[mythtv-users] Howto prevent MythTV flushing/Syncing disk writes (LiveTV/Recordings)

[Brian Foddy]

On Tuesday 18 March 2008, David Rees wrote:
> On Tue, Mar 18, 2008 at 6:09 AM, Albert Graham <agraham at g-b.net> wrote:
> > Does anyone know how to prevent MythTV from flushing/syncing every
> > single write request when watching LiveTV or  recording something.
> >
> > My machine has lots of memory and very large fast disks, so I would
> > prefer writes to occur in much larger chunks and a lot less often,
> > rather than every 3 or so MB.
>
> Yes, as David Brodbeck mentioned, MythTV explicitly syncs video data to
> disk every 250ms or so because "back in the day" some systems did
> encounter hiccups when letting the OS flush data out to disk as it saw
> fit. In some cases the amount of time it took to flush data to disk
> took to long so this would cause playback to hiccup as the disk was
> too busy writing (and not enough video was buffered to make up for it)
> or recordings to hiccup as the disk writing process interrupted the
> read process.
>
> I also would prefer to let the data get flushed out automatically as
> this would reduce the constant clatter of the disks. Or at least make
> the sync interval configurable.
>
> If you want to fix this, you're going to have to dig into the source code.
>
> -Dave
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I'm a little late to this party, catching up on threads, but for several
years I've "usually" just commented out the whole 
ThreadedFileWriter::Sync method and just let the OS flush when
it wants to.  But I have between 5 and 7 recording (3 HD and 4 SD) tuners
running at a time and I figure the artificial flushing is probably negative.
TBH, I don't see much difference with good performing disks.

Brian