Re: Page Checksums + Double Writes

Excerpts from David Fetter's message of mié dic 21 18:59:13 -0300 2011:

> 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.

If you get away with a new page format, let's make sure and coordinate
so that we can add more info into the header.  One thing I wanted was to
have an ID struct on each file, so that you know what
DB/relation/segment the file corresponds to.  So the first page's
special space would be a bit larger than the others.

--
Álvaro Herrera <alvherre@commandprompt.com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support