[mythtv-users] how to make 0.24 more like 0.21 ?

[Roger Horner]

On Wed, Oct 26, 2011 at 3:14 PM, Jay Ashworth <jra at baylink.com> wrote:

> ----- Original Message -----
> > From: "Roger Horner" <mythtvuser1818 at gmail.com>
>
> > > On Wed, Oct 26, 2011 at 10:17 AM, Tyler T <tylernt at gmail.com> wrote:
>
> > > So far it looks like turning off swap (the machine has 1G of RAM and
> > > Mythbuntu set up an additional 1G of swap) fixed it.
> > > Kinda strange, since before it was using something like 700M RAM
> > > plus 800M swap, and now it's just using 900M RAM.
> > >
> > Interesting! On my previous system (which only had 512MB RAM) I often
> > guessed that the stuttering was caused by it swapping out to disk, but
> > I always thought that problem was I didn't have enough RAM (which may
> > also have been true in my case). In my current system (which has 2GB
> RAM),
> > I have noticed that if it has been on for a while, almost all the RAM
> > will be used and a small amount of swap is also used, which has always
> seemed
> > strange to me.
> >
> > I seem to remember reading that MythTV will fill up all unused RAM
> > with a buffer of recently recorded video to save on disk reads if another
> > process needs it. I wonder if there is a bug where when there is need for
> more
> > RAM it gets it from swap before freeing up space from this buffer? I
> think
> > I will turn off my swap space and see what happens (I only added it
> > because it seemed like a good idea at the time).
>
> You might want to reconsider.
>
> Unlike Windows, on which the rule is "swap early and often", and where that
> particular tradeoff might be worthwhile, on Linux, processes are not paged
> out until there's no memory left, in general.
>
> The reason the free space indication goes down is that Linux tends to
> allocate
> most unused space for its buffer cache, adjusting as necessary when the ram
> is needed for programs.
>

Isn't that what I said (though I incorrectly thought it was Myth not
Linux)?  My question is why would it use swap space if there is a buffer
cache?


> 512MB really *isn't* enough ram, but if that's all you have, you'd better
> leave
> swap enabled, or you'll run out of memory and things will start getting
> killed.
>

I agree, but that was my old system.  My new one has 2GB, which should be
enough for a combined Front and Backend (nothing else), but it still seems
to start using a bit of swap space if the system has been on for a while.


> If you haven't already done it, making sure your OS and SQL are on one
> physical drive, and your video on another, is probably the easiest solution
> to disk contention problems.
>

Already done.  Small boot drive has OS and SQL (plus some space for
MythVideo data).  Large secondary drive has all my recordings.  I haven't
really been having any "disk problems" per say with the new systems, just
curiuous that it would need to use swap at all.
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