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Today I will show you how to analyze Oracle RAC time synchronization. The content of the article is good. Now I would like to share it with you. Friends who feel in need can understand it. I hope it will be helpful to you. Let's read it along with the editor's ideas.

1.RAC related time synchronization (time synchronization)

Oracle Grid can synchronize time in two ways

1) NTP based on OS

2) CTSS based on clusterware (Cluster Time Synchronization Service)

When installing and configuring RAC, you can only choose one of the above two synchronization methods. If NTP is selected, CTSS will be in observation mode (Observer Mode); if CTSS is selected, NTP,CTSS will be in active mode (active mode) must be disabled

Time synchronization will take place between cluster nodes without contacting external servers.

two。 Specific methods of selecting CTSS and disabling NTP

# / sbin/service ntpd stop-stop the ntp service

# chkconfig ntpd off-disable ntp service boot

# rm / etc/ntp.conf (or mv / etc/ntp.conf to / etc/ntp.conf.bk)-Delete the ntp configuration file

And remove the following files

# rm-f / var/run/ntpd.pid-delete the ntpd.pid file (which saves the pid of the ntp service daemon)

View the mode of the CTSS process

# crsctl check ctss

CRS-4701: The Cluster Time Synchronization Service is in Active mode.

CRS-4702: Offset (in msec): 0

3. Adopt ntp mode

Configure-x identity for ntpd, modify / etc/sysconfig/ntpd

# Drop root to id 'ntp:ntp' by default.

PTIONS= "- x-u ntp:ntp-p / var/run/ntpd.pid"

# Set to 'yes' to sync hw clock after successful ntpdate

SYNC_HWCLOCK=no

# Additional options for ntpdate

NTPDATE_OPTIONS= ""

Then, restart the NTP service.

Restart the ntp service

# / sbin/service ntp restart

4. Instructions on NTP synchronization method

There are two ways to NTP:

1) Manual ntpdate (via crontab): this method is characterized by one adjustment in place.

2) automatic adjustment through ntpd service

Ntpd service adjustment strategy is divided into gradual adjustment (fine tuning, slewing time) and jump adjustment. The difference between the two is that the former adds the "- x" (slew) parameter when starting the NTP service, but does not add the "- x" parameter by default.

The disadvantage of adding "- x" parameter is that when the time difference is large, the synchronization takes a long time. At the same time, both strategies have a corresponding threshold (threshold), and once exceeded, a jump will occur.

If you do not add "- x", the threshold is 128s, less than 128s, step by step adjustment, greater than, jump adjustment; add "x" threshold is 600s, less than 600s, gradual adjustment, greater than, jump adjustment.

When the threshold exceeds 1000s under both policies, ntpd stops and the parameter "- g" is ignored.

5. The effect of using NTP plus the "- x" parameter (Linux/Unix)

Without the "- x" parameter, NTP adjusts the system time forward or backward when the time difference exceeds a specific (depending on the platform) threshold. Adjusting the time significantly backward will cause Clusterware to mistakenly think that check-in has been missed, which leads to node expulsion. Therefore, it is recommended to add a "- x" parameter to NTP.

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