OWI之direct path write

<p style="padding-top: 6px; padding-bottom: 6px; margin-top: 0px; margin-bottom: 0px; color: rgb(51, 51, 51); font-family: 'Trebuchet MS', Tahoma, Arial; line-height: 18px; "><pre name="code" class="sql">直接路径写（direct paht write）通常发生在Oracle直接从PGA写数据到数据文件或临时文件，这个写操作可以绕过SGA。直接路径写等待事件的3个参数分别是：file number（指绝对文件号）、first dba和block cnt数量，在Oracle 10g/11g中，这个等待事件同direct path read一样被归于User I/O一类。
这类写入操作通常在以下情况被使用：
·直接路径加载；
·并行DML操作；
·磁盘排序；
·对未缓存的“LOB”段的写入，随后会记录为direct path write(lob)等待。

SQL> select * from v$mystat where rownum<2;

       SID STATISTIC#	   VALUE
---------- ---------- ----------
       192	    0	       0

SQL> create table test1 as select * from F_AGT_GCI_BUSINESS_INFO_H;

SQL> select sid,event,p1,p2,p3 from v$session_wait where sid=192;

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path read							    14	  1746176	 128

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path write							     8	  3446368	  32

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path read							     9	  1760896	 128

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path read							     7	  1795968	 128

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path write							    21	  3394464	  32

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path read							    21	  1769984	 128

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path read							    20	  1772672	 128

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path write							    16	  3360288	  32

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path write							    14	  3328384	  32

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path write							    13	  3316992	  32

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path write							    12	  3317696	  32

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path read							    13	  1729032	 120

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path read							    12	  1734784	 128

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path read							    11	  1745152	 128

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path write							     7	  3467584	  32

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path read							    10	  1751296	 128

SQL> /

       SID EVENT								    P1	       P2	  P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       192 direct path write							     5	  3406944	  32


direct path write 稳定在32左右

 direct path read/write 都是通过server process读写的吧