Re: What is a savepointLevel ?

On Fri, 15 Mar 2019 at 18:18, Chapman Flack <chap(at)anastigmatix(dot)net> wrote:
> What exactly is a savepointLevel?
>
> They seem to have been there for 15 years[1], diligently copied from
> parent transactions to children, fastidiously checked to avoid crossing
> a level on rollback or release, but does anything ever change the level
> from its initial value? I'm drawing a blank[2].

I had a look too, checking for uses where savepointLevel might be set
as part of a struct initialisation. I can't find any.

There's some discussion about it in July 2004.

https://www.postgresql.org/message-id/flat/Pine.LNX.4.58.0407101609080.4563%40linuxworld.com.au#dad1807aaa73de2be7070a1bc54d0f6b

https://www.postgresql.org/message-id/flat/5902.1090695230%40sss.pgh.pa.us#53d8db46b7f452acd19ec89fcb023e71

Adding the field was committed on the 27th.

(I'm very ignorant on the following.)

It looks like the point of savepoint levels is to distinguish between
savepoints created in the top transaction level versus those created
in nested function calls, and to stop you from trying to
release/rollback to a savepoint belonging to the outer scope. But I
don't think we support savepoints from inside functions of any kind.
Various PLs use BeginInternalSubTransaction and they handle the
rolling back/releasing internally.

So the savepointLevel variable, and the two error checks that use it,
look a bit unused. If SAVEPOINT commands were supported in functions,
you'd want to increment savepointLevel when you made a subtransaction
on entering the function.

Does that sound approximately right?

Edmund

> [1]
> https://git.postgresql.org/gitweb/?p=postgresql.git;a=blame;f=src/backend/access/transam/xact.c;h=fd5d6b5;hb=90cb9c3#l93
>
> [2]
> https://git.postgresql.org/gitweb/?p=postgresql.git&a=search&h=0516c61b&st=grep&s=savepointLevel