Re: In-placre persistance change of a relation

I want to call out this part of this patch:

> Also this allows for the cleanup of files left behind in the crash of
> the transaction that created it.

This is interesting to a lot wider audience than ALTER TABLE SET 
LOGGED/UNLOGGED. It also adds most of the complexity, with the new 
marker files. Can you please split the first patch into two:

1. Cleanup of newly created relations on crash

2. ALTER TABLE SET LOGGED/UNLOGGED changes

Then we can review the first part independently.

Regarding the first part, I'm not sure the marker files are the best 
approach to implement it. You need to create an extra file for every 
relation, just to delete it at commit. It feels a bit silly, but maybe 
it's OK in practice. The undo log patch set solved this problem with the 
undo log, but it looks like that patch set isn't going anywhere. Maybe 
invent a very lightweight version of the undo log for this?

- Heikki