Re: Enabling Checksums

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