[mythtv-users] Using same database with trunk and release

Michael T. Dean mtdean at thirdcontact.com
Sun May 6 04:32:47 UTC 2007


On 05/05/2007 06:52 AM, Brian L. Walter wrote:
> Chad wrote:
>   
>> On 5/4/07, John Overchuk <overchuk at hotmail.com> wrote:
>>     
>>> If I have a database that was created and used with the latest trunk builds,
>>> any thoughts on how well it would work if I tried to use the release version
>>> of myth with it?
>> Depends.  I "accidently" did that a while back while testing out the
>> -vid branch (without realizing it was going to change my db) and
>> haven't had many issues since, and shortly after I tested the -vid
>> branch I reverted back to .20-fixes and have been running it for quite
>> some time.  I do have a few hiccups occasionally and I do blame my
>> lack of backup-prior-to-db-change for the hiccups, but it wasn't like
>> I had to wipe the slate clean and start over.
>>
>> The other side of the that depends is that it was quite a while ago
>> and .20-fixes and -vid weren't that different of db schemas (it was
>> shortly after the .20 release) while today an SVN schema and a
>> .20-fixes schema may be entirely incompatible.
> I've had pretty much the same experience.  It looks like, from the code, 
> that selects etc are done via direct column names.  If thats true, I 
> doubt that colums got *dropped* in updates, so the net would be that you 
> have more information in the database than you are actually using.
>
> And it doesn't appear that Myth uses things like stored procedures or 
> triggers (I didn't see any stored procedures defined in the schema...not 
> sure about triggers), so, it might work, and as mentioned above, you 
> might have a few hiccups.
>
> I've gone from 0.21 back to 0.20 rpm to 0.20-svn back to 0.20 rpm (which 
> is now 0.20.1), and the only things that I have issues with are 
> ff/rewind and closed captions.  However, FF/rewind broke when I went to 
> trunk, so not sure if it's related.

Note, though, that however well it may seem to work, doing so is 
completely unsupported.  If you have issues and ask questions on the 
list, you should mention, "I'm running 0.20-fixes SVN with trunk DB 
schema version XXXX," so people like me will know to ignore the question 
rather than waste a bunch of time trying to figure out why your system 
is working right--when the actual answer is, "Because you're using the 
wrong DB."

And, BTW, trunk's DB schema is currently very different from 0.20-fixes

And in truth, the DB updates don't just change the schema--they often 
fix old data formats to be compatible with the schema updates.  That 
means that if you upgrade to SVN trunk today, your old data gets 
upgraded to the new format.  Then if you downgrade to 0.20-fixes, you 
will start inserting more /old-format/ data into the DB.  Then, when 
0.21 comes out, you'll upgrade and all that "new" old-format data (i.e. 
that inserted since the downgrade) will /not/ be converted (because your 
database is already new format--even though you've been inserting 
old-format data into it).  So basically, you're running an unsupported 
configuration today, then tomorrow you pay a big price for it when your 
old data gets broken.  It's a DB time bomb.

I /highly/ recommend you never do a downgrade unless you do so by 
restoring a pre-upgrade backup.

Mike


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