Re: [vserver] start-vservers patch

Jeff Jansen wrote:
> On Tuesday 01,February,2011 02:03 PM, Daniel Hokka Zakrisson wrote:
>> Why aren't you just using the depends file to specify dependencies?
>
> As I understand it, using the 'depends' files either mean you start all
> your vservers one at a time, or you start them in groups of X number at
> a time, but you can't control the order within that group. Worse, you
> may wait until a whole group of X is finished before starting the next
> group.
>
> Let's say I've got 26 vservers, 'A'-'Z' and I want them to start in the
> order 'Z'-'A'. So I make 'Y' depend on 'Z', 'X' depend on 'Y', etc.
> But in that case, they start one at a time each one waiting until the
> next is started. Starting 26 vservers one at a time takes WAY too long.
>
> Now imagine that I've told it to start 6 at a time. So I make 'O'-'P'
> depend on 'U'-'Z', 'I'-'N' depend on 'O'-'P', etc. But now the WHOLE
> group of 6 needs to start before the next group will start. So I'm at
> the mercy of the slowest starting vserver in each group.
>
> So I make 'O'-'P' depend only on 'U', or 'Z', or whichever one I want.
> But the scripts still wait until that vserver starts before it starts
> any more. So there is still waiting time unless I always specify the
> fastest vserver as the dependency.
>
> But even in that case, each group of 6 still starts alphabetically
> within the group. 'O' then 'P' then 'Q', etc. There's no way to make
> 'S' first in this group of 6 unless I set that 'O' and 'P' and 'Q' and
> 'R' depend on 'S', which means I'm back to waiting while a single
> vserver starts before the others start.
>
> And if I want to start more or less at a time, I have to redo all the
> depends files, because I set them up assuming 6 to start at the same time.
>
> With the 'startorder' file, the vservers are started in the order I
> specify and there's no waiting. If I'm starting 6 at a time, then
> numbers 1-6 start and as soon as any of them finished (doesn't matter
> which one), number 7 starts, then 8, etc. There's always 6 vservers
> starting and they start in the order I specify.
>
> If I change to starting 8 a time, then 1-8 start and 9 starts as soon as
> any of those 8 finish, and so on.
>
> If I've totally missed how to use the 'depends' file, then I'd love to
> hear how I can use it to accomplish my goals - start/stop my vservers in
> a particular order and always keep X number starting/stopping at the
> same time. But this patch does that for us. And the only affect it has
> if you don't use the 'startorder' files is that vservers stop in reverse
> alphabetical order (assuming no 'depends' files). That could be easily
> changed if it's a problem.

I still fail to see why you care what order they start in. If you don't
have explicit dependencies between them, i.e. you don't use depends, then
why does it matter? If you just set the number of parallel starts to
whatever number you want, that is the number that will be running at once,
all the time.

-- 
Daniel Hokka Zakrisson