Re: emergency outage requiring database restart

Jim Nasby wrote:
> On 10/21/16 2:02 PM, Alvaro Herrera wrote:
> > Merlin Moncure wrote:
> > 
> > > OK, I have some good (very- in the specific case of yours truly) news
> > > to report.  Doing a filesystem level copy to a test server I was able
> > > to relfilenode swap one of the critical tables over the place of the
> > > refilenode of the stored backup.  Not being able know the file to copy
> > > from, I figured out the source node by judging the size and using
> > > 'strings'  utility.  Data recovery for that table at least appears to
> > > be 100%.
> > 
> > FWIW you can use pg_filedump and match based on the number of columns.
> > I suppose you could also use the pageinspect extension, by 'dd'ing a
> > page from the file into the database and feeding into heap_page_items as
> > bytea.
> 
> It occurs to me that it might be worth embedding the relation name in the
> free space of the first block. Most people would never notice the missing 64
> bytes, but it would be incredibly helpful in cases like this...

Agreed.  The problem is how to install it without breaking pg_upgrade.

Note that for DR purposes it is better to put that data in the first
block of *each segment*.  Otherwise if you have many >1GB tables, you
have to go segment by segment ...

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services