Re: Page-at-a-time Locking Considerations

On Mon, 2008-02-04 at 20:54 +0000, Simon Riggs wrote:
> On Mon, 2008-02-04 at 20:03 +0000, Gregory Stark wrote:
>
> > I wonder how hard it would be to shove the clog into regular shared
> > memory pages and let the clock sweep take care of adjusting the
> > percentage of shared mem allocated to the clog versus data pages.
>
> There is a reason that's not been done... try it and see.
>
> Plus it doesn't fully resolve the main issue as described.

On further thought, there may be a way to do as Greg suggests.

We keep clog pages in shared buffers, but maintain a vestigial slru
structure that provides fast lookup to the N most recently accessed
pages. So we don't keep a physical slru buffer space anymore, we just
keep pointers to shared buffers. Slru "I/O" then becomes a swapping of
entries on the slru fast lookup structure, but hopefully not I/O out of
shared_buffers.

When we move out of clog buffers we *may* need to write the page
immediately because of async LSNs, but that seems OK.

That solution sounds weird at first, but seems much less yuck than
mmap() style solutions.

--
Simon Riggs
2ndQuadrant http://www.2ndQuadrant.com