Checkpoint validity

On Sep 11,  6:28, Roger Hill wrote:
> Subject: Re: Re[2]: Journaling Question...really dumb!
> .....
> The only thing that now nags at me is under what circumstances a
> checkpoint is useless...

An interesting question.

A checkpoint is useless if:

1. It's an online checkpoint and you don't have the contents of the dmp
directory AS OF CHECKPOINT COMPLETION.

2. Any of the locations (eg data locations) referenced by the database
change paths, or disappear.

I think #1 is the only condition that will make a checkpoint unrecoverably
useless.  #2 is technically fixable, but liable to be hard to fix if you
run into it.  (Am I missing anything major, guys?)
There are of course other situations that will make a checkpoint useless,
but are recoverable IF you are careful.

Careful means that you have a safe copy of the checkpoint AND the dmp stuff
somewhere, such that you can restore either/both if you screw up.

I suppose the most common recoverable situation is that the database
is gone (destroyed).  You recover by creating the database, being careful
to use the same data location(s); play some games with the aaaaaaaa.cnf
file; and rollforward will work.  This trick and similar ones are all
covered in suitable detail by the various papers by Mike Leo and others.

I confess to not having much experience in dealing with problems rolling
journals forward, or dealing with offline checkpoints.  Journal rollforward
seems to be one of those things that works or doesn't.
I also have no experience with the OpenIngres partial (table) checkpoints.

-- 
Karl Schendel            Phone: (412) 963-8844
Telesis Computer Corp      Fax: (412) 963-1373
wiz@telesis.com



Hi Roger,
 
 One thing I've come across recently.  If you disaster recovery plan 
 involves putting your databases on a replacement box and rollforwarddb 
 the checkpoints, you need to have a copy of the aaaaaaaa.cnf file from 
 the data or dmp location taken AFTER successful completion of the 
 checkpoint.  The content of this version marks the ckp you just did as 
 valid - allowing a rollforwarddb operation.
 It also helps if you have a script or an archive to re-create the 
 directory structure down to .../data/default/ and to reset 
 the UNIX permissions - it saves doing by hand and getting it wrong (it 
 gave me a real wobbler when my rollforwarddb didn't work first time!)
 
 Hope this helps,    Colin.
 
 +------------------------------------+-------------------------+
 | Colin MacKellar                    |  Database Manager       |
 +------------------------------------+  Perot Systems Europe   |
 | Tel  +44 (0)115 966 2177           |  398 Coppice Road       |
 | Fax  +44 (0)115 966 2091           |  Arnold                 |
 | E-mail Colin.MacKellar@ps.net      |  Nottingham     NG5 7HX |
 +------------------------------------+-------------------------+
Ingres Q & A
To William's Home Page
Email William