Writes

Support for COMMIT_WAIT is experimental and requires careful tuning of the time-synchronization protocol, such as NTP (Network Time Protocol). Its use in production environments is discouraged.

Recommendation

If external consistency is a requirement and you decide to use COMMIT_WAIT, the time-synchronization protocol needs to be tuned carefully. Each transaction will wait 2x the maximum clock error at the time of execution, which is usually in the 100 msec. to 1 sec. range with the default settings, maybe more. Thus, transactions would take at least 200 msec. to 2 sec. to complete when using the default settings and may even time out.

• A local server should be used as a time server. We have performed experiments using the default NTP time source available in a Google Compute Engine data center and were able to obtain a reasonable tight max error bound, usually varying between 12-17 milliseconds.

• The following parameters should be adjusted in /etc/ntp.conf to tighten the maximum error:

  • server my_server.org iburst minpoll 1 maxpoll 8

  • tinker dispersion 500

  • tinker allan 0