Oracle 9i,10g,11gR1基於Linux的RAC都需要Hangcheck-Timer模組

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Hangcheck-Timer Module Requirements for Oracle 9i, 10g, and 11g RAC on Linux

Starting in release 9.2.0.2 and later, Oracle RAC environments required using a new I/O fencing model, named the hangcheck-timer module. This module was implemented to replace the Watchdog module, which provided similar fencing functionality. Hangcheck-timer was subsequently delivered as part of the standard kernel distribution for Linux kernel releases 2.4 and above. 

Hangcheck-timer should be loaded at boot time, and monitors the Linux kernel for long operating system hangs that could affect the reliability of a RAC node.  It runs in kernel mode and uses the Time Stamp Counter (TSC) to catch scheduling delays or node hangs.  This is done by setting a timer, then checking when the timer fires as to whether it was delayed by more than the allowed margin of error.  If the duration exceeds the allowed time of (hangcheck_tick + hangcheck_margin seconds), the machine is restarted.  Hangcheck-timer will not cause reboots to occur due to CPU starvation.

 Hangcheck-timer requires three configuration parameters:

• hangcheck_tick - defines how often, in seconds, the hangcheck-timer checks the node for hangs. The default value is 60 seconds.
• hangcheck_margin - defines how much margin is allowed, in seconds, between expected scheduling and real scheduling time. The default value is 180 seconds.
• hangcheck_reboot - determines if the hangcheck-timer restarts the node if the kernel fails to respond within the sum of the hangcheck_tick and hangcheck_margin parameter values. If the value of hangcheck_reboot is equal to or greater than 1, then the hangcheck-timer module restarts the system. If the hangcheck_reboot parameter is set to zero, then the hangcheck-timer module will not reboot the node, even if a hang is detected.   The default value varies by kernel version.  In the 2.4 kernel, the default is 1.  In 2.6 kernels, the default is 0.

• 9i: Assuming the default setting of "oracm misscount" is set to 220 seconds: 
  hangcheck_tick=30 hangcheck_margin=180 hangcheck_reboot=1
• 10g/11g: Assuming the default setting of "CSS misscount" is set to either 30 or 60 seconds:
  hangcheck_tick=1 hangcheck_margin=10 hangcheck_reboot=1

You must always ensure that the Cluster misscount setting is greater than the sum of the setting for hangcheck_tick + hangcheck_margin. 

@  Unpublished information for Oracle Support Internal Use: 

When running Oracle Clusterware on Linux, hangcheck-timer should always be configured on each RAC cluster node, as the functionality of this module is required to provide I/O Fencing to ensure no stray writes will occur from an evicted node in a RAC cluster.  To verify if the hangcheck-timer module is running on a node execute as the root or oracle user: