Re: buildfarm animals and 'snapshot too old'

On 05/20/2014 03:59 PM, Gavin Flower wrote:
> On 21/05/14 01:42, Tom Lane wrote:
>> Andrew Dunstan<andrew@dunslane.net>  writes:
>>> On 05/20/2014 07:09 AM, Tom Lane wrote:
>>>> Robert's got a point here.  In my usage, the annoying thing is not animals
>>>> that take a long time to report in; it's the ones that lie about the
>>>> snapshot time (which is how you get "512abc4 in the middle of a bunch of
>>>> ef9ab5f's").  That is an issue of incorrect system clock, not of how long
>>>> it takes to do the run.  I wonder if the buildfarm script could be taught
>>>> to get the timestamp from an NTP server somewhere?  Or at least
>>>> sanity-check the system clock reading by comparing it to the newest commit
>>>> timestamp in the git repo.
>>> Regarding clock skew, I think we can do better then what you suggest.
>>> The web transaction code in the client adds its own timestamp just
>>> before running the web transaction. It would be quite reasonable to
>>> reject reports from machines with skewed clocks based on this value. I'm
>>> not sure what a reasonable skew might be. Somewhere in the range of 5 to
>>> 15 minutes seems reasonable.
>> Rather than reject, why not take the result and adjust the claimed start
>> timestamp by the difference between the web transaction timestamp and the
>> buildfarm server's time?
>>
>>             
>>
> I think, that if possible, any such adjustment should be noted along 
> with the original time, so that:
>
>  1. the timing issue can be remedied
>  2. it is possible to link the output to any messages in the machines
>     log etc.
>


I don't see how that's going to help anyone. Major clock skew is a sign 
of client misconfiguration. And where would we note this adjustment, and 
who would do anything about it?

We seem to be engaging in a sort of PoohBearism* here. More information 
is not always better.

cheers

andrew



*    Rabbit: Would you like *condensed milk*, or *honey* on your bread?    Winnie the Pooh: Both. But never mind the
bread,please.