最近在看吕大师的大作《Oracle核心揭密》，马上要上市了，期待中。。。
这部大作可以与Jonathan Lewis大师的《Oracle Core_ Essential Internals for DBA》相提并论，看了几天收益颇多，哈哈美国有Lewis，中国有VAGE。
[email protected]> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
[email protected]> show parameter mem
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
hi_shared_memory_address integer 0
memory_max_target big integer 0
memory_target big integer 0
shared_memory_address integer 0
[email protected]> show parameter sga
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
lock_sga boolean FALSE
pre_page_sga boolean FALSE
sga_max_size big integer 372M
sga_target big integer 0
[email protected]> show parameter db_cache
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_cache_advice string ON
db_cache_size big integer 100M
[email protected]> show parameter mttr
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
fast_start_mttr_target integer 0
_db_writer_coalesce_area_size Size of memory allocated to dbwriter for coalescin 1048576
[email protected]>create table gyj100 (id int,name varchar2(2000));
[email protected]> declare
2 c number :=0 ;
3 begin
4 for i in 1 .. 5000000 loop
5 insert into gyj100 values(i,'gyj'||i);
6 c := c+1;
7 if mod(c,5000)=0 then
8 commit;
9 end if;
10 end loop;
11 end;
12 /
PL/SQL procedure successfully completed.
[email protected]> select bytes/1024/1024 sz from user_segments where segment_name='GYJ100';
SZ
----------
120
[email protected]> select sid from v$mystat where rownum=1;
SID
----------
125
[email protected]> update gyj100 set id=id+0 where rownum<=5000000;
5000000 rows updated.
Elapsed: 00:00:47.50
再开一个窗口观察等待事件：
[email protected]> select * from V$SESSION_wait where sid=125;
SID SEQ# EVENT P1TEXT P1 P1RAW P2TEXT P2 P2RAW P3TEXT P3 P3RAW WAIT_CLASS_ID WAIT_CLASS# WAIT_CLASS WAIT_TIME SECONDS_IN_WAIT STATE WAIT_TIME_MICRO TIME_REMAINING_MICRO TIME_SINCE_LAST_WAIT_MICRO
---------- ---------- ---------------------------------------------------------------- ---------------------------------------------------------------- ---------- ---------------- ---------------------------------------------------------------- ---------- ---------------- ---------------------------------------------------------------- ---------- ---------------- ------------- ----------- ---------------------------------------------------------------- ---------- --------------- ------------------- --------------- -------------------- --------------------------
125 45323 log buffer space 0 00 0 00 0 00 3290255840 2 Configuration -1 0 WAITED SHORT TIME 4608 7446
[email protected]> select event,TOTAL_WAITS , TIME_WAITED_MICRO from V$SYSTEM_EVENT where EVENT='db file parallel write';
no rows selected
[email protected]> select event,TOTAL_WAITS , TIME_WAITED_MICRO from V$SYSTEM_EVENT where EVENT like 'db file%';
EVENT TOTAL_WAITS TIME_WAITED_MICRO
---------------------------------------------------------------- ----------- -----------------
db file sequential read 91162 37712572
db file scattered read 1830 8543678
db file single write 372 1934286
db file async I/O submit 553 84199251
db file parallel read 67 1863758
始终没看到db file parallel write等待。。。。
在吕大师的指点下：
select event,TOTAL_WAITS , TIME_WAITED_MICRO from V$SYSTEM_EVENT where EVENT='db file async I/O submit';
MOS上有篇文章
'db file async I/O submit' when FILESYSTEMIO_OPTIONS=NONE [ID 1274737.1]
'db file async I/O submit' should be treated as 'db file parallel write' in previous releases.
**********************************************************************
在吕大的指点下，开始测试：
**********************************************************************
第一把：
参数：_db_writer_coalesce_area_size=1048576
[email protected]> select event,TOTAL_WAITS , TIME_WAITED_MICRO from V$SYSTEM_EVENT where EVENT='db file async I/O submit';
EVENT TOTAL_WAITS TIME_WAITED_MICRO
---------------------------------------------------------------- ----------- -----------------
db file async I/O submit 1944 88188121
[email protected]> set timing on;
[email protected]> update gyj100 set id=id+0 where rownum<=5000000;
5000000 rows updated.
Elapsed: 00:00:46.10
[email protected]> select event,TOTAL_WAITS , TIME_WAITED_MICRO from V$SYSTEM_EVENT where EVENT='db file async I/O submit';
EVENT TOTAL_WAITS TIME_WAITED_MICRO
---------------------------------------------------------------- ----------- -----------------
db file async I/O submit 2222 128007271
[email protected]> select (2222-1944)/46||'次/秒' from dual;
(2222-1944)/46
--------------
6.04347826次/秒
第二把测试，修改参数：
[email protected]> alter system set "_db_writer_coalesce_area_size"=8048576 scope=spfile;
System altered.
[email protected]> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
[email protected]> startup
ORACLE instance started.
Total System Global Area 388354048 bytes
Fixed Size 2228584 bytes
Variable Size 276827800 bytes
Database Buffers 104857600 bytes
Redo Buffers 4440064 bytes
Database mounted.
Database opened.
[email protected]> select event,TOTAL_WAITS , TIME_WAITED_MICRO from V$SYSTEM_EVENT where EVENT='db file async I/O submit';
no rows selected
[email protected]> update gyj100 set id=id+0 where rownum<=5000000;
5000000 rows updated.
Elapsed: 00:00:16.34
[email protected]> select event,TOTAL_WAITS , TIME_WAITED_MICRO from V$SYSTEM_EVENT where EVENT='db file async I/O submit';
EVENT TOTAL_WAITS TIME_WAITED_MICRO
---------------------------------------------------------------- ----------- -----------------
db file async I/O submit 31 15256544
[email protected]> select 31/16||'次/秒' from dual;
31/16
----------
1.9375次/秒
再测一把，把参数改回去：_db_writer_coalesce_area_size=1048576
[email protected]> alter system set "_db_writer_coalesce_area_size"=1048576 scope=spfile;
System altered.
[email protected]> startup force;
ORACLE instance started.
Total System Global Area 388354048 bytes
Fixed Size 2228584 bytes
Variable Size 276827800 bytes
Database Buffers 104857600 bytes
Redo Buffers 4440064 bytes
Database mounted.
Database opened.
[email protected]> select event,TOTAL_WAITS , TIME_WAITED_MICRO from V$SYSTEM_EVENT where EVENT='db file async I/O submit';
no rows selected
[email protected]> update gyj100 set id=id+0 where rownum<=5000000;
5000000 rows updated.
Elapsed: 00:00:48.49
[email protected]> [email protected]> select event,TOTAL_WAITS , TIME_WAITED_MICRO from V$SYSTEM_EVENT where EVENT='db file async I/O submit';
EVENT TOTAL_WAITS TIME_WAITED_MICRO
---------------------------------------------------------------- ----------- -----------------
db file async I/O submit 282 40353435
[email protected]> select 282/48||'次/秒' from dual;
282/48
----------
5.875次/秒
果然把参数db_writer_coalesce_area_size改大起作用了：
参数：_db_writer_coalesce_area_size=1048576， 产生db file async I/O submit等待6次/秒
参数：_db_writer_coalesce_area_size=8048576，产生db file async I/O submit等待2次/秒
转载于:https://blog.51cto.com/guoyjoe/1431339