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Posted to user@cassandra.apache.org by K F <kf...@yahoo.com> on 2016/03/09 17:23:53 UTC
ntpd clock sync
Hi,
I have question about ntpd. In certain clusters where new datacenters were added since 1 week we stood-up those machines didn't have ntpd running on them. Will it cause any problem if we enable or start ntpd now on those newly added datacenters.
Thanks.
Re: ntpd clock sync
Posted by Spencer Brown <li...@gmail.com>.
but what I'm saying is that every second will still hit. It's just that
that second will only last for 0.8s. So to the code above the OS and even
the shell level system calls, there is no difference. The difference is
very lo level - interrupts come in every micro-second or so from the CPU
and the OS just turns over the clock a little faster.
I've seen systems brought up to speed by days using NTP without problem -
it just takes a number of hours for the system to get where it needs to.
And if your system had been bleeding time, no files are post-dated... they
are all dated to something slightly behind the real time.
On Sat, Mar 12, 2016 at 3:35 PM, John Wong <go...@gmail.com> wrote:
> I believe K is asking whether he can sync up the clock now because he's
> concerned about losing data, as 30-40 seconds is pretty bad.
>
> On Sat, Mar 12, 2016 at 8:57 AM, Spencer Brown <li...@gmail.com>
> wrote:
>
>> NTP gradually speeds or slows the clock to arrive at actual time. So the
>> clock still hits every second but 1s may really be 0.8s or 1.2s. In your
>> case, it will sync up within a day. NTP is very clever so you never have
>> newer files back-dated to be older than older files or vice versa.
>>
>> Spencer
>>
>> On Thu, Mar 10, 2016 at 2:45 PM, Robert Coli <rc...@eventbrite.com>
>> wrote:
>>
>>> On Wed, Mar 9, 2016 at 9:03 AM, K F <kf...@yahoo.com> wrote:
>>>
>>>> the clock is about 30 to 40 seconds behind.
>>>>
>>>
>>> If you don't want to get ntp working there, why not just... manually...
>>> set the clocks?
>>>
>>> =Rob
>>>
>>
>>
>
Re: ntpd clock sync
Posted by John Wong <go...@gmail.com>.
I believe K is asking whether he can sync up the clock now because he's
concerned about losing data, as 30-40 seconds is pretty bad.
On Sat, Mar 12, 2016 at 8:57 AM, Spencer Brown <li...@gmail.com> wrote:
> NTP gradually speeds or slows the clock to arrive at actual time. So the
> clock still hits every second but 1s may really be 0.8s or 1.2s. In your
> case, it will sync up within a day. NTP is very clever so you never have
> newer files back-dated to be older than older files or vice versa.
>
> Spencer
>
> On Thu, Mar 10, 2016 at 2:45 PM, Robert Coli <rc...@eventbrite.com> wrote:
>
>> On Wed, Mar 9, 2016 at 9:03 AM, K F <kf...@yahoo.com> wrote:
>>
>>> the clock is about 30 to 40 seconds behind.
>>>
>>
>> If you don't want to get ntp working there, why not just... manually...
>> set the clocks?
>>
>> =Rob
>>
>
>
Re: ntpd clock sync
Posted by Spencer Brown <li...@gmail.com>.
NTP gradually speeds or slows the clock to arrive at actual time. So the
clock still hits every second but 1s may really be 0.8s or 1.2s. In your
case, it will sync up within a day. NTP is very clever so you never have
newer files back-dated to be older than older files or vice versa.
Spencer
On Thu, Mar 10, 2016 at 2:45 PM, Robert Coli <rc...@eventbrite.com> wrote:
> On Wed, Mar 9, 2016 at 9:03 AM, K F <kf...@yahoo.com> wrote:
>
>> the clock is about 30 to 40 seconds behind.
>>
>
> If you don't want to get ntp working there, why not just... manually...
> set the clocks?
>
> =Rob
>
Re: ntpd clock sync
Posted by Robert Coli <rc...@eventbrite.com>.
On Wed, Mar 9, 2016 at 9:03 AM, K F <kf...@yahoo.com> wrote:
> the clock is about 30 to 40 seconds behind.
>
If you don't want to get ntp working there, why not just... manually... set
the clocks?
=Rob
Re: ntpd clock sync
Posted by K F <kf...@yahoo.com>.
the clock is about 30 to 40 seconds behind.
From: Jack Krupansky <ja...@gmail.com>
To: user@cassandra.apache.org
Sent: Wednesday, March 9, 2016 11:31 AM
Subject: Re: ntpd clock sync
How far out of sync are the nodes? A few minutes or less? Many hours?
Worst case, you could simply take the entire cluster down until that future time has passed and then bring it back up.
-- Jack Krupansky
On Wed, Mar 9, 2016 at 11:27 AM, Jeff Jirsa <je...@crowdstrike.com> wrote:
If you don’t overwrite or delete data, it’s not a concern.If the clocks show a time in the past instead of in the future, it’s not a concern.
If the clock has drifted significantly into the future, when you start NTP you may be writing data with timestamps lower than timestamps on data that already exists. In this case, the existing data (with timestamps in the future) may take precedence over new writes (with correct timestamps).
From: K F
Reply-To: "user@cassandra.apache.org", K F
Date: Wednesday, March 9, 2016 at 8:23 AM
To: User
Subject: ntpd clock sync
Hi,
I have question about ntpd. In certain clusters where new datacenters were added since 1 week we stood-up those machines didn't have ntpd running on them. Will it cause any problem if we enable or start ntpd now on those newly added datacenters.
Thanks.
Re: ntpd clock sync
Posted by Jack Krupansky <ja...@gmail.com>.
How far out of sync are the nodes? A few minutes or less? Many hours?
Worst case, you could simply take the entire cluster down until that future
time has passed and then bring it back up.
-- Jack Krupansky
On Wed, Mar 9, 2016 at 11:27 AM, Jeff Jirsa <je...@crowdstrike.com>
wrote:
> If you don’t overwrite or delete data, it’s not a concern.
> If the clocks show a time in the past instead of in the future, it’s not a
> concern.
>
> If the clock has drifted significantly into the future, when you start NTP
> you may be writing data with timestamps lower than timestamps on data that
> already exists. In this case, the existing data (with timestamps in the
> future) may take precedence over new writes (with correct timestamps).
>
>
>
> From: K F
> Reply-To: "user@cassandra.apache.org", K F
> Date: Wednesday, March 9, 2016 at 8:23 AM
> To: User
> Subject: ntpd clock sync
>
> Hi,
>
> I have question about ntpd. In certain clusters where new datacenters were
> added since 1 week we stood-up those machines didn't have ntpd running on
> them. Will it cause any problem if we enable or start ntpd now on those
> newly added datacenters.
>
> Thanks.
>
Re: ntpd clock sync
Posted by Jeff Jirsa <je...@crowdstrike.com>.
If you don’t overwrite or delete data, it’s not a concern.
If the clocks show a time in the past instead of in the future, it’s not a concern.
If the clock has drifted significantly into the future, when you start NTP you may be writing data with timestamps lower than timestamps on data that already exists. In this case, the existing data (with timestamps in the future) may take precedence over new writes (with correct timestamps).
From: K F
Reply-To: "user@cassandra.apache.org", K F
Date: Wednesday, March 9, 2016 at 8:23 AM
To: User
Subject: ntpd clock sync
Hi,
I have question about ntpd. In certain clusters where new datacenters were added since 1 week we stood-up those machines didn't have ntpd running on them. Will it cause any problem if we enable or start ntpd now on those newly added datacenters.
Thanks.