On 04/23/2015 06:38 PM, Bruce Momjian wrote:
On Thu, Apr 23, 2015 at 10:42:59AM +0300, Heikki Linnakangas wrote:
On 04/22/2015 09:24 PM, Robert Haas wrote:
I would feel safer if we added a completely new "epoch" counter to the page
header, instead of reusing LSNs. But as we all know, changing the page
format is a problem for in-place upgrade, and takes some space too.
Yeah. We have a serious need to reduce the size of our on-disk
format. On a TPC-C-like workload Jan Wieck recently tested, our data
set was 34% larger than another database at the beginning of the test,
and 80% larger by the end of the test. And we did twice the disk
writes. See "The Elephants in the Room.pdf" at
https://sites.google.com/site/robertmhaas/presentations
Meh. Adding an 8-byte header to every 8k block would add 0.1% to the
disk size. No doubt it would be nice to reduce our disk footprint,
but the page header is not the elephant in the room.
Agreed. Are you saying we can't find a way to fit an 8-byte value into
the existing page in a backward-compatible way?
I'm sure we can find a way. We've discussed ways to handle page format
updates in pg_upgrade before, and I don't want to get into that
discussion here, but it's not trivial.
- Heikki
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