1 Warning: VKTM detected a time drift. 2 Time drifts can result in an unexpected behavior such as time-outs. Please check trace file for more details. 3 Tue Dec 03 16:21:35 2019 4 Warning: VKTM detected a time drift. 5 Time drifts can result in an unexpected behavior such as time-outs. Please check trace file for more details. 6 Tue Dec 03 16:38:23 2019 7 Adjusting the default value of parameter parallel_max_servers 8 from 640 to 320 due to the value of parameter processes (350) 9 Starting ORACLE instance (normal) 10 Tue Dec 03 21:09:32 2019 11 Warning: VKTM detected a time drift. 12 Time drifts can result in an unexpected behavior such as time-outs. Please check trace file for more details. 13 Tue Dec 03 22:00:00 2019 14 Setting Resource Manager plan SCHEDULER[0x32DA]:DEFAULT_MAINTENANCE_PLAN via scheduler window 15 Setting Resource Manager plan DEFAULT_MAINTENANCE_PLAN via parameter 16 Tue Dec 03 22:00:00 2019 17 Starting background process VKRM 18 Tue Dec 03 22:00:00 2019 19 VKRM started with pid=78, OS id=28922 20 Tue Dec 03 22:00:02 2019 21 Begin automatic SQL Tuning Advisor run for special tuning task "SYS_AUTO_SQL_TUNING_TASK" 22 Tue Dec 03 22:20:55 2019 23 End automatic SQL Tuning Advisor run for special tuning task "SYS_AUTO_SQL_TUNING_TASK" 24 Tue Dec 03 22:46:17 2019 25 Warning: VKTM detected a time drift. 26 Time drifts can result in an unexpected behavior such as time-outs. Please check trace file for more details. 27 Wed Dec 04 00:00:29 2019 28 Thread 1 advanced to log sequence 5843 (LGWR switch)
在Oracle Database 11g中，VKTM是一个新增的后台进程。这个进程的含义是：
VKTM (virtual keeper of time) is responsible for providing a wall-clock time (updated every second) and
reference-time counter (updated every 20 ms and available only when running at elevated priority).
也就是说，这个进程用于提供一个数据库的时钟，每秒更新；或者作为参考时间计数器，这种方式每20毫秒更新一次，仅在高优先级时可用。
在系统时间出现异常或变化时，VKTM进程还会检测这些变化，提醒用户，尤其是在RAC环境中，时间的偏移和变化极有可能导致系统故障。以下是告警日志中的警告信息：
Warning: VKTM detected a time drift.
Time drifts can result in an unexpected behavior such as time-outs. Please check trace file for more details.
通过VKTM进程，数据库可以降低和操作系统的交互，Kamus的解释是：
在11g之前所有的Oracle数据库后台或者前台进程如果需要获得当前时间信息，就需要调用操作系统的gettimeofday()函数或者说是相类似的函数。
而VKTM进程就是专门用来获得时间信息然后将信息存放在SGA中供其它进程使用，这样其它进程当需要时间信息的时候，只要到SGA的某个内存位置去获得就好，
而不用频繁调用gettimeofday()函数。毫无疑问，这样效率会更高。
在RAC测试中，Oracle 11.1.0.6版本LMSx进程获取时间信息时，可以从VKTM进程中获益大概70%的速度提升，而11.1.0.7将会更高。
同时，因为gettimeofday()函数也引发了很多bug，所以无论是RAC还是NORAC库，都将从VKTM进程中获益。
参考
https://www.eygle.com/archives/2012/06/oracle_11g_vktm.html
Warning: VKTM detected a time drift.
原文：https://www.cnblogs.com/yunweiyipai/p/13098308.html