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Well, not quite. a) suddenly the clients see themselves as going too fast. It
will take a while to realise that, and then a while to get their clocks up to
speed, and then a few minutes later they see themselves as going to slow so
the whole palaver goes again. During that time they are out even more from UTC
that are the servers. And if they have settled down to querying the server
only every couple of hours that whole thing will take place well after
midnight.
And if those clients are using some server as well or are using a leapsecond
file, they will thing that at midnight UTC (and the servers serving UTC) there
will be a discontinuity, they will also try to compensate for that, and get
even more messed up. And if they are acting as servers for other machines
those other machines will get even more messed up. So it could take a day or
days for all the machines back to marching to UTC again.
William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1 ____|____ and Gravity ______|_ www.theory.physics.ubc.ca/
On Fri, 10 Apr 2020, Hal Murray wrote:
Lars-Daniel.Weber@xxxxxx said:
So for logging on a webserver (with database and stuff), you'd recommend to
use Holger's settings?
You are missing the big picture.
The idea is that if you are a company like Google with zillions of database
servers that you want to run on smeared time, you setup the few NTP servers at
the top of your NTP tree to give out smeared time. Then you don't have to
change anything on your internal NTP servers or database servers. They don't
know they are running on smeared time. They just follow the time from the top
NTP servers.
(I'm using the term "database servers" to distinguish them from NTP servers.)
If you want your systems to run on smeared time, there are two approaches.
You can point all your internal systems running NTP at external smearing
servers. Google and Facebook run public smearing NTP servers. I don't know
of any others. That works if you have only a few systems. Just point them
all at smearing servers.
If you have enough database servers in your system, you probably have an
internal NTP tree and a few NTP servers at the top. You can point those top
NTP servers at non-smearing servers and set them up to give out smeared time.
If you do that, you probably don't want to run anything else on those top
boxes. They will be running on true time which will be offset from the time
on the rest of your machines while a smear is in progress so log files won't
match up.
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A key idea is that a NTP server should point to either all smearing or all
non-smearing servers, not a mix.
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If you do run a system (NTP or database) on smeared time, you need to make
sure that you don't tell it about the leap file.
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