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SubjectRE: Killing/balancing processes when overcommited
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On Fri, 2002-09-13 at 15:31, Timothy D. Witham wrote:
>
> On Fri, 2002-09-13 at 14:13, Jim Sibley wrote:
> >
> >
> > Tim wrote:
> > > There is another solution. And that is never >allocate memory unless
> > >you have swap space. Yes, the issue is that you >need to have lots of
> > >disk allocated to swap but on a big machine you >will have that space.
> >
> > How do you predict if a program is going to ask for more memory? Maybe it only
> > needs additional memory for a short time and is a good citizen and gives it
> > back?
> >
>
> Well its been a bit so the details are fuzzy but you have a pointer

Counter, I meant to say "a counter as to " instead of "a pointer to".

:-)

> to how much space you have left in you allocated swap and when you get
> memory you decrement space and when you release memory in increment it
> so that it indicates how much you have left. If you try and malloc
> more than you free then you go and reserve another chunk of swap.
>
> > How much disk needs to be allocated for swap? In 32 bit, each logged in user
> > is limited to 2 GB, so do we need 2 GB for each logged on user? 250 users, 500
> > GB of disk?
> >
>
> It turns out that for the high load database machines this is about
> 3 to 4 times the actual physical memory.
>
>
> > In a 64 bit system, how much swap would you reserve?
> >
>
> Same as 32 bit machines doesn't apply.
>
>
> > Actually, another OS took this approach in the early 70's and this was quickly
> > junked when they found out how much disk they really had to keep in reserve
> > for paging.
> >
>
> But there are many current OS's that do this and are quite successful.
>
> > > This way the offending process that asks for >more memory will be
> > >the one that gets killed. Even if the 1st couple >of ones aren't the
> > >misbehaving process eventually it will ask for >more memory and suffer
> > >process execution.
> >
> > It may not be the "offending process" that is asking for more memory. How do
> > you judge "offending?"
> >
>
> In this case the offense is asking for more memory. So it is the
> process that asks for more memory that goes away. Again sometimes
> it will be an innocent bystander but hopefully it will eventually
> be the process that is causing the problem.
>
> Many databases program for this condition. The stuff that absolutely
> must be up and running preallocates all of the memory that it needs
> at startup. Any new memory requests that are denied might cause a
> transaction to fail but they won't bring down the whole database.
>
> Tim
> >
> >
> >
> >
> --
> Timothy D. Witham - Lab Director - wookie@osdlab.org
> Open Source Development Lab Inc - A non-profit corporation
> 15275 SW Koll Parkway - Suite H - Beaverton OR, 97006
> (503)-626-2455 x11 (office) (503)-702-2871 (cell)
> (503)-626-2436 (fax)
>
> -
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--
Timothy D. Witham - Lab Director - wookie@osdlab.org
Open Source Development Lab Inc - A non-profit corporation
15275 SW Koll Parkway - Suite H - Beaverton OR, 97006
(503)-626-2455 x11 (office) (503)-702-2871 (cell)
(503)-626-2436 (fax)

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