> > How do you get atomic block copies otherwise?
> 
> Eh?  The kernel does that for you, as long as you're reading the
> same-size blocks that the backends are writing, no?

Good point.

Vadim

Fri, 2 Aug 2002 15:01:11 -0700 
"Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
Re: PITR, checkpoint, and local relations 
Are you sure this is true for all ports? And if so, why would it be
cheaper for the kernel to do it in its buffer manager, compared to us
doing it in ours? This just seems bogus to rely on. Does anyone know
what POSIX has to say about this? 

On Fri, 2002-08-02 at 18:01, Mikheev, Vadim wrote:
> > > How do you get atomic block copies otherwise?
> > 
> > Eh?  The kernel does that for you, as long as you're reading the
> > same-size blocks that the backends are writing, no?
> 
> Good point.
> 
> Vadim
> 
-- 
J. R. Nield
jrnield@usol.com




02 Aug 2002 18:24:07 -0400
"J. R. Nield" <jrnield@usol.com>
Re: PITR, checkpoint, and local relations


> -----Original Message-----
> From: Mikheev, Vadim [mailto:vmikheev@SECTORBASE.COM]
> Sent: Friday, August 02, 2002 6:01 PM
> To: 'Tom Lane'; J. R. Nield
> Cc: Richard Tucker; Bruce Momjian; PostgreSQL Hacker
> Subject: RE: [HACKERS] PITR, checkpoint, and local relations
>
>
> > > How do you get atomic block copies otherwise?
> >
> > Eh?  The kernel does that for you, as long as you're reading the
> > same-size blocks that the backends are writing, no?
>
> Good point.
>
We know for sure the kernel does this?  I think this is a dubious
assumption.
> Vadim
>


Wed, 07 Aug 2002 11:32:01 -0400
Richard Tucker <richt@multera.com>
Re: PITR, checkpoint, and local relations
Richard Tucker <richt@multera.com> writes:
>>> Eh?  The kernel does that for you, as long as you're reading the
>>> same-size blocks that the backends are writing, no?

> We know for sure the kernel does this?  I think this is a dubious
> assumption.

Yeah, as someone pointed out later, it doesn't work if the kernel's
internal buffer size is smaller than our BLCKSZ.  So we do still need
the page images in WAL --- that protection against non-atomic writes
at the hardware level should serve for this problem too.

			regards, tom lane

Wed, 07 Aug 2002 11:40:34 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: PITR, checkpoint, and local relations 