Re: Online enabling of checksums

Hi,

While looking at the online checksum verification patch (which I guess
will get committed before this one), it occurred to me that disabling
checksums may need to be more elaborate, to protect against someone
using the stale flag value (instead of simply switching to "off"
assuming that's fine).

The signals etc. seem good enough for our internal stuff, but what if
someone uses the flag in a different way? E.g. the online checksum
verification runs as an independent process (i.e. not a backend) and
reads the control file to find out if the checksums are enabled or not.
So if we just switch from "on" to "off" that will break.

Of course, we may also say "Don't disable checksums while online
verification is running!" but that's not ideal.


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services