openGauss每日一练第19天 课程笔记和作业

数据库环境

openGauss:2.0.0 - 数据库实训平台

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

学习笔记

• 查看系统表中表的统计信息

omm=# analyze VERBOSE tpcds.customer_address;
INFO:  analyzing "tpcds.customer_address"(gaussdb pid=1)
INFO:  ANALYZE INFO : "customer_address": scanned 55 of 55 pages, containing 9994 live rows and 0 dead rows; 9994 rows in sample, 9994 estimated total rows(gaussdb pid=1)
ANALYZE
omm=# select relname, relpages, reltuples from pg_class where relname = 'customer_address';
     relname      | relpages | reltuples 
------------------+----------+-----------
 customer_address |       55 |      9994
(1 row)

• explain_perf_mode为normal时, 以JSON格式输出的执行计划

SET explain_perf_mode=normal;
EXPLAIN(FORMAT JSON) SELECT * FROM tpcds.customer_address;

课后作业

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

omm=# create schema my_schema;
CREATE SCHEMA

omm=# create table my_schema.product
omm-# (
omm(#     product_id integer,
omm(#     product_name char(30)
omm(# )
omm-# partition by range(product_id)
omm-# (
omm(#     partition p0 values less than (500),
omm(#     partition p1 values less than (1000),
omm(#     partition p2 values less than (2000),
omm(#     partition p3 values less than (maxvalue)
omm(# );
CREATE TABLE

omm=# insert into my_schema.product values(generate_series(1,10000));
INSERT 0 10000

omm=# select * from my_schema.product limit 10;
 product_id | product_name 
------------+--------------
          1 | 
          2 | 
          3 | 
          4 | 
          5 | 
          6 | 
          7 | 
          8 | 
          9 | 
         10 | 
(10 rows)

2.收集表统计信息

omm=# analyze VERBOSE my_schema.product;     
INFO:  analyzing "my_schema.product"(gaussdb pid=1)
INFO:  ANALYZE INFO : "product": scanned 3 of 3 pages, containing 499 live rows and 0 dead rows; 499 rows in sample, 499 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "product": scanned 3 of 3 pages, containing 500 live rows and 0 dead rows; 500 rows in sample, 500 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "product": scanned 5 of 5 pages, containing 1000 live rows and 0 dead rows; 1000 rows in sample, 1000 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "product": scanned 36 of 36 pages, containing 8001 live rows and 0 dead rows; 8001 rows in sample, 8001 estimated total rows(gaussdb pid=1)
ANALYZE
omm=# select relname, relpages, reltuples from pg_class where relname = 'product';
 relname | relpages | reltuples 
---------+----------+-----------
 product |       47 |     10000
(1 row)

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

omm=# SET explain_perf_mode=normal;
SET
omm=# explain select * from my_schema.product;
                                   QUERY PLAN                                    
---------------------------------------------------------------------------------
omm=#  Partition Iterator  (cost=0.00..147.00 rows=10000 width=128)
   Iterations: 4
   ->  Partitioned Seq Scan on product  (cost=0.00..147.00 rows=10000 width=128)
         Selected Partitions:  1..4
(4 rows)

omm=# create index product_id_index on my_schema.product(product_id);
CREATE INDEX

omm=# explain select * from my_schema.product where product_id > 5000;
                                      QUERY PLAN                                       
---------------------------------------------------------------------------------------
 Index Scan using product_id_index on product  (cost=0.00..112.75 rows=5000 width=128)
   Index Cond: (product_id > 5000)
(2 rows)

4.更新表数据，并做垃圾收集

omm=# update my_schema.product set product_id = product_id - 100 where product_id > 3000;
UPDATE 7000
omm=# VACUUM (VERBOSE, ANALYZE) my_schema.product;
INFO:  vacuuming "my_schema.product"(gaussdb pid=1)

DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "product_id_index" now contains 499 row versions in 68 pages(gaussdb pid=1)
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "product": found 0 removable, 499 nonremovable row versions in 3 out of 3 pages(gaussdb pid=1)INFO:  vacuuming "my_schema.product"(gaussdb pid=1)
INFO:  index "product_id_index" now contains 500 row versions in 68 pages(gaussdb pid=1)
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "product": found 0 removable, 500 nonremovable row versions in 3 out of 3 pages(gaussdb pid=1)
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  vacuuming "my_schema.product"(gaussdb pid=1)
INFO:  index "product_id_index" now contains 1000 row versions in 68 pages(gaussdb pid=1)
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "product": found 0 removable, 1000 nonremovable row versions in 5 out of 5 pages(gaussdb pid=1)
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  vacuuming "my_schema.product"(gaussdb pid=1)
INFO:  index "product_id_index" now contains 15001 row versions in 68 pages(gaussdb pid=1)
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "product": found 0 removable, 15001 nonremovable row versions in 67 out of 67 pages(gaussdb pid=1)
DETAIL:  7000 dead row versions cannot be removed yet.
There were 0 unused item pointers.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  scanned index "product_id_index" to remove 0.000000 invisible rows(gaussdb pid=1)
DETAIL:  CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  analyzing "my_schema.product"(gaussdb pid=1)
INFO:  ANALYZE INFO : "product": scanned 3 of 3 pages, containing 499 live rows and 0 dead rows; 499 rows in sample, 499 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "product": scanned 3 of 3 pages, containing 500 live rows and 0 dead rows; 500 rows in sample, 500 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "product": scanned 5 of 5 pages, containing 1000 live rows and 0 dead rows; 1000 rows in sample, 1000 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "product": scanned 67 of 67 pages, containing 8001 live rows and 7000 dead rows; 8001 rows in sample, 8001 estimated total rows(gaussdb pid=1)
VACUUM
omm=# CHECKPOINT;
CHECKPOINT

5.清理数据

omm=# drop schema my_schema cascade;
NOTICE:  drop cascades to table my_schema.product
DROP SCHEMA

学习资源

• openGauss SQL学习参考资料
• 每日一练：openGauss数据库在线实训课程
• openGauss每日一练 | 21期养成好习惯，提升技术能力！
• 墨天轮Markdown编辑器使用介绍
• 墨天轮数据库在线实训平台V1.0操作手册
• 墨天轮数据社区

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