RE: os date, sysdate & time synchronization

Oracle does keep track of time in v$timer but its implementation eludes me. However, the implementation probably doesn't matter because of the manner in which ntpd (or xntpd) changes the system clock. See RFC1305 for more information on what's called the Fuzzball Implementation. It basically states that ntpd will gradually adjust the system clock until it 'matches' its master(s).  

When your host restarts you will probably want to execute (in /etc/init.d/ntpd) ntpd with a -g argument so that it will initially set the system clock to its master's clock regardless of how far its own clock has drifted. Then, from that point forward, ntpd will impose only tiny adjustments.  

The reason I mention this is so that you can feel more comfortable about measuring time in units larger than milliseconds. If you wish to measure time in milliseconds or microseconds while ntpd is changing the clock, then be prepared to get goofy data. The good news is that you're not likely to get more than one or two consecutive goofy data points because ntpd can implement tiny adjustments very quickly. If ntpd were constantly changing the clock then that would mess things up (but there would be a bug fix on the web in no time short if it happened). The extremely good news is that you probably don't have an application that cares about short time intervals (e.g., less than 5,000 microseconds). Sure, it's possible that Oracle might occasionally register a wait event that was slightly smaller or larger (1cs) than reality but that would matter only if the number of wait events were very small. When we perceive a wait event related performance problem it's either because the event lasted a long time (seconds) and/or there were many of them. Why would you attack a single wait event that registered as, say, 3cs instead of 2cs?
Jeff Holt

Hotsos Enterprises, Ltd.
http://www.hotsos.com

Upcoming events:
- Hotsos Clinic <http://www.hotsos.com/training/clinic> , Oct 1-3 San
Francisco, Oct 15-17 Dallas, Dec 9-11 Honolulu
- 2003 Hotsos Symposium <http://www.hotsos.com/events/symposium> on
OracleR System Performance, Feb 9-12 Dallas
- Next event: Miracle Database Forum <http://www.miracleas.dk> , Sep
20-22 Middlefart Denmark
-----Original Message-----
Richard
Sent: Tue, Aug 27, 2002 17:19
To: Multiple recipients of list ORACLE-L  

I am considering ntpd to synchronize my server times but I wanted to check if there are any issues with actively synchronizing the system time when there is an oracle database involved. Does the db maintain its own time clock after its started so that the timestamps in the control file are not affected by outside adjustments? I am curious of what anyone had had to deal with or consider in this type of scenario. TIA for any information.

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Jeff Holt
  INET: jeff.holt_at_hotsos.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).