Re: Add checksums without --initdb

On 07/02/2015 11:28 PM, Andres Freund wrote:
> On 2015-07-02 22:53:40 +0300, Heikki Linnakangas wrote:
>> Add a "enabling-checksums" mode to the server where it calculates checksums
>> for anything it writes, but doesn't check or complain about incorrect
>> checksums on reads. Put the server into that mode, and then have a
>> background process that reads through all data in the cluster, calculates
>> the checksum for every page, and writes all the data back. Once that's
>> completed, checksums can be fully enabled.
>
> You'd need, afaics, a bgworker that connects to every database to read
> pg_class, to figure out what type of page a relfilenode has. And this
> probably should call back into the relevant AM or such.

Nah, we already assume that every relation data file follows the
standard page format, at least enough to have the checksum field at the
right location. See FlushBuffer() - it just unconditionally calculates
the checksum before writing out the page. (I'm not totally happy about
that, but that ship has sailed)
- Heikki