topic Re: synchronizing time in Operating System - OpenVMS

synchronizing time

Lokesh_2 — Fri, 02 Jul 2004 07:39:29 GMT

Hi,

Which is best to synchronize time between nodes of a cluster ? Or all are same ? I want to know the difference between following command if any .

1. Set time/cluster

2. MC SYSTEM SET ENV/CLU
SET PROFILE/PRIVILEGE=(LOG_IO,SYSLCK)
DO SET TIME

3. MC SYSMAN SET ENV/CLU
SET PROFILE/PRIVILEGE=(LOG_IO,SYSLCK)
CONFIG SET TIME

Thanks & regards,
Lokesh

P.S. I know about DTSS & NTP, but right now don't want to use them. Instead , will make DCL procdure which will use any of the above command to run on regular basis.

Re: synchronizing time

labadie_1 — Fri, 02 Jul 2004 07:43:40 GMT

I do not know which is best, I think they all work.

I have use 3 (config set time) quite often without aby problem.

Re: synchronizing time

Ian Miller. — Fri, 02 Jul 2004 07:44:14 GMT

I think they have the same affect. Read the clock on this system and set the clock on all nodes to be the same.

Re: synchronizing time

Lokesh_2 — Fri, 02 Jul 2004 07:50:40 GMT

Hi,

As per documentation:-

"SYSMAN tries to ensure that all processors in the cluster are set to the same time. Because of communication and processing delays, it is not possible to synchronize clocks exactly. However, the variation is typically less than a few hundredths of a second. If SYSMAN cannot set the time to within one-half second of the specified time, you receive a warning message that names the node that failed to respond quickly enough."

So this explain about SYSMAN . How does SET TIME/CLUSTER work ?

Thanks & regards,
Lokesh

Re: synchronizing time

Kris Clippeleyr — Fri, 02 Jul 2004 09:11:32 GMT

Lokesh,

Be careful when using the SYSMAN option CONFIG SET TIME. Although the "one half second difference" is checked, the clock on some systems can go backward. I've worked on a site where this "feature" had disastrous consequences.

Greetz,

Kris

Re: synchronizing time

Lokesh_2 — Fri, 02 Jul 2004 09:27:57 GMT

Hi Kris,

Was your site consists of Alpha or VAX ? What was the reasond found ?

Thanks & regards,
Lokesh

Re: synchronizing time

Kris Clippeleyr — Fri, 02 Jul 2004 09:32:53 GMT

Lokesh,

The site I've worked used mainly Alphas for there clusters.
The "disastrous" consequences I talked about were caused by an application that heavily relied on the system clock. The application simply couldn't stand the system time going backward (not even by half a second). The application crashed, and we had quite a job to restart it & repair the damage.

Sorry, I can't go into further detail (you know: non-disclosure)

Greetz,

Kris

Re: synchronizing time

Amit Levin_2 — Sat, 03 Jul 2004 09:37:27 GMT

Hi Lokesh,
I use NTP in my site.
Its biggest advantage is that it does'nt make your clock "jump". It either slows it or make it work faster until the time in the NTP client is equal to the time in the NTP server.

Re: synchronizing time

Anthony Fiorito — Sun, 04 Jul 2004 10:05:28 GMT

Lokesh,

I'm with Kris. You really want to use NTP or DTSS. I've had very bad experiences with a DSM application that bellied-up if a clock went backwards, even just a tiny bit. Until the advent of NTP, that site used to actually shutdown their application a couple of times a year so that clocks could be reset and synchronized.

Anthony Fiorito

Re: synchronizing time

Lokesh_2 — Mon, 05 Jul 2004 02:54:55 GMT

Hi All,

Thanks for your inputs.

Best regards,
Lokesh Jain

Re: synchronizing time

Anton van Ruitenbeek — Mon, 05 Jul 2004 04:02:02 GMT

Hi,

In a cluster you need to use MC SYSMAN/CONFIG SET TIME . This because the DO SET TIME has always an interleave between the executing nodes.
The time backward/foreward cannot be omitted. Just because there can be a time difference.
If you don't want any trouble: use DTSS. Because this modificates the clockspeed to move slowly to the needed time. So the time won't be set directly back if needed, but the internal clock is slowing till the moment it needes. NTP tries to do the same, only ..nix style :-(.

AvR

Re: synchronizing time

Jayshankar K J — Mon, 05 Jul 2004 07:05:52 GMT

Hi Lokesh,

The reason why we can't set the time backwards, only because application updates the databases with time stamps and this happen every time whenever there is an insert, delete or update is happening. And whenever we try to take the system time backwards, application crashes due to mismatch in the time stamps and it is very severe as far as online systems are concerned

warm regards
shankar