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From: Phil Frost <phil@macprofessionals.com>
Subject: Re: error in documentation?
Date: Mon, 24 Sep 2007 10:15:57 -0400
To: Michael Cochez <michaelcochez@yahoo.com>


On Sep 24, 2007, at 10:03 , Michael Cochez wrote:

> In http://www.postgresql.org/docs/8.2/static/tutorial- 
> transactions.html
> "After rolling back to a savepoint, it continues to be defined, so  
> you can roll back to it several times. Conversely, if you are sure  
> you won't need to roll back to a particular savepoint again, it can  
> be released, so the system can free some resources. Keep in mind  
> that either releasing or rolling back to a savepoint will  
> automatically release all savepoints that were defined after it."
> mustn't it be :
> "After rolling back to a savepoint, it continues to be defined, so  
> you can roll back to it several times. Conversely, if you are sure  
> you won't need to roll back to a particular savepoint again, it can  
> be released, so the system can free some resources. Keep in mind  
> that rolling back to a savepoint will automatically release all  
> savepoints that were defined after it and releasing a savepoint  
> will automatically release all savepoints defined before it."
>
> if not, could you please explain why this decision is made?
> thanks,
> Michael


If I do:

savepoint one;
update foo set bar = 2;
savepoint two;
update baz set foo = 3;
savepoint three;
delete from foo;

Why would it make sense to release "one" if i release "two"? If I  
release "two", then it makes sense that I can never go back to "two"  
or "three", but your proposed change means that if I release "two", I  
can later rollback to "three" but not to "one". I don't see how  
that's useful.

Essentially what the docs say is that savepoints are created on a  
stack, and when you do something to to a savepoint "s", you  
implicitly do the same thing to all the other savepoints above "s".  
Or, if you think of them being nested:

savepoint one {
   update foo set bar = 2;
   savepoint two {
     update baz set foo = 3;
     savepoint three {
       delete from foo;
       ...
     }
     ...
   }
   ...
}

then any operation on a savepoint also applies to any savepoints  
nested within it.