On Tue, Mar 6, 2012 at 5:50 PM, Bruce Momjian <bruce@momjian.us> wrote:
> One crazy idea would be to have a checksum _version_ number somewhere on
> the page and in pg_controldata. When you turn on checksums, you
> increment that value, and all new checksum pages get that checksum
> version; if you turn off checksums, we just don't check them anymore,
> but they might get incorrect due to a hint bit write and a crash. When
> you turn on checksums again, you increment the checksum version again,
> and only check pages having the _new_ checksum version.
>
> Yes, this does add additional storage requirements for the checksum, but
> I don't see another clean option. If you can spare one byte, that gives
> you 255 times to turn on checksums; after that, you have to
> dump/reload to use the checksum feature.
I like the idea very much actually. But I'll let you argue the case
for using pd_pagesize_version for that with your esteemed colleagues.
It would be pretty safe to just let it wrap.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
