Re: Block-level CRC checks

On Sun, Nov 09, 2008 at 11:02:32AM -0500, Tom Lane wrote:
> Yes it would :-(.  Also, this scheme would point us towards maintaining
> the CRCs *continually* while the page is in memory, rather than only
> recalculating them upon write.  So every tuple insert/update/delete
> would require a recalculation of the entire page CRC.

I wasn't thinking of that. I was thinking more of the situation where a
seq scan reads in a page, updates a few hint bits and then goes on to
the next page. For these just doing a few XORs might be cheaper.

> What happened to the plan to double-buffer the writes to avoid this
> issue?

Might be better anyway. A single copy-and-checksum would probably be
quite cheap (pulling the page into L2 cache).

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Please line up in a tree and maintain the heap invariant while
> boarding. Thank you for flying nlogn airlines.