On 12/11/12 05:55, Greg Smith wrote:
> The only guarantee I see that we can give for online upgrades is that
> after a VACUUM CHECKSUM sweep is done, and every page is known to both
> have a valid checksum on it and have its checksum bits set, *then* any
> page that doesn't have both set bits and a matching checksum is
> garbage. Until reaching that point, any old data is suspect. The
> idea of operating in an "we'll convert on write but never convert old
> pages" can't come up with any useful guarantees about data integrity
> that I can see. As you say, you don't ever gain the ability to tell
> pages that were checksummed but have since been corrupted from ones
> that were corrupt all along in that path.
You're right about that, but I'd just like some rough guard against
hardware/OS related data corruption.
and that is more likely to hit data-blocks constantly flying in and out
of the system.
I'm currently running a +2TB database and the capabillity to just see
some kind of corruption earlier
rather than later is a major benefit by itself. Currently corruption can
go undetected if it just
happens to hit data-only parts of the database.
But I totally agree that the scheme described with integrating it into a
autovacuum process would
be very close to ideal, even on a database as the one I'l running.
--
Jesper
