Re: Problems with postgres online backup - restore

Gerhard Wiesinger wrote:
> Hello,
> 
> I'd like to understand the PostgreSQL internals in "backup mode".
> 
> When I understood it correctly pg_start_backup() make a checkpoint and 
> stops writing to the data/ directory except the WAL.
> 
> All new transaction go into WAL which is also logical. But how is data 
> consistency done when the written/changed blocks don't fit into the 
> buffer cache?

The data isn't kept consistent. Which is why you need the WAL. Restoring 
from a PITR backup is basically the same idea as recovering from a 
crash. Any blocks that might have been updated since you called 
pg_start_backup() will be rewritten from the WAL.

-- 
   Richard Huxton
   Archonet Ltd