blocks

1.查看一个表空间，有多少个extents，多少blocks，多少空余空间。

select a.tablespace_name, sumblocks, nvl(usedextents, 0) usedextents, 
           nvl(usedblocks, 0) usedblocks, freeblocks, 
           nvl(usedblocks,0) + nvl(freeblocks,0)checkblocks, 
           sumblocks-nvl(usedblocks, 0)-nvl(freeblocks,0) minblocks
from (select tablespace_name, sum(blocks) sumblocks from dba_data_files 
             group by tablespace_name ) A, 
           (select tablespace_name, sum(extents) usedextents, sum(blocks) usedblocks from dba_segments
            group by tablespace_name ) B, 
          (select tablespace_name, sum(blocks) freeblocks from dba_free_space
           group by tablespace_name ) C  
where a.tablespace_name=b.tablespace_name(+)
 12       and a.tablespace_name=c.tablespace_name(+);

 

TABLESPACE_NAME         SUMBLOCKS USEDEXTENTS USEDBLOCKS FREEBLOCKS CHECKBLOCKS  MINBLOCKS

------------------------------ ---------- ----------- ---------- ---------- ----------- ----------

SYSAUX                    67840     5128       63576       4136      67712        128

UNDOTBS1                11520       36        2208       9184      11392        128

USERS                      960       89         712    168        880     80

SYSTEM                    90880     3042       89648       1104      90752        128

EXAMPLE                 12800      884        9952       2720      12672        128

UNOTBS_NEW                12800      162        4536       8136      12672        128

 

6 rows selected.

 

SQL>

2.示例演示通过rowid得到数据块的相关信息（所在对象，文件，数据块）。

SQL> create table tt as select * from dba_objects where object_id < 10;

 

Table created.

SQL> select rowid,object_id,object_name from tt;

 

ROWID            OBJECT_ID OBJECT_NAME

------------------ ---------- --------------------------------------------------------------------------------------------------------------------------------

AAASVGAABAAAVUZAAA        2 C_OBJ#

AAASVGAABAAAVUZAAB        3 I_OBJ#

AAASVGAABAAAVUZAAC        4 TAB$

AAASVGAABAAAVUZAAD        5 CLU$

AAASVGAABAAAVUZAAE        6 C_TS#

AAASVGAABAAAVUZAAF        7 I_TS#

AAASVGAABAAAVUZAAG        8 C_FILE#_BLOCK#

AAASVGAABAAAVUZAAH        9 I_FILE#_BLOCK#

 

8 rows selected.

select
rowid,dbms_rowid.rowid_object(rowid) object_id,
dbms_rowid.rowid_relative_fno(rowid) file_id,
dbms_rowid.rowid_block_number(rowid) block_id,
dbms_rowid.rowid_row_number(rowid) row_id
  6  from tt;

 

ROWID            OBJECT_ID     FILE_ID   BLOCK_ID    ROW_ID

------------------ ---------- ---------- ---------- ----------

AAASVGAABAAAVUZAAA    75078           1      87321         0

AAASVGAABAAAVUZAAB    75078           1      87321         1

AAASVGAABAAAVUZAAC    75078           1      87321         2

AAASVGAABAAAVUZAAD    75078           1      87321         3

AAASVGAABAAAVUZAAE    75078           1      87321         4

AAASVGAABAAAVUZAAF    75078           1      87321         5

AAASVGAABAAAVUZAAG    75078           1      87321         6

AAASVGAABAAAVUZAAH    75078           1      87321         7

 

8 rows selected.

 

SQL> select object_name from dba_objects where object_id=75078;

 

OBJECT_NAME

--------------------------------------------------------------------------------------------------------------------------------

TT

 

SQL>

3.示例说明consistent read,current read,logical read,phicical read的概念及关系。

SQL> set autotrace traceonly stat
SQL> alter system flush buffer_cache;

System altered.

 

SQL> alter system flush buffer_cache;

 

System altered.

 

SQL> select * from dba_objects;

 

72552 rows selected.

 

 

Statistics

----------------------------------------------------------

     15  recursive calls

      0  db block gets

       7719  consistent gets

       1469  physical reads

      0  redo size

    3472080  bytes sent via SQL*Net to client

      53616  bytes received via SQL*Net from client

       4838  SQL*Net roundtrips to/from client

      0  sorts (memory)

      0  sorts (disk)

      72552  rows processed

 

SQL> select * from dba_objects;

 

72552 rows selected.

 

 

Statistics

----------------------------------------------------------

      0  recursive calls

      0  db block gets

       7715  consistent gets

      0  physical reads

      0  redo size

    3472080  bytes sent via SQL*Net to client

      53616  bytes received via SQL*Net from client

       4838  SQL*Net roundtrips to/from client

      0  sorts (memory)

      0  sorts (disk)

      72552  rows processed

 

SQL>

逻辑读：current read又叫做db block gets，逻辑读=db block gets+consistent read

物理读：从磁盘中读到内存中

4.设计一个例子，演示PCTUSED和PCTFREE对数据操作的影响。

SQL> drop table tt purge;

 

Table dropped.

 

SQL> create table tt as select * from sys_objects where rownum < 500;

 

Table created.

 

SQL>  select pct_free,pct_used,blocks,num_rows,avg_row_len from dba_tables where table_name='TT';

 

  PCT_FREE   PCT_USED      BLOCKS   NUM_ROWS AVG_ROW_LEN

---------- ---------- ---------- ---------- -----------

    10       40

 

SQL>  analyze table TT compute statistics;

 

Table analyzed.

 

SQL>  select pct_free,pct_used,blocks,num_rows,avg_row_len from dba_tables where table_name='TT';

 

  PCT_FREE   PCT_USED      BLOCKS   NUM_ROWS AVG_ROW_LEN

---------- ---------- ---------- ---------- -----------

    10       40           3    499         28

 

 

SQL>  select pct_free,pct_used,blocks,num_rows,avg_row_len from dba_tables where table_name='TT';

 

  PCT_FREE   PCT_USED      BLOCKS   NUM_ROWS AVG_ROW_LEN

---------- ---------- ---------- ---------- -----------

    10       40           3    499         28

 

SQL> INSERT INTO TT select * from TT where rownum<21;

 

20 rows created.

 

SQL> commit;

 

Commit complete.

 

SQL>  analyze table TT compute statistics;

 

Table analyzed.

SQL>  select pct_free,pct_used,blocks,num_rows,avg_row_len from dba_tables where table_name='TT';

 

  PCT_FREE   PCT_USED      BLOCKS   NUM_ROWS AVG_ROW_LEN

---------- ---------- ---------- ---------- -----------

    10       40           4    520         28

 

SQL> CREATE TABLESPACE USER03 DATAFILE 'USER03' SIZE 100M AUTOEXTEND ON NEXT 10M MAXSIZE UNLIMITED SEGMENT SPACE MANAGEMENT manual;

Tablespace created.

 

SQL> create table t03 tablespace USER03 as  select * from dba_objects where rownum<500;

 

Table created.

 

SQL>  select pct_free,pct_used,blocks,num_rows,avg_row_len from dba_tables where table_name='T03';

 

  PCT_FREE   PCT_USED      BLOCKS   NUM_ROWS AVG_ROW_LEN

---------- ---------- ---------- ---------- -----------

    10       40

 

SQL>  analyze table T03 compute statistics;

 

Table analyzed.

 

SQL>  select pct_free,pct_used,blocks,num_rows,avg_row_len from dba_tables where table_name='T03';

 

  PCT_FREE   PCT_USED      BLOCKS   NUM_ROWS AVG_ROW_LEN

---------- ---------- ---------- ---------- -----------

    10       40           7    499         87

 

SQL> INSERT INTO T03 select * from T03 where rownum<81;

 

80 rows created.

SQL> commit;

 

Commit complete.

SQL>  analyze table T03 compute statistics;

 

Table analyzed.

 

SQL>  select pct_free,pct_used,blocks,num_rows,avg_row_len from dba_tables where table_name='T03';

 

  PCT_FREE   PCT_USED      BLOCKS   NUM_ROWS AVG_ROW_LEN

---------- ---------- ---------- ---------- -----------

    10       40           7    369         89

 

5.设计一个例子，演示数据块整理（合并）的效果。

 

SQL> create table t as select object_id,object_name from dba_objects;

Table created.

 

SQL> insert into  t select object_id,object_name from dba_objects;

72552 rows created.

 

SQL> insert into  t select object_id,object_name from dba_objects;

72552 rows created.

 

SQL> insert into  t select object_id,object_name from dba_objects;

72552 rows created.

 

SQL> insert into  t select object_id,object_name from dba_objects;

72552 rows created.

 

SQL> insert into  t select object_id,object_name from dba_objects;

72552 rows created.

SQL> commit;

 

Commit complete.

SQL> ANALYZE TABLE T COMPUTE STATISTICS;

 

Table analyzed.

SQL> select blocks from user_tables where table_name='T';

 

    BLOCKS

----------

      2062

 

SQL> alter table t enable row movement;

 

Table altered.

 

SQL> alter table t shrink space;

 

 

Table altered.

 

 

SQL> ANALYZE TABLE T COMPUTE STATISTICS;

 

Table analyzed.

 

SQL> select blocks from user_tables where table_name='T';

 

BLOCKS

----------

1950