SQL SELECT * FROM v$version; BANNER ---------------------------------------------------------------- Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - Prod PL/SQL Release 10.2.0.3.0 - Production SQL select name,parameter1,paramet SQL> SELECT * FROM v$version; BANNER ---------------------------------------------------------------- Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - ProdPL/SQL Release 10.2.0.3.0 - Production SQL>SELECT name,parameter1,parameter2,parameter3,wait_class from v$event_name 2 where name in ('free buffer waits','db file parallel write','write complete waits'); NAME PARAMETER1 PARAMETER2 PARAMETER3 WAIT_CLASS ------------------------- ---------- ---------- ---------- ------------------------------ free buffer waits file# block# set-id# Configurationwrite complete waits file# block# Configurationdb file parallel write requests interrupt timeout System I/O 在Oracle 10g中，db file parallel write 被归属为系统I/0等待类，如果你检查到了系统出现了大量的 db file parallel write事件，表明你的I/O有问题。这时你可以检查 db file parallel write ，write complete waits，free buffer waits的平均等待时间 SQL> select event,time_waited,average_wait from v$system_event where event in 2 ('db file parallel write','write complete waits','free buffer waits'); EVENT TIME_WAITED AVERAGE_WAIT ---------------------------------------------------------------- ----------- ------------ db file parallel write 284 .67
我这里由于是测试机器，没有出现 write complete waits,free buffer waits 等待事件
AVERAGE_WAIT的值应该小于1(百分之一秒)，如果AVERAGE_WAIT大于10（十分之一秒）,表明非常缓慢的I/O，出现了db file parallel write 时常也会伴随write complete waits等待，如果是非常繁忙的OLTP系统，还可能出现free buffer waits，因为缓慢的I/0势必影响前台进程。db file parallel write只属于DBWR进程独有，不要被名字迷惑了，不要误解为该事件与并行DML有关。
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