Re: Why does PostgreSQL ftruncate before unlink?

On Sunday, February 23, 2014, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:

> On Fri, Feb 21, 2014 at 4:14 PM, Jon Nelson <jnelson+pgsql(at)jamponi(dot)net<javascript:;>>
> wrote:
> > When dropping lots of tables, I noticed postgresql taking longer than
> > I would have expected.
> >
> > strace seems to report that the largest contributor is the ftruncate
> > and not the unlink. I'm curious what the logic is behind using
> > ftruncate before unlink.
> >
> > I'm using an ext4 filesystem.
>
> I'm guessing that this is so that it can be rolled back. Unlink is
> likely issued at commit;
>

I would hope that ftruncate is issued at commit as well. That doesn't
sound undoable.

Cheers,

Jeff