| 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
288 redo size
677 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
结论：对于新创建的表来说，因为创建的是空表就没有对表里的空间进行分配，当插入第一条数据时，就需要对区上的块进行空间分配和对数据字典的一些操作，就会有比较大的db_block_size。如果再次插入数据的话就基本没有对空间的分配啥的，就会有比较少的db_block_size产生。
所以对于extent指定的区大小来说 同样的空表插入同样的数据 db_block_size 可能不同。
对插入更新、删除的实验：SYS@ORCL>update test_db1 set x=3 where x=1;
1 row updated.
Execution Plan
----------------------------------------------------------
Plan hash value: 2185639234
-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------
| 0 | UPDATE STATEMENT | | 1 | 13 | 2 (0)| 00:00:01 |
| 1 | UPDATE | TEST_DB1 | | | | |
|* 2 | TABLE ACCESS FULL| TEST_DB1 | 1 | 13 | 2 (0)| 00:00:01 |
-------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("X"=1)
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
28 recursive calls
1 db block gets
11 consistent gets
0 physical reads
388 redo size
678 bytes sent via SQL*Net to client
565 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>delete test_db1 where x=2;
1 row deleted.
Execution Plan
----------------------------------------------------------
Plan hash value: 3135214910
-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------
| 0 | DELETE STATEMENT | | 1 | 13 | 2 (0)| 00:00:01 |
| 1 | DELETE | TEST_DB1 | | | | |
|* 2 | TABLE ACCESS FULL| TEST_DB1 | 1 | 13 | 2 (0)| 00:00:01 |
-------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("X"=2)
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
5 recursive calls
1 db block gets
9 consistent gets
0 physical reads
288 redo size
678 bytes sent via SQL*Net to client
557 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(&x);
Enter value for x: 1
old 1: insert into test_db1 values(&x)
new 1: insert into test_db1 values(1)
1 row created.
。。。。
SYS@ORCL>commit;
Commit complete.
SYS@ORCL>select * from test_db1;
X