关于db_block_size的理解和实验 - 数据库编程

关于对db_block_gets的理解与实验

实验

一、自己手动创建的小表

创建一个区大小为 40k
SYS@ORCL>show parameter db_block_size

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_block_size integer 8192

SYS@ORCL>create tablespace tyger1 datafile '/u01/app/oracle/oradata/ORCL/tyger1.dbf' size 10m
2 extent management local uniform size 40k;

Tablespace created.

SYS@ORCL>create table test_db1(x int) tablespace tyger1;

Table created.

SYS@ORCL>set autotrace on
SYS@ORCL>insert into test_db1 values(1);

1 row created.

Execution Plan
----------------------------------------------------------
-------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------
| 0 | INSERT STATEMENT | | 1 | 100 | 1 (0)| 00:00:01 |
-------------------------------------------------------------------------
Statistics
----------------------------------------------------------
1 recursive calls
19 db block gets
1 consistent gets
3 physical reads
964 redo size
675 bytes sent via SQL*Net to client
562 bytes received via SQL*Net from client
4 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
1 rows processed

SYS@ORCL>insert into test_db1 values(2);

1 row created.

Execution Plan
----------------------------------------------------------

-------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------
| 0 | INSERT STATEMENT | | 1 | 100 | 1 (0)| 00:00:01 |
-------------------------------------------------------------------------

Statistics
----------------------------------------------------------

1 recursive calls
3 db block gets
1 consistent gets
0 physical reads
244 redo size
675 bytes sent via SQL*Net to client
562 bytes received via SQL*Net from client
4 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
1 rows processed

2. 创建一个区大小为80k
SYS@ORCL>create tablespace tyger2 datafile '/u01/app/oracle/oradata/ORCL/tyger2.dbf' size 10m
2 extent management local uniform size 80k;

Tablespace created.

SYS@ORCL>create table test_db2(x int) tablespace tyger2;

Table created.

SYS@ORCL>insert into test_db2 values(1);

1 row created.

Execution Plan
----------------------------------------------------------

-------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------
| 0 | INSERT STATEMENT | | 1 | 100 | 1 (0)| 00:00:01 |
-------------------------------------------------------------------------

Statistics
----------------------------------------------------------
1 recursive calls
29 db block gets
1 consistent gets
28 physical reads
1364 redo size
675 bytes sent via SQL*Net to client
562 bytes received via SQL*Net from client
4 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
1 rows processed

SYS@ORCL>insert into test_db2 values(2);

1 row created.

Execution Plan
----------------------------------------------------------

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关于db_block_size的理解和实验(一)