On Jan 22, 2017 11:13 AM, "Magnus Hagander" <mag...@hagander.net> wrote:

Yes, this means the entire db will end up in the transaction log since
everything is rewritten. That's not great, but for a lot of people that
will be a trade they're willing to make since it's a one-time thing. Yes,
this background process might take days or weeks - that's OK as long as it
happens online.

I'm not sure that's actually necessary. You could just log a wal record
saying "checksum this block" and if it gets replayed then recalculate the
checksum on that block again. This record could be exempt from the usual
rules for having a fpw.

There's no danger of torn pages from the checksum alone. The danger would
be if some other operation does dirty that page then your need to know that
the page is in this weird in between state where it's dirty but not yet had
a fpw written.

I'm not sure whether it's worth the infrastructure to have such a state
just for this or not. On the other hand it sounds like something that would
be useful.

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