[bind10-dev] 转发: Should zonemgr refresh expired zones(Re: zonemgr / notify out questions)

[Shane Kerr]

On Tue, 2010-09-14 at 16:57 +0800, Likun Zhang wrote: 
> > I see there as being two alternatives.  If "r" is the refresh time and "j"
> the jitter
> > value we could set it that the zone refreshes:
> > 
> > a) any time between r - j and r
> > 
> > or
> > 
> > b) any time between r - j and r + j
> > 
> > My own thought is that the latter is the most natural definition, as the
> term jitter
> > tends to imply a deviation about a mean.
> 
> Yeah, from the mean of jitter, the latter one is more natural, but my
> concern is, it will delay zone refresh which may not user wants,
> 
> Like a meeting or check in time of company, we can arrive ahead or in time,
> if you are late, what the boss will say? 

I think if we use (r-j, r) as the range of the first time selected, then
use r for any following refresh times, we would meet the goals of not
overloading servers and also giving maximal predictability to the server
behavior.

Details...


Since the point of jitter in refresh is to avoid having all of the zones
slaved by a server refreshed at the same time, we only need jitter for
the first refresh of any given zone. 

For example, if we have 3 zones that are set to refresh after 600
seconds, and jitter puts one at 500 seconds, one at 550 seconds, and one
at 600 seconds, we can then use the "real" refresh timer after that. So
for the first zone it would be 500, then 1100, then 1700, and so on. For
the second zone it would be 550, then 1150, then 1750, and so on.

This allows us to solve the problem of having everything get refreshed
at the same time, and also sets the refresh timer as close to what
whoever set up the SOA specified (once the first refresh has passed).

This does not completely address the problem of what happens for the
first jitter. We could pick (r-j, r+j) as the range, but I agree that it
seems like a problem if the refresh time passes without a refresh that
this seems like an error to administrators.

Note that this will seem less like a problem when we are able to list
all of the zones along with their refresh and expiry times:


<=BINDCTL PROMPT=> list slave zones
Zone                Status  Zone Activity Next Refresh  Expiry
------------------- ------  ------------- ------------- ------
EXAMPLE.COM         okay    none                  4m03s 2010-09-14 15:12:11
TIME-TRAVELLERS.ORG okay    refreshing               0s 2010-09-21 17:33:12
ISC.ORG             EXPIRED waiting            2h17m34s n/a
中国.CN              okay    none           13d23h52m11s 2010-10-02 03:13:11

I think this will be less of a problem if administrators can see what is
going on, because they won't have to worry if something is broken.
Hopefully. :)

--
Shane