Re: Block-level CRC checks

So this discussion died with no solution arising to the
hint-bit-setting-invalidates-the-CRC problem.

Apparently the only solution in sight is to WAL-log hint bits.  Simon
opines it would be horrible from a performance standpoint to WAL-log
every hint bit set, and I think we all agree with that.  So we need to
find an alternative mechanism to WAL log hint bits.

I thought about causing a process that's about to write a page check a
flag that says "this page has been dirtied by someone who didn't bother
to generate WAL".  If the flag is set, then the writer process is forced
to write a WAL record containing all hint bits in the page, and only
then it is allowed to write the page (and thus calculate the new CRC).

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.