* Andres Freund (and...@anarazel.de) wrote: > On Monday, December 19, 2011 03:33:22 PM Alvaro Herrera wrote: > > > I do like the idea of putting the CRC info in a relation fork, if it can > > > be made to work decently, as we might be able to then support it on a > > > per-relation basis, and maybe even avoid the on-disk format change.. > > > > > I think the main objection to that idea was that if you lose a single > > page of CRCs you have hundreds of data pages which no longer have good > > CRCs. > Which I find a pretty non-argument because there is lots of SPOF data in a > cluster (WAL, control record) anyway... > If recent data starts to fail you have to restore from backup anyway.
I agree with Andres on this one.. Also, if we use CRC on the pages in
the CRC, hopefully we'd be able to detect when a bad block impacted the
CRC fork and differentiate that from a whole slew of bad blocks in the
heap..
There might be an issue there with handling locking and having to go
through the page-level lock on the CRC, which locks a lot more pages in
the heap and therefore reduces scalability.. Don't we have a similar
issue with the visibility map though?
Thanks,
Stephen
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