buffers in shared memory for WAL.
 Sets the number of WAL files held for standby servers.
 Sets the number of locks used for concurrent xlog insertions.
(7 rows)

2、gin 索引

创建gin 索引：

create index ind_t1_gin on t1 using gin(tsv);

查看gin索引执行计划：通过索引返回7条记录，也就是索引没有包含位置的信息，需要访问表数据。

test=# explain analyze select short_desc from t1 where tsv @@ to_tsquery('number <-> for');                    
                                                     QUERY PLAN                                                     
--------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on t1  (cost=12.32..30.68 rows=9 width=55) (actual time=0.111..0.195 rows=1 loops=1)
   Recheck Cond: (tsv @@ to_tsquery('number <-> for'::text))
   Rows Removed by Index Recheck: 6
   Heap Blocks: exact=4
   ->  Bitmap Index Scan on ind_t1_gin  (cost=0.00..12.32 rows=9 width=0) (actual time=0.058..0.058 rows=7 loops=1)
         Index Cond: (tsv @@ to_tsquery('number <-> for'::text))
 Planning Time: 0.199 ms
 Execution Time: 0.227 ms
(8 rows)

3、rum 索引

 创建索引：

test=# create extension rum;
CREATE EXTENSION
test=# create index ind_t1_rum on t1 using rum(tsv);       
CREATE INDEX

查看执行计划：可以看到索引返回的记录就一条，也就是索引包含有位置信息。

test=# explain analyze select short_desc from t1 where tsv @@ to_tsquery('number <-> for'); 
                                                     QUERY PLAN                                                     
--------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on t1  (cost=12.32..30.68 rows=9 width=55) (actual time=0.041..0.042 rows=1 loops=1)
   Recheck Cond: (tsv @@ to_tsquery('number <-> for'::text))
   Heap Blocks: exact=1
   ->  Bitmap Index Scan on ind_t1_rum  (cost=0.00..12.32 rows=9 width=0) (actual time=0.038..0.039 rows=1 loops=1)
         Index Cond: (tsv @@ to_tsquery('number <-> for'::text))
 Planning Time: 0.297 ms
 Execution Time: 0.068 ms
(7 rows)