[mythtv-users] 0.25 SQL CPU Load issues after optimisation

Michael T. Dean mtdean at thirdcontact.com
Mon Jul 23 14:02:47 UTC 2012

On 07/21/2012 06:24 AM, Mike Perkins wrote:
> On 20/07/12 22:54, Another Sillyname wrote:
>> I cleaned up the rules and while doing so came across something that
>> could be a conflict.
>> When I originally built the system as a combined Freeview and Freesat
>> service the CHANID values get set according to the order that the
>> source device is chosen.
>> In my original build I'd actually scanned the DVB-T channels twice
>> from two different DVB-T tuners as I didn't realise that the source
>> could be shared by the other tuners.  So then when I scanned the DVB-S
>> channels there was a 4000 offset for the SID and therefore CHANID, for
>> example BBC HD which has a SID of 6940 got allocated a CHANID of 10940
>> to allow for the offset.
>> When I did the recent rebuild I didn't make the same error so the SID
>> and CHANID were instead 8940 rather then the original 10940.  This
>> means the database had recording rules for CHANID values that just
>> didn't exist in the database anymore.
>> I've cleaned the rules down from 750+ to about 150 and will monitor
>> for a few more days, if I'm right it'll be worth putting this into the
>> wiki so it doesn't catch out other users later.
>> Fingers crossed but good job guys.
> That raises an important question that wouldn't have bothered us in 
> the old analog days.
> In the digital world, channels are getting moved about on a fairly 
> frequent basis which means we end up rescanning more than we used to. 
> End result: CHANID for any particular channel can get changed from 
> time to time.
> This means that "record on channel xxx" rules are likely not going to 
> work after a scan. I have some of these, and they are a pain to try 
> and figure out which channel they referred to, as they display as 
> "Record on channel ." - that is, the history is gone.

Yes, this is why "this channel" rules are generally discouraged--because 
they require you to re-create the rules after any changes to your channels.

> Is there any chance that in the future these rules won't be tied to 
> CHANID but some other identifier like CALLSIGN, perhaps? (Remembering 
> for those of you in the US that CALLSIGN can be a /lot/ longer than 
> 5-6 characters elsewhere in the world.) Not necessarily CALLSIGN 
> itself, perhaps, but a uniqueid indexed on CALLSIGN.

FWIW, they are tied to callsign--the callsign of the channel referenced 
by the given ID.  Note, also, that on rescanning it's /quite/ common for 
callsign to change, too--so changing the code/DB to reference callsign 
or station would only trade one problem for another, and you'd almost 
definitely have to keep re-creating any "this channel" rules.

"Any channel" rules work before and after rescans, regardless of what 


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