openGauss逻辑结构：索引管理

学习目标

掌握openGauss DBMS索引的管理：创建索引、删除索引、查询索引的信息、修改索引的信息。

课程学习

索引是一个指向表中数据的指针。一个数据库中的索引与一本书的索引目录是非常相似的。
索引可以用来提高数据库查询性能，但是不恰当的使用将导致数据库性能下降。

1.创建表，在表中创建索引

--登录omm数据库，创建测试表tabc17，为tabc17的testcol列创建一个索引
[omm@ogdb1 ~]$ gsql -p 40000 -r
gsql ((openGauss 3.1.0 build 4e931f9a) compiled at 2022-09-29 14:19:24 commit 0 last mr  )
Non-SSL connection (SSL connection is recommended when requiring high-security)
Type "help" for help.

omm=# drop table if exists tabc17;
NOTICE:  table "tabc17" does not exist, skipping
DROP TABLE
omm=# create table tabc17(id serial primary key,testcol serial);
NOTICE:  CREATE TABLE will create implicit sequence "tabc17_id_seq" for serial column "tabc17.id"
NOTICE:  CREATE TABLE will create implicit sequence "tabc17_testcol_seq" for serial column "tabc17.testcol"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "tabc17_pkey" for table "tabc17"
CREATE TABLE
omm=# create index idx_tabc17_testcol on tabc17(testcol);
CREATE INDEX
omm=#

--查看索引

omm=# \di
                       List of relations
 Schema |        Name        | Type  | Owner | Table  | Storage
--------+--------------------+-------+-------+--------+---------
 public | idx_tabc17_testcol | index | omm   | tabc17 |
 public | tabc17_pkey        | index | omm   | tabc17 |
(2 rows)

2.通过hint使用索引

--测试准备，创建表customer，并插入数据
omm=# CREATE TABLE customer(ca_address_sk integer NOT NULL ,ca_address_id character(16),ca_street_number character(10) ,ca_street_name character varying(60) ,ca_street_type character(15) ,ca_suite_number character(10) ,ca_city character varying(60) ,ca_county character varying(30) ,ca_state character(2) ,ca_zip character(10) ,ca_country character varying(20) ,ca_gmt_offset numeric(5,2) ,ca_location_type character(20));
CREATE TABLE

omm=# insert into customer values
omm-# (1, 'AAAAAAAABAAAAAAA', '18', 'Jackson', 'Parkway', 'Suite 280', 'Fairfield', 'Maricopa County', 'AZ', '86192' ,'United States', -7.00, 'condo'),
omm-# (2, 'AAAAAAAACAAAAAAA', '362', 'Washington 6th', 'RD', 'Suite 80', 'Fairview', 'Taos County', 'NM', '85709', 'United States', -7.00, 'condo'),
omm-# (3, 'AAAAAAAADAAAAAAA', '585', 'Dogwood Washington', 'Circle', 'Suite Q', 'Pleasant Valley', 'York County', 'PA', '12477', 'United States', -5.00, 'single family');
INSERT 0 3


--创建索引
omm=# create index customer_idx on customer(ca_address_sk);
CREATE INDEX


--通过hint强制使用索引，查看执行计划
omm=# explain select /*+ indexscan(customer customer_idx) */ * from customer where ca_address_sk<100;
                       QUERY PLAN
-------------------------------------------------------------------------------
 [Bypass]
 Index Scan using customer_idx on customer  (cost=0.00..8.27 rows=1 width=280)
   Index Cond: (ca_address_sk < 100)
(3 rows)

omm=#

3.rename索引

omm=# alter index idx_tabc17_testcol rename to idx_tabc17_testcol_new;
ALTER INDEX

4.重建索引

--重建一个单独索引
omm=# alter index idx_tabc17_testcol_new rebuild;
REINDEX
omm=#

omm=# reindex index idx_tabc17_testcol_new ;
REINDEX
omm=#

--重建所有索引

omm=# reindex table tabc17;
REINDEX

5.移动索引到其他表空间

--创建表空间myindex_ts：
omm=#  CREATE TABLESPACE myindex_ts RELATIVE LOCATION 'tablespace/myindex_ts1';
CREATE TABLESPACE

--将索引idx_tabc17_tabc17num_new移动到表空间myindex_ts：
omm=# ALTER INDEX idx_tabc17_testcol_new SET TABLESPACE myindex_ts;
ALTER INDEX

--查看索引所在的表空间
omm=#  select * from pg_indexes where tablename = 'tabc17';
 schemaname | tablename |       indexname        | tablespace |                                         indexdef

------------+-----------+------------------------+------------+------------------------------------------------------------------------
-------------------
 public     | tabc17    | tabc17_pkey            |            | CREATE UNIQUE INDEX tabc17_pkey ON tabc17 USING btree (id) TABLESPACE p
g_default
 public     | tabc17    | idx_tabc17_testcol_new | myindex_ts | CREATE INDEX idx_tabc17_testcol_new ON tabc17 USING btree (testcol) TAB
LESPACE myindex_ts
(2 rows)

--或

omm=#  select * from pg_indexes where indexname = 'idx_tabc17_testcol_new';
 schemaname | tablename |       indexname        | tablespace |                                         indexdef

------------+-----------+------------------------+------------+------------------------------------------------------------------------
-------------------
 public     | tabc17    | idx_tabc17_testcol_new | myindex_ts | CREATE INDEX idx_tabc17_testcol_new ON tabc17 USING btree (testcol) TAB
LESPACE myindex_ts
(1 row)

6.删除索引

--执行下面的命令，删除表tabc17上的索引idx_tabc17_testcol_new：
omm=# drop index idx_tabc17_testcol_new;
DROP INDEX
omm=#
omm=# \di
                     List of relations
 Schema |     Name     | Type  | Owner |  Table   | Storage
--------+--------------+-------+-------+----------+---------
 public | customer_idx | index | omm   | customer |
 public | tabc17_pkey  | index | omm   | tabc17   |
(2 rows)

omm=#