Folks, One of the things VMware is working on is double writes, per previous discussions of how, for example, InnoDB does things. I'd initially thought that introducing just one of the features in $Subject at a time would help, but I'm starting to see a mutual dependency.
The issue is that double writes needs a checksum to work by itself, and page checksums more broadly work better when there are double writes, obviating the need to have full_page_writes on. If submitting these things together seems like a better idea than having them arrive separately, I'll work with my team here to make that happen soonest. There's a separate issue we'd like to get clear on, which is whether it would be OK to make a new PG_PAGE_LAYOUT_VERSION. If so, there's less to do, but pg_upgrade as it currently stands is broken. If not, we'll have to do some extra work on the patch as described below. Thanks to Kevin Grittner for coming up with this :) - Use a header bit to say whether we've got a checksum on the page. We're using 3/16 of the available bits as described in src/include/storage/bufpage.h. - When that bit is set, place the checksum somewhere convenient on the page. One way to do this would be to have an optional field at the end of the special space based on the new bit. Rows from pg_upgrade would have the bit clear, and would have the shorter special structure without the checksum. Cheers, David. -- David Fetter <da...@fetter.org> http://fetter.org/ Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter Skype: davidfetter XMPP: david.fet...@gmail.com iCal: webcal://www.tripit.com/feed/ical/people/david74/tripit.ics Remember to vote! Consider donating to Postgres: http://www.postgresql.org/about/donate -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
