模拟Direct Path write

       数据被直接读取到PGA内存中时，发生的等待，如排序由于内存不足，被写到磁盘上，然后重新读取。为了在v$session_wait中看到，在公司的环境上找了一个大表，进行测试，建大表的步骤省略。
session1:
SQL> select * from v$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> select distinct sid from v$mystat;

       SID
----------
       139     
SQL> alter system set pga_aggregate_target = 1M;
SQL> alter session set tracefile_identifier = '11111111';
SQL> set autotrace traceonly;
SQL> alter session set events '10046 trace name context forever ,level 12' ;
SQL> create table TEST_DPW as select * from TEST_DPR;

session2:
SQL> select sid,event from v$session_wait w where w.SID = 139;
       SID EVENT
---------- ----------------------------------------------------------------
       139 SQL*Net message from client
SQL> /
       SID EVENT
---------- ----------------------------------------------------------------
       139 direct path write
SQL> /
       SID EVENT
---------- ----------------------------------------------------------------
       139 direct path write

session3:
create table TEST_DPW as select * from TEST_DPR

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.07          0          1          0           0
Execute      1      1.26      17.32      30345      30646      34068     1085999
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        2      1.26      17.40      30345      30647      34068     1085999

Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 84 
Rows     Row Source Operation
-------  ---------------------------------------------------
      0  LOAD AS SELECT  (cr=31506 pr=30345 pw=30345 time=0 us)
1085999   TABLE ACCESS FULL TEST_DPR (cr=30350 pr=30345 pw=0 time=617937 us cost=8310 size=3046085760 card=1312968)

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  Disk file operations I/O                       15        0.13          0.60
  direct path read                               62        0.16          2.88
  direct path write                             679        0.18          7.65
  control file sequential read                   84        0.07          0.58
  db file sequential read                         8        0.00          0.03
  Data file init write                            4        0.00          0.00
  db file single write                            4        0.00          0.00
  control file parallel write                    12        0.00          0.00
  rdbms ipc reply                                 4        0.10          0.13
  buffer busy waits                               3        0.72          1.91
  asynch descriptor resize                        2        0.00          0.00
  log file sync                                   1        0.00          0.00
  SQL*Net message to client                       1        0.00          0.00
  SQL*Net message from client                     1       21.20         21.20
********************************************************************************