学习目标

学习openGauss收集统计信息、打印执行计划、垃圾收集和checkpoint

课程学习

连接数据库

#第一次进入等待15秒
#数据库启动中...
su - omm
gsql -r

1.准备数据

Create schema tpcds;
CREATE TABLE tpcds.customer_address
(
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)
);
insert into tpcds.customer_address values
(1, 'AAAAAAAABAAAAAAA', '18', 'Jackson', 'Parkway', 'Suite 280', 'Fairfield', 'Maricopa County', 'AZ', '86192' ,'United States', -7.00, 'condo'),
(2, 'AAAAAAAACAAAAAAA', '362', 'Washington 6th', 'RD', 'Suite 80', 'Fairview', 'Taos County', 'NM', '85709', 'United States', -7.00, 'condo'),
(3, 'AAAAAAAADAAAAAAA', '585', 'Dogwood Washington', 'Circle', 'Suite Q', 'Pleasant Valley', 'York County', 'PA', '12477', 'United States', -5.00, 'single family');

–使用序列的generate_series(1,N)函数对表插入数据

insert into tpcds.customer_address values(generate_series(10, 10000));

2.收集统计信息

–查看系统表中表的统计信息

select relname, relpages, reltuples from pg_class where relname = 'customer_address';

—使用ANALYZE VERBOSE语句更新统计信息，并输出表的相关信息

analyze VERBOSE tpcds.customer_address;

–查看系统表中表的统计信息

select relname, relpages, reltuples from pg_class where relname = 'customer_address';

3.打印执行计划

–使用默认的打印格式

SET explain_perf_mode=normal;

–显示表简单查询的执行计划

EXPLAIN SELECT * FROM tpcds.customer_address;

–以JSON格式输出的执行计划（explain_perf_mode为normal时）

EXPLAIN(FORMAT JSON) SELECT * FROM tpcds.customer_address;

–禁止开销估计的执行计划

EXPLAIN(COSTS FALSE)SELECT * FROM tpcds.customer_address;

–带有聚集函数查询的执行计划

EXPLAIN SELECT SUM(ca_address_sk) FROM tpcds.customer_address WHERE ca_address_sk<100;

–有索引条件的执行计划

create index customer_address_idx on tpcds.customer_address(ca_address_sk);
EXPLAIN SELECT * FROM tpcds.customer_address WHERE ca_address_sk<100;

4.垃圾收集

–VACUUM回收表或B-Tree索引中已经删除的行所占据的存储空间

update tpcds.customer_address set ca_address_sk = ca_address_sk + 1 where ca_address_sk <100;
VACUUM (VERBOSE, ANALYZE) tpcds.customer_address;

5.事务日志检查点

–检查点（CHECKPOINT）是一个事务日志中的点，所有数据文件都在该点被更新以反映日志中的信息，所有数据文件都将被刷新到磁盘

CHECKPOINT;

6.清理数据

drop schema tpcds cascade;

课后作业

1.创建分区表，并用generate_series(1,N)函数对表插入数据

create table test(a int,b varchar(20));
insert into test values(generate_series(1,10000));

2.收集表统计信息

select relname, relpages, reltuples from pg_class where relname = 'test';
analyze VERBOSE test;
select relname, relpages, reltuples from pg_class where relname = 'test';

3.显示简单查询的执行计划；建立索引并显示有索引条件的执行计划

set explain_perf_mode=normal;
explain select * from test;

create index test_index on test(a);
explain select * from test where a<1000;

4.更新表数据，并做垃圾收集

update test set b = b+1 where a<1000;
vacuum (verbose,analyse) test;

5.清理数据

drop table test;