（先确保要event的会话环境符合条件）
1、必须确保timed_statistics为true，这个参数可以在会话级上进行修改。
关于参数timed_statistics的一段解释
without timed statistics, oracle records the reason for each wait before it begins to wait, and when the wait is over, it records whether it timed out. but with timed statistics enabled, oracle checks the time just before and after each wait, and also records the time waited. the time waited is recorded in hundredths of a second— that is, centiseconds.
true
the statistics are collected and stored in trace files or displayed in the v$sesstats and v$sysstats dynamic performance views.
false
the value of all time-related statistics is set to zero. this setting lets oracle avoid the overhead of requesting the time from the operating system.
starting with release 11.1.0.7.0, the value of the timed_statistics parameter cannot be set to false if the value of statistics_level is set to typical or all.
与sql trace相关的参数
在打开10046时间的sql trace之前，要先设置好下面几个参数。
timed_statistics
这个参数决定了是否收集与时间相关的统计信息，如果这个参数为false的话，那么sql trace的结果基本没有多大的用处，默认情况下这个参数设置为true。
max_dump_file_size
dump文件的大小，也就是决定是否限制sql trace文件的大小，在一个很忙的系统上面做sql trace的话可能会生成很多的信息，因此最好在会话级别将这个参数设置成unlimited。
tracefile_identifier
给trace文件设置识别字符串，这是个非常有用的参数，设置一个易读的字串能更快的找到trace文件。
要在当前会话修改上述参数很简单，只要使用下面的命令即可：
alter session set timed_statistics=truealter session set max_dump_file_size=unlimitedalter session set tracefile_identifier='my_trace_session
当然，这些参数可以在系统级别修改的，也可以加载init文件中或是spfile中，让系统启动时自动做全局设置。
要是在系统运行时动态的修改别的会话的这些参数就需要借助dbms_system这个包了，设置方法如下
sys.dbms_system.set_bool_param_in_session( :sid, :serial, 'timed_statistics', true) sys.dbms_system.set_int_param_in_session( :sid, :serial, 'max_dump_file_size', 2147483647)案例：
13:55:30 sys@ prod >select username,sid,serial# from v$session where username is not null;username sid serial#------------------------------ ---------- ----------sys 1 5scott 40 587sys 48 56914:31:33 sys@ prod >desc dbms_systemprocedure add_parameter_value argument name type in/out default? ------------------------------ ----------------------- ------ -------- parname varchar2 in value varchar2 in scope varchar2 in default sid varchar2 in default position binary_integer in defaultprocedure dist_txn_sync argument name type in/out default? ------------------------------ ----------------------- ------ -------- inst_num number inprocedure get_env argument name type in/out default? ------------------------------ ----------------------- ------ -------- var varchar2 in val varchar2 outprocedure kcfrmsprocedure ksdddtprocedure ksdflsprocedure ksdind argument name type in/out default? ------------------------------ ----------------------- ------ -------- lvl binary_integer inprocedure ksdwrt argument name type in/out default? ------------------------------ ----------------------- ------ -------- dest binary_integer in tst varchar2 inprocedure read_ev argument name type in/out default? ------------------------------ ----------------------- ------ -------- iev binary_integer in oev binary_integer outprocedure remove_parameter_value argument name type in/out default? ------------------------------ ----------------------- ------ -------- parname varchar2 in value varchar2 in scope varchar2 in default sid varchar2 in defaultprocedure remove_parameter_value argument name type in/out default? ------------------------------ ----------------------- ------ -------- parname varchar2 in position binary_integer in scope varchar2 in default sid varchar2 in defaultprocedure set_bool_param_in_session argument name type in/out default? ------------------------------ ----------------------- ------ -------- sid number in serial# number in parnam varchar2 in bval boolean inprocedure set_ev argument name type in/out default? ------------------------------ ----------------------- ------ -------- si binary_integer in se binary_integer in ev binary_integer in le binary_integer in nm varchar2 inprocedure set_int_param_in_session argument name type in/out default? ------------------------------ ----------------------- ------ -------- sid number in serial# number in parnam varchar2 in intval binary_integer inprocedure set_sql_trace_in_session argument name type in/out default? ------------------------------ ----------------------- ------ -------- sid number in serial# number in sql_trace boolean inprocedure wait_for_event argument name type in/out default? ------------------------------ ----------------------- ------ -------- event varchar2 in extended_id binary_integer in timeout binary_integer in 14:28:02 sys@ prod >exec dbms_system.set_bool_param_in_session(40,587,'time_statistics',true);pl/sql procedure successfully completed.14:33:59 sys@ prod >exec dbms_system.set_int_param_in_session(40,587,'max_dump_file_size',2147364847);pl/sql procedure successfully completed.10046 trace启动方法