On 11/12/2012 10:44 AM, Craig Ringer wrote:
> That'll make it hard for VACUUM, hint-bit setting, etc to
> opportunistically checksum pages whenever they're doing a page write anyway.
It *is* a hard problem, yes. And the single bit doesn't really solve it.
So I'm arguing against opportunistically checksumming in general. Who
needs that anyway?
> Is it absurd to suggest using another bitmap, like the FSM or visibility
> map, to store information on page checksumming while checksumming is
> enabled but incomplete?
Not absurd. But arguably inefficient, because that bitmap may well
become a bottleneck itself. Plus there's the problem of making sure
those pages are safe against corruptions, so you'd need to checksum the
checksum bitmap... doesn't sound like a nice solution to me.
This has certainly been discussed before.
Regards
Markus Wanner