Oracle INDEX FAST FULL SCAN与 INDEX FULL SCAN

  两种常见的索引扫描方式：INDEX FAST FULL SCAN，INDEX FULL SCAN。前者是按照索引的物理结构扫描（就是高水位线以下），后者是按照索引的逻辑结构，即树形结构，叶子节点的双向链表扫描数据。

--制造一些数据

drop table test purge;
create table test as select * from dba_objects where object_id is not null;
alter table test modify object_id not null;
create unique index ind_object_id on test(object_id) nologging;
create index ind_object_name on test(object_name) nologging;
exec dbms_stats.gather_table_stats(user,'test',cascade => true);

--执行测试脚本

alter system flush buffer_cache;

set autotrace traceonly
alter session set events '10046 trace name context forever ,level 12' ;
select object_id from test;
alter session set events '10046 trace name context off' ;

alter system flush buffer_cache;
set autotrace traceonly
alter session set events '10046 trace name context forever ,level 12' ;
select * from test order by object_id;
alter session set events '10046 trace name context off' ;

select object_id 
from
 test
call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch     4847      0.15       0.14        153       4992          0       72683
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total     4849      0.15       0.15        153       4992          0       72683
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 79  
Rows     Row Source Operation
-------  ---------------------------------------------------

  72683  INDEX FAST FULL SCAN IND_OBJECT_ID (cr=4992 pr=153 pw=0 time=25509 us cost=43 size=363415 card=72683)(object id 75710)

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                    4847        0.00          0.00
  db file sequential read                         1        0.00          0.00
  db file scattered read                17        0.00          0.01
  SQL*Net message from client                  4847        0.00          0.19
********************************************************************************


select * 
from
 test order by object_id
call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch     4847      0.24       0.42       1232      10845          0       72683
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total     4849      0.24       0.42       1232      10845          0       72683
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 79  
Rows     Row Source Operation
-------  ---------------------------------------------------
  72683  TABLE ACCESS BY INDEX ROWID TEST (cr=10845 pr=1232 pw=0 time=251374 us cost=1244 size=7050251 card=72683)
  72683   INDEX FULL SCAN IND_OBJECT_ID (cr=4985 pr=168 pw=0 time=25336 us cost=153 size=0 card=72683)(object id 75710)

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                    4847        0.00          0.00
  db file scattered read               154        0.07          0.20
  SQL*Net message from client                  4847        0.00          1.06
********************************************************************************