測試環境：winxp、Oracle9.2

SQL> create table t as select * from dba_objects;

Table created.

SQL> select count(*) from t;

COUNT(*)

----------

30536

SQL> select file_id,block_id,blocks from dba_extents where segment_name='T';

FILE_ID BLOCK_ID BLOCKS

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

1 50921 8

1 50929 8

1 51233 8

1 51241 8

1 51249 8

1 51257 8

1 51265 8

1 51273 8

1 51281 8

1 51289 8

1 51297 8

FILE_ID BLOCK_ID BLOCKS

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

1 51305 8

1 51313 8

1 51321 8

1 51329 8

1 51337 8

1 51465 128

1 51593 128

1 51721 128

19 rows selected.

SQL> show parameter db_file

NAME TYPE VALUE

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

db_file_multiblock_read_count integer 16

db_file_name_convert string

db_files integer 200

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

至此，得到下面的結果，采用的是全表掃描，共掃描了5次。

其中p1是文件號，p2起始塊號，p3讀取數據塊數量。

*** 2006-04-21 11:49:30.000

=====================

PARSING IN CURSOR #1 len=68 dep=0 uid=0 oct=42 lid=0 tim=2925420357 hv=570864185 ad='668b0b0c'

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

END OF STMT

EXEC #1:c=0,e=156,p=0,cr=0,cu=0,mis=1,r=0,dep=0,og=4,tim=2925420341

WAIT #1: nam='SQL*Net message to client' ela= 10 p1=1111838976 p2=1 p3=0

WAIT #1: nam='SQL*Net message from client' ela= 6417020 p1=1111838976 p2=1 p3=0

=====================

PARSING IN CURSOR #1 len=22 dep=0 uid=0 oct=3 lid=0 tim=2931845333 hv=2199322426 ad='6710b08c'

select count(*) from t

END OF STMT

PARSE #1:c=0,e=88,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=2931845326

BINDS #1:

EXEC #1:c=0,e=1534,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=2931853164

WAIT #1: nam='SQL*Net message to client' ela= 9 p1=1111838976 p2=1 p3=0

WAIT #1: nam='db file scattered read' ela= 8813 p1=1 p2=51677 p3=16

WAIT #1: nam='db file scattered read' ela= 1307 p1=1 p2=51693 p3=16

WAIT #1: nam='db file scattered read' ela= 5570 p1=1 p2=51709 p3=12

WAIT #1: nam='db file scattered read' ela= 2616 p1=1 p2=51729 p3=13

WAIT #1: nam='db file scattered read' ela= 595 p1=1 p2=51749 p3=6

FETCH #1:c=15625,e=36032,p=63,cr=421,cu=0,mis=0,r=1,dep=0,og=4,tim=2931890915

WAIT #1: nam='SQL*Net message from client' ela= 409 p1=1111838976 p2=1 p3=0

FETCH #1:c=0,e=4,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=0,tim=2931893361

WAIT #1: nam='SQL*Net message to client' ela= 4 p1=1111838976 p2=1 p3=0

*** 2006-04-21 11:49:52.000

WAIT #1: nam='SQL*Net message from client' ela= 15276041 p1=1111838976 p2=1 p3=0

STAT #1 id=1 cnt=1 pid=0 pos=1 obj=0 op='SORT AGGREGATE '

STAT #1 id=2 cnt=30536 pid=1 pos=1 obj=31687 op='TABLE ACCESS FULL T '

=====================

PARSING IN CURSOR #1 len=55 dep=0 uid=0 oct=42 lid=0 tim=2947176010 hv=3381932903 ad='668aba24'

alter session set events '10046 trace name context off'

END OF STMT

PARSE #1:c=0,e=91,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=2947176003

BINDS #1:

EXEC #1:c=0,e=857,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=2947181612

重新創建一個表空間，其類型為uniform size為1M，在Oracle9.2默認的表空間類型是autoallocate:

SQL> create tablespace test datafile 'd:/oracle/oradata/orcl/test.dbf' size 100m

extent management local uniform size 1m;

Tablespace created.

SQL> alter table t move tablespace test;

Table altered.

SQL> select file_id,block_id,blocks from dba_extents where segment_name='T';

FILE_ID BLOCK_ID BLOCKS

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

15 9 128

15 137 128

15 265 128

15 393 128

SQL> show parameter read_co

NAME TYPE VALUE

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

db_file_multiblock_read_count integer 16

SQL> alter session set db_file_multiblock_read_count=128;

Session altered.

SQL> show parameter read_co

NAME TYPE VALUE

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

db_file_multiblock_read_count integer 128

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

Session altered.

SQL> select count(*) from t;

COUNT(*)

----------

30536

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

Session altered.

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

Session altered.

SQL> select count(object_id) from t;

COUNT(OBJECT_ID)

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

30536

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

Session altered.

*** 2006-04-21 11:57:30.000

=====================

PARSING IN CURSOR #1 len=68 dep=0 uid=0 oct=42 lid=0 tim=3404883601 hv=570864185 ad='668b0b0c'

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

END OF STMT

EXEC #1:c=0,e=107,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3404883596

WAIT #1: nam='SQL*Net message to client' ela= 7 p1=1111838976 p2=1 p3=0

WAIT #1: nam='SQL*Net message from client' ela= 8723581 p1=1111838976 p2=1 p3=0

=====================

PARSING IN CURSOR #1 len=22 dep=0 uid=0 oct=3 lid=0 tim=3413615443 hv=2199322426 ad='6710b08c'

select count(*) from t

END OF STMT

PARSE #1:c=0,e=791,p=0,cr=0,cu=0,mis=1,r=0,dep=0,og=4,tim=3413615434

BINDS #1:

EXEC #1:c=0,e=962,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3413622098

WAIT #1: nam='SQL*Net message to client' ela= 6 p1=1111838976 p2=1 p3=0

WAIT #1: nam='db file scattered read' ela= 26551 p1=15 p2=10 p3=127

WAIT #1: nam='db file scattered read' ela= 21707 p1=15 p2=137 p3=128

WAIT #1: nam='db file scattered read' ela= 21034 p1=15 p2=265 p3=128

WAIT #1: nam='db file scattered read' ela= 6274 p1=15 p2=393 p3=34

FETCH #1:c=31250,e=94765,p=417,cr=421,cu=0,mis=0,r=1,dep=0,og=4,tim=3413718512

WAIT #1: nam='SQL*Net message from client' ela= 405 p1=1111838976 p2=1 p3=0

FETCH #1:c=0,e=3,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=0,tim=3413721284

WAIT #1: nam='SQL*Net message to client' ela= 5 p1=1111838976 p2=1 p3=0

*** 2006-04-21 11:58:34.000

WAIT #1: nam='SQL*Net message from client' ela= 55266334 p1=1111838976 p2=1 p3=0

STAT #1 id=1 cnt=1 pid=0 pos=1 obj=0 op='SORT AGGREGATE '

=====================

PARSING IN CURSOR #2 len=116 dep=1 uid=0 oct=3 lid=0 tim=3468993615 hv=189272129 ad='672eea30'

select o.owner#,o.name,o.namespace,o.remoteowner,o.linkname,o.subname,o.dataobj#,o.flags from obj$ o where o.obj#=:1

END OF STMT

PARSE #2:c=0,e=148,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=3468993604

BINDS #2:

bind 0: dty=2 mxl=22(22) mal=00 scl=00 PRe=00 oacflg=08 oacfl2=1 size=24 offset=0

bfp=05f4a0cc bln=22 avl=04 flg=05

value=31687

EXEC #2:c=0,e=3824,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=3469002280

FETCH #2:c=0,e=78,p=0,cr=3,cu=0,mis=0,r=1,dep=1,og=4,tim=3469003223

STAT #1 id=2 cnt=30536 pid=1 pos=1 obj=31687 op='TABLE ACCESS FULL T '

=====================

PARSING IN CURSOR #1 len=55 dep=0 uid=0 oct=42 lid=0 tim=3469005223 hv=3381932903 ad='668aba24'

alter session set events '10046 trace name context off'

END OF STMT

PARSE #1:c=0,e=86,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3469005215

BINDS #1:

EXEC #1:c=0,e=806,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3469009599

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

Session altered.

SQL> select count(object_id) from t;

COUNT(OBJECT_ID)

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

30536

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

Session altered.

*** 2006-04-21 14:00:39.000

=====================

PARSING IN CURSOR #1 len=68 dep=0 uid=0 oct=42 lid=0 tim=3146410393 hv=570864185 ad='668b0b0c'

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

END OF STMT

EXEC #1:c=0,e=25200,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3146410376

WAIT #1: nam='SQL*Net message to client' ela= 13714 p1=1111838976 p2=1 p3=0

*** 2006-04-21 14:01:05.000

WAIT #1: nam='SQL*Net message from client' ela= 25992096 p1=1111838976 p2=1 p3=0

=====================

PARSING IN CURSOR #1 len=30 dep=0 uid=0 oct=3 lid=0 tim=3172483520 hv=3181685953 ad='66484f6c'

select count(object_id) from t

END OF STMT

PARSE #1:c=0,e=19961,p=0,cr=0,cu=0,mis=1,r=0,dep=0,og=4,tim=3172483510

BINDS #1:

EXEC #1:c=0,e=34883,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3172522525

WAIT #1: nam='SQL*Net message to client' ela= 8 p1=1111838976 p2=1 p3=0

WAIT #1: nam='db file scattered read' ela= 221317 p1=15 p2=10 p3=127

WAIT #1: nam='db file scattered read' ela= 63377 p1=15 p2=137 p3=128

WAIT #1: nam='db file scattered read' ela= 70986 p1=15 p2=265 p3=128

WAIT #1: nam='db file scattered read' ela= 4848 p1=15 p2=393 p3=34

FETCH #1:c=93750,e=390135,p=417,cr=420,cu=0,mis=0,r=1,dep=0,og=4,tim=3172914415

WAIT #1: nam='SQL*Net message from client' ela= 18930 p1=1111838976 p2=1 p3=0

FETCH #1:c=0,e=4,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=0,tim=3172936022

WAIT #1: nam='SQL*Net message to client' ela= 4 p1=1111838976 p2=1 p3=0

WAIT #1: nam='SQL*Net message from client' ela= 3671714 p1=1111838976 p2=1 p3=0

STAT #1 id=1 cnt=1 pid=0 pos=1 obj=0 op='SORT AGGREGATE '

STAT #1 id=2 cnt=30536 pid=1 pos=1 obj=31687 op='TABLE ACCESS FULL T '

=====================

PARSING IN CURSOR #1 len=55 dep=0 uid=0 oct=42 lid=0 tim=3176627539 hv=3381932903 ad='668aba24'

alter session set events '10046 trace name context off'

END OF STMT

PARSE #1:c=0,e=107,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3176627528

BINDS #1:

EXEC #1:c=0,e=889,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3176633060

SQL> create unique index IDX_T_ID on T (object_id);

Index created.

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

Session altered.

SQL> select count(object_id) from t where object_id>0;

COUNT(OBJECT_ID)

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

30536

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

Session altered.

此種情況說明使用了不合理的索引，此時索引使用的是index range掃描方式，從另一個方面也闡述了"db file sequential read"的產生原理。

*** 2006-04-21 14:01:55.000

=====================

PARSING IN CURSOR #1 len=68 dep=0 uid=0 oct=42 lid=0 tim=3222433563 hv=570864185 ad='668b0b0c'

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

END OF STMT

EXEC #1:c=0,e=85,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3222433552

WAIT #1: nam='SQL*Net message to client' ela= 5 p1=1111838976 p2=1 p3=0

*** 2006-04-21 14:02:09.000

WAIT #1: nam='SQL*Net message from client' ela= 14067572 p1=1111838976 p2=1 p3=0

=====================

PARSING IN CURSOR #1 len=48 dep=0 uid=0 oct=3 lid=0 tim=3236513737 hv=1107120101 ad='677ffa8c'

select count(object_id) from t where object_id>0

END OF STMT

PARSE #1:c=0,e=1716,p=0,cr=0,cu=0,mis=1,r=0,dep=0,og=4,tim=3236513728

BINDS #1:

EXEC #1:c=0,e=944,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3236519497

WAIT #1: nam='SQL*Net message to client' ela= 7 p1=1111838976 p2=1 p3=0

WAIT #1: nam='db file sequential read' ela= 12439 p1=1 p2=50923 p3=1

WAIT #1: nam='db file sequential read' ela= 203 p1=1 p2=50924 p3=1

WAIT #1: nam='db file sequential read' ela= 158 p1=1 p2=50925 p3=1

WAIT #1: nam='db file sequential read' ela= 157 p1=1 p2=50926 p3=1

WAIT #1: nam='db file sequential read' ela= 151 p1=1 p2=50927 p3=1

WAIT #1: nam='db file sequential read' ela= 149 p1=1 p2=50928 p3=1

WAIT #1: nam='db file sequential read' ela= 156 p1=1 p2=50929 p3=1

WAIT #1: nam='db file sequential read' ela= 150 p1=1 p2=50930 p3=1

WAIT #1: nam='db file sequential read' ela= 148 p1=1 p2=50931 p3=1

WAIT #1: nam='db file sequential read' ela= 153 p1=1 p2=50932 p3=1

WAIT #1: nam='db file sequential read' ela= 167 p1=1 p2=50933 p3=1

WAIT #1: nam='db file sequential read' ela= 156 p1=1 p2=50934 p3=1

WAIT #1: nam='db file sequential read' ela= 147 p1=1 p2=50935 p3=1

WAIT #1: nam='db file sequential read' ela= 149 p1=1 p2=50936 p3=1

WAIT #1: nam='db file sequential read' ela= 1330 p1=1 p2=51233 p3=1

WAIT #1: nam='db file sequential read' ela= 153 p1=1 p2=51234 p3=1

WAIT #1: nam='db file sequential read' ela= 149 p1=1 p2=51235 p3=1

WAIT #1: nam='db file sequential read' ela= 142 p1=1 p2=51236 p3=1

WAIT #1: nam='db file sequential read' ela= 152 p1=1 p2=51237 p3=1

WAIT #1: nam='db file sequential read' ela= 153 p1=1 p2=51238 p3=1

WAIT #1: nam='db file sequential read' ela= 152 p1=1 p2=51239 p3=1

WAIT #1: nam='db file sequential read' ela= 146 p1=1 p2=51240 p3=1

WAIT #1: nam='db file sequential read' ela= 203 p1=1 p2=51241 p3=1

WAIT #1: nam='db file sequential read' ela= 158 p1=1 p2=51242 p3=1

WAIT #1: nam='db file sequential read' ela= 158 p1=1 p2=51243 p3=1

WAIT #1: nam='db file sequential read' ela= 153 p1=1 p2=51244 p3=1

WAIT #1: nam='db file sequential read' ela= 158 p1=1 p2=51245 p3=1

WAIT #1: nam='db file sequential read' ela= 154 p1=1 p2=51246 p3=1

WAIT #1: nam='db file sequential read' ela= 152 p1=1 p2=51247 p3=1

WAIT #1: nam='db file sequential read' ela= 153 p1=1 p2=51248 p3=1

WAIT #1: nam='db file sequential read' ela= 153 p1=1 p2=51249 p3=1

WAIT #1: nam='db file sequential read' ela= 172 p1=1 p2=51250 p3=1

WAIT #1: nam='db file sequential read' ela= 153 p1=1 p2=51251 p3=1

WAIT #1: nam='db file sequential read' ela= 213 p1=1 p2=51252 p3=1

WAIT #1: nam='db file sequential read' ela= 166 p1=1 p2=51253 p3=1

WAIT #1: nam='db file sequential read' ela= 156 p1=1 p2=51254 p3=1

WAIT #1: nam='db file sequential read' ela= 152 p1=1 p2=51255 p3=1

WAIT #1: nam='db file sequential read' ela= 154 p1=1 p2=51256 p3=1

WAIT #1: nam='db file sequential read' ela= 156 p1=1 p2=51257 p3=1

WAIT #1: nam='db file sequential read' ela= 154 p1=1 p2=51258 p3=1

WAIT #1: nam='db file sequential read' ela= 171 p1=1 p2=51259 p3=1

WAIT #1: nam='db file sequential read' ela= 156 p1=1 p2=51260 p3=1

WAIT #1: nam='db file sequential read' ela= 152 p1=1 p2=51261 p3=1

WAIT #1: nam='db file sequential read' ela= 151 p1=1 p2=51262 p3=1

WAIT #1: nam='db file sequential read' ela= 149 p1=1 p2=51263 p3=1

WAIT #1: nam='db file sequential read' ela= 147 p1=1 p2=51264 p3=1

WAIT #1: nam='db file sequential read' ela= 150 p1=1 p2=51265 p3=1

WAIT #1: nam='db file sequential read' ela= 151 p1=1 p2=51266 p3=1

WAIT #1: nam='db file sequential read' ela= 140 p1=1 p2=51267 p3=1

WAIT #1: nam='db file sequential read' ela= 151 p1=1 p2=51268 p3=1

WAIT #1: nam='db file sequential read' ela= 152 p1=1 p2=51269 p3=1

WAIT #1: nam='db file sequential read' ela= 146 p1=1 p2=51270 p3=1

WAIT #1: nam='db file sequential read' ela= 148 p1=1 p2=51271 p3=1

WAIT #1: nam='db file sequential read' ela= 199 p1=1 p2=51272 p3=1

WAIT #1: nam='db file sequential read' ela= 158 p1=1 p2=51273 p3=1

WAIT #1: nam='db file sequential read' ela= 154 p1=1 p2=51274 p3=1

WAIT #1: nam='db file sequential read' ela= 154 p1=1 p2=51275 p3=1

WAIT #1: nam='db file sequential read' ela= 153 p1=1 p2=51276 p3=1

WAIT #1: nam='db file sequential read' ela= 151 p1=1 p2=51277 p3=1

WAIT #1: nam='db file sequential read' ela= 152 p1=1 p2=51278 p3=1

WAIT #1: nam='db file sequential read' ela= 151 p1=1 p2=51279 p3=1

WAIT #1: nam='db file sequential read' ela= 150 p1=1 p2=51280 p3=1

WAIT #1: nam='db file sequential read' ela= 148 p1=1 p2=51281 p3=1

FETCH #1:c=15625,e=102159,p=63,cr=64,cu=0,mis=0,r=1,dep=0,og=4,tim=3236628878

WAIT #1: nam='SQL*Net message from client' ela= 382 p1=1111838976 p2=1 p3=0

FETCH #1:c=0,e=2,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=0,tim=3236631569

WAIT #1: nam='SQL*Net message to client' ela= 4 p1=1111838976 p2=1 p3=0

WAIT #1: nam='SQL*Net message from client' ela= 3303736 p1=1111838976 p2=1 p3=0

STAT #1 id=1 cnt=1 pid=0 pos=1 obj=0 op='SORT AGGREGATE '

STAT #1 id=2 cnt=30536 pid=1 pos=1 obj=31689 op='INDEX RANGE SCAN IDX_T_ID '

=====================

PARSING IN CURSOR #1 len=55 dep=0 uid=0 oct=42 lid=0 tim=3239940284 hv=3381932903 ad='668aba24'

alter session set events '10046 trace name context off'

END OF STMT

PARSE #1:c=0,e=92,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3239940275

BINDS #1:

EXEC #1:c=0,e=1028,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3239947806

SQL> analyze table t compute statistics;

Table analyzed.

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

Session altered.

SQL> select count(object_id) from t where object_id>0;

COUNT(OBJECT_ID)

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

30536

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

Session altered.

這個現象說明假如表是被分析過的話，采用的就是CBO：

*** 2006-04-21 14:10:18.000

=====================

PARSING IN CURSOR #1 len=68 dep=0 uid=0 oct=42 lid=0 tim=3724965605 hv=570864185 ad='668b0b0c'

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

END OF STMT

EXEC #1:c=0,e=153,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3724965598

WAIT #1: nam='SQL*Net message to client' ela= 7 p1=1111838976 p2=1 p3=0

*** 2006-04-21 14:10:28.000

WAIT #1: nam='SQL*Net message from client' ela= 10044728 p1=1111838976 p2=1 p3=0

=====================

PARSING IN CURSOR #1 len=48 dep=0 uid=0 oct=3 lid=0 tim=3735044065 hv=1107120101 ad='677ffa8c'

select count(object_id) from t where object_id>0

END OF STMT

PARSE #1:c=0,e=18398,p=0,cr=0,cu=0,mis=1,r=0,dep=0,og=4,tim=3735044052

BINDS #1:

EXEC #1:c=0,e=908,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3735050327

WAIT #1: nam='SQL*Net message to client' ela= 5 p1=1111838976 p2=1 p3=0

FETCH #1:c=15625,e=16491,p=0,cr=68,cu=0,mis=0,r=1,dep=0,og=4,tim=3735068413

WAIT #1: nam='SQL*Net message from client' ela= 470 p1=1111838976 p2=1 p3=0

FETCH #1:c=0,e=4,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=0,tim=3735071416

WAIT #1: nam='SQL*Net message to client' ela= 6 p1=1111838976 p2=1 p3=0

WAIT #1: nam='SQL*Net message from client' ela= 3767452 p1=1111838976 p2=1 p3=0

STAT #1 id=1 cnt=1 pid=0 pos=1 obj=0 op='SORT AGGREGATE '

STAT #1 id=2 cnt=30536 pid=1 pos=1 obj=31690 op='INDEX FAST FULL SCAN IDX_T_ID '

=====================

PARSING IN CURSOR #1 len=55 dep=0 uid=0 oct=42 lid=0 tim=3738845289 hv=3381932903 ad='668aba24'

alter session set events '10046 trace name context off'

END OF STMT

PARSE #1:c=0,e=91,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3738845282

BINDS #1:

EXEC #1:c=0,e=876,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=4,tim=3738850186