openGauss每日一练第19天 | 学习心得体会

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

omm=# create table tom
(
        id int,
        c2 CHAR(2)
)
partition by range (id)
(
        partition tom_p0 values less than (1000),
        partition tom_p1 values less than (2000),
        partition tom_p2 values less than (3000),
          omm-#   partition tom_p3 values less than (4000),
            partition tom_p4 values less than (500000)
); 
CREATE TABLE


omm=# insert into tom  values(generate_series(10, 100000));       
INSERT 0 99991

2.收集表统计信息

omm=# select relname, relpages, reltuples from pg_class where relname = 'tom';
 relname | relpages | reltuples 
---------+----------+-----------
 tom     |        0 |         0
(1 row)

omm=# analyze VERBOSE tom;
INFO:  analyzing "public.tom"(gaussdb pid=1)
INFO:  ANALYZE INFO : "tom": scanned 5 of 5 pages, containing 990 live rows and 0 dead rows; 338 rows in sample, 990 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "tom": scanned 5 of 5 pages, containing 1000 live rows and 0 dead rows; 338 rows in sample, 1000 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "tom": scanned 5 of 5 pages, containing 1000 live rows and 0 dead rows; 338 rows in sample, 1000 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "tom": scanned 5 of 5 pages, containing 1000 live rows and 0 dead rows; 338 rows in sample, 1000 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "tom": scanned 425 of 425 pages, containing 96001 live rows and 0 dead rows; 28648 rows in sample, 96001 estimated total rows(gaussdb pid=1)
ANALYZE
omm=# select relname, relpages, reltuples from pg_class where relname = 'tom';
 relname | relpages | reltuples 
---------+----------+-----------
 tom     |      445 |     99991
(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=# explain select * from tom where id=1000;
                               QUERY PLAN                                
-------------------------------------------------------------------------
 Partition Iterator  (cost=0.00..1338.89 rows=1 width=16)
   Iterations: 1
   ->  Partitioned Seq Scan on tom  (cost=0.00..1338.89 rows=1 width=16)
         Filter: (id = 1000)
         Selected Partitions:  2
(5 rows)
omm=# create index inx_id on tom(id);
CREATE INDEX
omm=# explain select * from tom where id=1000;
                            QUERY PLAN                             
-------------------------------------------------------------------
 Index Scan using inx_id on tom  (cost=0.00..8.27 rows=1 width=16)
   Index Cond: (id = 1000)
(2 rows)

4.更新表数据，并做垃圾收集

omm=# update tom set id=id+200 ;
UPDATE 99991
omm=# vacuum (verbose,analyze) tom;
INFO:  vacuuming "public.tom"(gaussdb pid=1)
INFO:  index "inx_id" now contains 1780 row versions in 827 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:  "tom": found 0 removable, 1780 nonremovable row versions in 8 out of 8 pages(gaussdb pid=1)
DETAIL:  990 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 "public.tom"(gaussdb pid=1)
INFO:  index "inx_id" now contains 2000 row versions in 827 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:  "tom": found 0 removable, 2000 nonremovable row versions in 9 out of 9 pages(gaussdb pid=1)
DETAIL:  1000 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 "public.tom"(gaussdb pid=1)
INFO:  index "inx_id" now contains 2000 row versions in 827 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:  "tom": found 0 removable, 2000 nonremovable row versions in 9 out of 9 pages(gaussdb pid=1)
DETAIL:  1000 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 "public.tom"(gaussdb pid=1)
INFO:  index "inx_id" now contains 2000 row versions in 827 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:  "tom": found 0 removable, 2000 nonremovable row versions in 9 out of 9 pages(gaussdb pid=1)
DETAIL:  1000 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 "public.tom"(gaussdb pid=1)
INFO:  index "inx_id" now contains 192202 row versions in 827 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:  "tom": found 0 removable, 192202 nonremovable row versions in 851 out of 851 pages(gaussdb pid=1)
DETAIL:  96001 dead row versions cannot be removed yet.
There were 0 unused item pointers.
0 pages are entirely empty.
CPU 0.00s/0.02u sec elapsed 0.03 sec.
INFO:  scanned index "inx_id" to remove 0.000000 invisible rows(gaussdb pid=1)
DETAIL:  CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  analyzing "public.tom"(gaussdb pid=1)
INFO:  ANALYZE INFO : "tom": scanned 8 of 8 pages, containing 790 live rows and 990 dead rows; 271 rows in sample, 790 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "tom": scanned 9 of 9 pages, containing 1000 live rows and 1000 dead rows; 305 rows in sample, 1000 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "tom": scanned 9 of 9 pages, containing 1000 live rows and 1000 dead rows; 305 rows in sample, 1000 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "tom": scanned 9 of 9 pages, containing 1000 live rows and 1000 dead rows; 305 rows in sample, 1000 estimated total rows(gaussdb pid=1)
INFO:  ANALYZE INFO : "tom": scanned 851 of 851 pages, containing 96201 live rows and 96001 dead rows; 28814 rows in sample, 96201 estimated total rows(gaussdb pid=1)
VACUUM

5.清理数据
omm=# drop table tom;
DROP TABLE