Oracle Warning: VKTM detected a time drift.

jiawang

在MOS中，定位到了一篇针对alert log中出现Time Drift提示错误的文章，名称为：Time Drift Detected. Please Check VKTM Trace File for More Details，文章编号：ID 1347586.1。
  在文章中，Oracle认为这个错误在11.2.0.2到11.2.0.3之间会不断地出现，已经在11.2.0.4版本中被修复。Bug编号为：11837095 "TIME DRIFT DETECTED" APPEARS INTERMITTENTLY IN ALERT LOG, THO' EVENT 10795 SET。
  如果需要对该Bug进行单独修复，需要进行补丁patch 11837095操作。之后通过设置等待事件10795来进行控制。
  alter system set event="10795 trace name context forever, level 2" scope=spfile;
  这种错误的潜在影响，MOS文章中的解释如下：
  Impact of the error:
  The time drifts usually occurring less than 1sec and 5 sec for forward and backward respectively are permissible and OK.
  If the traces are emitting time drifts of amount beyond these ranges, then it needs to be analyzed.
  Most of the times, during high loads, there would be issues with underlying OS due to virtual memory, network time protocol improper configuration etc.
  In general VKTM process need to be scheduled in every 10ms, if due to above reasons this is not happening we see the time drifts and to certain level (mentioned above) are permissible.
  Eventually, this probably would cause the resource manager to take improper decisions and can lead to a hang in worst case.
  VKTM process trace file can be found under bdump, However in this case the trace file doesn't contain useful information, Which makes the message ambiguous.
  大部分情况下，由于系统高负载或者内存调度配置有问题，VKTM的每10ms作业会有问题，可能会出现1-5秒的Drift漂移。如果这种现象出现很频繁，就需要整体考虑操作系统和数据库配置问题。
VKTM出现漂移，可能会影响到resource manager的工作情况。
  3、结论
  VKTM是Oracle 11g中新引入的一个后台进程。我们在面对alert log中出现的各种奇怪问题的时候，最好主动咨询一下官方MOS，看看是否有相似的方案解决。小问题尽早解决，才能保证系统不出现大故障。