模拟direct path read

       直接路径读（direct path read）通常发生在Oracle直接读数据到进程PGA时，这个读取不需要经过SGA。直接路径读等待事件的3个参数分别是file number（指绝对文件号）、first dba、block cnt数量。在Oracle 10g/11g中，这个等待事件被归于User I/O一类。如何模拟出来呢？把PGA设置小一点，弄一张大表做排序。

session1:
SQL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for 32-bit Windows: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

SQL> alter system set pga_aggregate_target = 1M;
SQL> select count(1) from TEST_DPR;

  COUNT(1)
----------
   1085999
SQL> select distinct sid from v$mystat;
       SID
----------
        18
SQL> alter session set tracefile_identifier = '11111111';
SQL> set autotrace traceonly;
SQL> alter session set events '10046 trace name context forever ,level 12' ;
SQL> select * from TEST_DPR order by record_content;

session2:
SQL> select sid,event from v$session_wait w where w.SID = 18;
       SID EVENT
---------- ----------------------------------------------------------------
        18 SQL*Net message from client
SQL> /
       SID EVENT
---------- ----------------------------------------------------------------
        18 direct path read
SQL> /
       SID EVENT
---------- ----------------------------------------------------------------
        18 direct path write temp
SQL> /
       SID EVENT
---------- ----------------------------------------------------------------
        18 direct path write temp

session3:
E:\oracle11g\guogang\diag\rdbms\orcl\orcl\trace>tkprof orcl_ora_4616_11111111.trc  111.txt sys=no aggregate=no

select *
from
 TEST_DPR order by record_content

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    72401      6.04      18.20      60539      30350          6     1085999
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total    72403      6.04      18.20      60539      30350          6     1085999

Misses in library cache during parse: 0
Optimizer mode: ALL_ROWS
Parsing user id: 84 

Rows     Row Source Operation
-------  ---------------------------------------------------
1085999  SORT ORDER BY (cr=30350 pr=60539 pw=30194 time=2977534 us cost=643568 size=3046085760 card=1312968)
1085999   TABLE ACCESS FULL TEST_DPR (cr=30350 pr=30345 pw=0 time=1711998 us cost=8310 size=3046085760 card=1312968)

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                   72401        0.00          0.04
  Disk file operations I/O                        2        0.00          0.00
  direct path read                              241        0.14          2.39
  direct path write temp                        966        0.15          5.32
  asynch descriptor resize                        3        0.00          0.00
  direct path read temp                        1071        0.06          3.93
  SQL*Net message from client                 72401        0.00         31.69
  SQL*Net more data to client                    64        0.00          0.00
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