Re: Differential backup

On 04/27/2010 09:59 AM, Kevin Grittner wrote:
> Under what circumstances would PostgreSQL
> modify a file without changing the "last modified" timestamp or the
> file size?

Do all OSes have sub-second precision mtimes? Because otherwise I could 
see a scenario such at this:

* File is modified
* Backup inspects and copies the file in the same second
* File is modified again in the same second, so the mtime doesn't change
* Backup is run again some time later and sees that the mtime has not 
changed

Even with microsecond precision this kind of scenario makes me squidgy, 
especially if some OSes decide that skipping frequent mtime updates is 
OK. Florian's point about clock changes is also very relevant. Since 
Postgres has the capability to give a better answer about what is in the 
file, it would be best to use that.

-- m. tharp