等待事件-log file single write



log file single write 

该事件仅与写日志文件头块相关，通常发生在增加新的组成员和增进序列号（ log switch）

时。头块写单个进行，因为头块的部分信息是文件号，每个文件不同。

更新日志文件头这个操作在后台完成，一般很少出现等待，无需太多关注。在 log switch

的过程中， LGWR 需要改写日志文件头，有时可以观察到该等待事件的增加：

SQL> select event,time_waited from v$system_event where event='log file single write';

EVENT TIME_WAITED

---------------------------------------------------------------- -----------

log file single write 2848

SQL> alter system switch logfile;

System altered.

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SQL> alter system switch logfile;

System altered.

SQL> select event,time_waited from v$system_event where event='log file single write';

EVENT TIME_WAITED

---------------------------------------------------------------- -----------

log file single write 2853

SQL> alter system switch logfile;

System altered.

SQL> select event,time_waited from v$system_event where event='log file single write';

EVENT TIME_WAITED

---------------------------------------------------------------- -----------

log file single write 2855