[20121025]1条记录会有多少row pieces.txt

[20121025]1条记录会有多少row pieces.txt
jonathan lewis出了一道题目Quiz,参考这个链接:
http://jonathanlewis.wordpress.com/2012/03/30/quiz-night-17/
create table t1 (
        col000  number(1),
        col001  number(1),
        col002  number(1),
...
        col997  number(1),
        col998  number(1),
        col999  number(1),
        constraint t1_pk primary key (col000)
)
;
How many row pieces might that row consist of ?
自己做一些测试:
1.环境如下:
SQL> select * from v$version where rownum
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production


2.建表方法:


spool a.sql


select 'create table t1 (' from dual 


union all


select 'col'||lpad(rownum-1,3,'0')||' number(1),' from dual connect by level


union all 


select 'constraint t1_pk primary key (col000));' from dual ;


spool b.sql


select 'INSERT into t1 VALUES (' from dual


union all


select '1,' from dual connect by level


union all


select ' 1);' from dual ;


SQL> select rowid from t1;


ROWID


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


AAAcRpAAEAAAAIPAAD


SQL> @ lookup_rowid AAAcRpAAEAAAAIPAAD


    OBJECT       FILE      BLOCK        ROW


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


    115817          4        527          3




SQL> alter system checkpoint;


System altered.


BBED> set dba 4,527


        DBA             0x0100020f (16777743 4,527)


BBED> map /v


 File: /u01/app/oracle11g/oradata/test/users01.dbf (4)


 Block: 527                                   Dba:0x0100020f


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


 KTB Data Block (Table/Cluster)


.....


 sb2 kdbr[4]                                @166


 ub1 freespace[4984]                        @174


 ub1 rowdata[3030]                          @5158


 ub4 tailchk                                @8188


--我仅仅插入一条记录,可以发现sb2 kdbr[4] @166,有4个目录.


BBED> p *kdbr[0]


rowdata[2262]


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


ub1 rowdata[2262]                           @7420     0x04


BBED> x /rn


rowdata[2262]                               @7420


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


flag@7420: 0x04 (KDRHFL)


lock@7421: 0x01


cols@7422:  255


col    0[2] @7423: 1


col    1[2] @7426: 1


........


col  253[2] @8182: 1


col  254[2] @8185: 1


--一个行目录有255个字段.


2.重新测试(如果插入几个字段,在修改其他呢?):


SQL> drop table t1 purge;


Table dropped.


SQL> @a.sql


Table created.


SQL> insert into t1(col000) values(1);


SQL> commit;


SQL> select rowid from t1;


ROWID


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


AAAcS5AAEAAAAIPAAA


SQL> @ lookup_rowid AAAcS5AAEAAAAIPAAA


    OBJECT       FILE      BLOCK        ROW


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


    115897          4        527          0




现在执行如下:


begin


for i in 255..999 loop


 execute immediate 'update t1 set col'||i||'=0';


 end loop;


commit;


end;


/


SQL> alter system checkpoint;


System altered.


BBED> set dba 4,527


        DBA             0x0100020f (16777743 4,527)


BBED> map /v


 File: /u01/app/oracle11g/oradata/test/users01.dbf (4)


 Block: 527                                   Dba:0x0100020f


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


 KTB Data Block (Table/Cluster)


....


 sb2 kdbr[1]                                @118


 ub1 freespace[8050]                        @120


 ub1 rowdata[18]                            @8170


 ub4 tailchk                                @8188


BBED> p *kdbr[0]


rowdata[0]


----------


ub1 rowdata[0]                              @8170     0x28


BBED> x /rn


rowdata[0]                                  @8170


----------


flag@8170: 0x28 (KDRHFF, KDRHFH)


lock@8171: 0x02


cols@8172:    1


nrid@8173:0x0100020b.0


col    0[2] @8179: 1


--nrid表示其他信息在0x0100020b.0,在dba=0x0100020b,row=0的位置.


BBED>  set dba 0x0100020b


        DBA             0x0100020b (16777739 4,523)


BBED> map /v


 File: /u01/app/oracle11g/oradata/test/users01.dbf (4)


 Block: 523                                   Dba:0x0100020b


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


 KTB Data Block (Table/Cluster)


...


 sb2 kdbr[1]                                @142


 ub1 freespace[7785]                        @144


 ub1 rowdata[259]                           @7929


 ub4 tailchk                                @8188


--仅仅一个行目录.


BBED> x /rn


rowdata[0]                                  @7929


----------


flag@7929: 0x00 (NONE)


lock@7930: 0x01


cols@7931:    1


nrid@7932:0x0100020c.0


col    0[0] @7938: *NULL*


--注意仅仅一个字段,内容为空.也就是表的col001字段.


SQL> exec dbms_stats.gather_table_stats(user, 't1', method_opt=>'for all columns size 1');


PL/SQL procedure successfully completed.


SQL> column segment_name format a20


SQL> select segment_name,segment_subtype,bytes,blocks,extents,initial_extent,next_extent from dba_segments where wner=user and segment_name='T1';


SEGMENT_NAME         SEGMENT_SU      BYTES     BLOCKS    EXTENTS INITIAL_EXTENT NEXT_EXTENT


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


T1                   ASSM          6291456        768         21          65536     1048576


--可以发现占用768块,extents=21.


SQL> select segment_name,segment_type,extent_id,file_id,block_id,bytes,blocks,relative_fno from dba_extents where wner=user and segment_name='T1';


SEGMENT_NAME         SEGMENT_TYPE        EXTENT_ID    FILE_ID   BLOCK_ID      BYTES     BLOCKS RELATIVE_FNO


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


T1                   TABLE                       0          4        520      65536          8            4


T1                   TABLE                       1          4        552      65536          8            4


T1                   TABLE                       2          4        568      65536          8            4


T1                   TABLE                       3          4        584      65536          8            4


T1                   TABLE                       4          4        608      65536          8            4


T1                   TABLE                       5          4        624      65536          8            4


T1                   TABLE                       6          4        632      65536          8            4


T1                   TABLE                       7          4       1792      65536          8            4


T1                   TABLE                       8          4       1800      65536          8            4


T1                   TABLE                       9          4       1808      65536          8            4


T1                   TABLE                      10          4       1816      65536          8            4


T1                   TABLE                      11          4       1824      65536          8            4


T1                   TABLE                      12          4       1832      65536          8            4


T1                   TABLE                      13          4       1840      65536          8            4


T1                   TABLE                      14          4       1848      65536          8            4


T1                   TABLE                      15          4       1856      65536          8            4


T1                   TABLE                      16          4        640    1048576        128            4


T1                   TABLE                      17          4        768    1048576        128            4


T1                   TABLE                      18          4        896    1048576        128            4


T1                   TABLE                      19          4       1024    1048576        128            4


T1                   TABLE                      20          4       1152    1048576        128            4


21 rows selected.


--仅仅1条记录占用这么多块.


SQL> set autotrace traceonly


--注意我使用hint,通过索引访问


SQL> select /*+ index(t1) */ col999 from t1 where col000=1;


Execution Plan


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


Plan hash value: 2347959165


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


| Id  | Operation                   | Name  | Rows  | Bytes | Cost (%CPU)| Time     |


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


|   0 | SELECT STATEMENT            |       |     1 |     5 |     1   (0)| 00:00:01 |


|   1 |  TABLE ACCESS BY INDEX ROWID| T1    |     1 |     5 |     1   (0)| 00:00:01 |


|*  2 |   INDEX UNIQUE SCAN         | T1_PK |     1 |       |     0   (0)| 00:00:01 |


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


Predicate Information (identified by operation id):


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


   2 - access("COL000"=1)


Statistics


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


          1  recursive calls


          0  db block gets


        747  consistent gets


          0  physical reads


          0  redo size


        523  bytes sent via SQL*Net to client


        520  bytes received via SQL*Net from client


          2  SQL*Net roundtrips to/from client


          0  sorts (memory)


          0  sorts (disk)


          1  rows processed


--访问col999,consistent gets高达747.




SQL> select /*+ index(t1) */ col001 from t1 where col000=1;


Execution Plan


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


Plan hash value: 2347959165


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


| Id  | Operation                   | Name  | Rows  | Bytes | Cost (%CPU)| Time     |


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


|   0 | SELECT STATEMENT            |       |     1 |    16 |     1   (0)| 00:00:01 |


|   1 |  TABLE ACCESS BY INDEX ROWID| T1    |     1 |    16 |     1   (0)| 00:00:01 |


|*  2 |   INDEX UNIQUE SCAN         | T1_PK |     1 |       |     0   (0)| 00:00:01 |


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


Predicate Information (identified by operation id):


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


   2 - access("COL000"=1)




Statistics


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


          0  recursive calls


          0  db block gets


          3  consistent gets


          0  physical reads


          0  redo size


        522  bytes sent via SQL*Net to client


        520  bytes received via SQL*Net from client


          2  SQL*Net roundtrips to/from client


          0  sorts (memory)


          0  sorts (disk)


          1  rows processed


SQL> select /*+ index(t1) */ col002 from t1 where col000=1;




Execution Plan


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


Plan hash value: 2347959165


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


| Id  | Operation                   | Name  | Rows  | Bytes | Cost (%CPU)| Time     |


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


|   0 | SELECT STATEMENT            |       |     1 |    16 |     1   (0)| 00:00:01 |


|   1 |  TABLE ACCESS BY INDEX ROWID| T1    |     1 |    16 |     1   (0)| 00:00:01 |


|*  2 |   INDEX UNIQUE SCAN         | T1_PK |     1 |       |     0   (0)| 00:00:01 |


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


Predicate Information (identified by operation id):


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


   2 - access("COL000"=1)




Statistics


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


          0  recursive calls


          0  db block gets


          4  consistent gets


          0  physical reads


          0  redo size


        522  bytes sent via SQL*Net to client


        520  bytes received via SQL*Net from client


          2  SQL*Net roundtrips to/from client


          0  sorts (memory)


          0  sorts (disk)


          1  rows processed


--col002需要4个consistent gets,col001需要3个consistent gets.说明存在行链接情况.


alter system flush buffer_cache; --刷新buffer cache.


alter session set events '10046 trace name context forever, level 12';


select /*+ index(t1) */ col255 from t1 where col000=1;


alter session set events '10046 trace name context off';


$ grep 'db file sequential read' /u01/app/oracle11g/diag/rdbms/test/test/trace/test_ora_7578.trc| grep obj#=115897| tail -10


WAIT #2: nam='db file sequential read' ela= 25 file#=4 block#=859 blocks=1 obj#=115897 tim=1351136716474142


WAIT #2: nam='db file sequential read' ela= 20 file#=4 block#=863 blocks=1 obj#=115897 tim=1351136716474222


WAIT #2: nam='db file sequential read' ela= 22 file#=4 block#=867 blocks=1 obj#=115897 tim=1351136716474344


WAIT #2: nam='db file sequential read' ela= 19 file#=4 block#=871 blocks=1 obj#=115897 tim=1351136716474422


WAIT #2: nam='db file sequential read' ela= 19 file#=4 block#=875 blocks=1 obj#=115897 tim=1351136716474503


WAIT #2: nam='db file sequential read' ela= 19 file#=4 block#=879 blocks=1 obj#=115897 tim=1351136716474567


WAIT #2: nam='db file sequential read' ela= 16 file#=4 block#=883 blocks=1 obj#=115897 tim=1351136716474625


WAIT #2: nam='db file sequential read' ela= 16 file#=4 block#=887 blocks=1 obj#=115897 tim=1351136716474681


WAIT #2: nam='db file sequential read' ela= 15 file#=4 block#=891 blocks=1 obj#=115897 tim=1351136716474736


WAIT #2: nam='db file sequential read' ela= 15 file#=4 block#=895 blocks=1 obj#=115897 tim=1351136716474795


$ grep 'db file sequential read' /u01/app/oracle11g/diag/rdbms/test/test/trace/test_ora_7578.trc| grep obj#=115897| wc


    256    3328   27716


--读取了256次表T1.另外可以看到assm管理模式插入到后面时数据块的分配情况,相隔4块.(859->863->867...).


BBED> set dba 4,895


        DBA             0x0100037f (16778111 4,895)


BBED> p *kdbr[0]


rowdata[0]


----------


ub1 rowdata[0]                              @7675     0x00


BBED> x /rnnnn


rowdata[0]                                  @7675


----------


flag@7675: 0x00 (NONE)


lock@7676: 0x01


cols@7677:    1


nrid@7678:0x01000340.0


col    0[1] @7684: 0


--正好对应col255的值.


3.一点疑问:


前面我们执行select /*+ index(t1) */ col999 from t1 where col000=1;仅仅747逻辑读,按照前面的介绍,都是1块保存1个字段,按照道理


逻辑读应该在1000以上.在做如下测试看看.


alter system flush buffer_cache; --刷新buffer cache.


alter session set events '10046 trace name context forever, level 12';


select /*+ index(t1) */ col255 from t1 where col000=1;


alter session set events '10046 trace name context off';


$ grep 'db file sequential read' /u01/app/oracle11g/diag/rdbms/test/test/trace/test_ora_17897.trc| grep obj#=115897|wc


    746    9698   80910


--确实读取746次.这样讲有些块应该保存几个字段.


--取出块


$ grep 'db file sequential read' test_ora_17897.trc| grep obj#=115897|cut -d"=" -f5 | cut -d' ' -f1 > /tmp/aa1.txt


--使用vi编辑aa1.txt,^M相当于回车,使用ctrl-v+ctrl+M输入.


:%s/^/set dba 4,/


:%s+$+^Mp *kdbr[0]^Mx /rnnnnn+


开头加入


set count 8192


set width 210


结尾加入


quit


参数文件里面如下:


$ cat bbedreadonly.par


blocksize=8192


listfile=/home/oracle11g/bbed/filelist.txt


mode=browse


PASSWORD=blockedit


spool=yes


$ /u01/app/oracle11g/product/11.2.0/db_1/bin/bbed parfile=bbedreadonly.par cmdfile=/tmp/aa1.txt


--检查log.bbd文件.


BBED> set dba 4,1171


    DBA             0x01000493 (16778387 4,1171)


BBED> p *kdbr[0]


rowdata[0]


----------


ub1 rowdata[0]                              @7675     0x04


BBED> x /rnnnnn


rowdata[0]                                  @7675


----------


flag@7675: 0x04 (KDRHFL)


lock@7676: 0x01


cols@7677:  255


col    0[1] @7678: 0


col    1[1] @7680: 0


col    2[1] @7682: 0


...


col  244[1] @8166: 0


col  245[1] @8168: 0


col  246[1] @8170: 0


col  247[1] @8172: 0


col  248[1] @8174: 0


col  249[1] @8176: 0


col  250[1] @8178: 0


col  251[1] @8180: 0


col  252[1] @8182: 0


col  253[1] @8184: 0


col  254[1] @8186: 0


--可以发现读取的最后1块,dba=4,1171,保存最后255个字段. 999-255+1=745,这么讲col745~colcol999在一个块中(dba=4,1171)


SQL> set autotrace traceonly


SQL> select /*+ index(t1) */ col745 from t1 where col000=1;


Execution Plan


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


Plan hash value: 2347959165


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


| Id  | Operation                   | Name  | Rows  | Bytes | Cost (%CPU)| Time     |


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


|   0 | SELECT STATEMENT            |       |     1 |     5 |     1   (0)| 00:00:01 |


|   1 |  TABLE ACCESS BY INDEX ROWID| T1    |     1 |     5 |     1   (0)| 00:00:01 |


|*  2 |   INDEX UNIQUE SCAN         | T1_PK |     1 |       |     0   (0)| 00:00:01 |


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


Predicate Information (identified by operation id):


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


   2 - access("COL000"=1)




Statistics


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


          0  recursive calls


          0  db block gets


        747  consistent gets


          0  physical reads


          0  redo size


        523  bytes sent via SQL*Net to client


        520  bytes received via SQL*Net from client


          2  SQL*Net roundtrips to/from client


          0  sorts (memory)


          0  sorts (disk)


          1  rows processed


--逻辑读与执行select /*+ index(t1) */ col999 from t1 where col000=1;一样.


总结:


1.建立表字段太多不好,如果太多超过255,可能的话可以根据业务需要拆分多个表.


2.如果一个表的字段很多,操作模式先insert一些字段,然后update后面字段多次,并且是分许多次的情况下,可能出出现这种情况.


我管的系统没有这么多的字段.按照链接的介绍,这种情况出现在像Siebel应用很常见.




				


				
时间： 2024-10-24 17:04:14

		
		


		


	

	
	

		


		
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