Re: FPW compression leaks information

On Wed, Apr 15, 2015 at 11:55 AM, Michael Paquier wrote:
> OK. I am fine to implement anything required here if needed, meaning
> the following:
> 1) Doc patch to mention that it is possible that compression can give
> hints to attackers when working on sensible fields that have a
> non-fixed size.
> 2) Switch at relation level to control wal_compression. This needs to
> change XLogRecordAssemble by adding some new logic to check if a
> relation is enforcing WAL compression or not. As a reloption, there
> are three possible values: true, false and fallback to system default.
> Also, I think that we should simply extend XLogRegisterBuffer() and
> pass to it the reloption flag that is then registered in
> registered_buffer, and XLogRecordAssemble() decides with this flag if
> block is compressed or not. Do we want to add this reloption switch to
> indexes as well? Or only tables? For indexes things will get heavier
> as we would need to add a parameter for all the index types.

After looking at reloptions.c, what we are going to need as well is a
new relopt_type, like RELOPT_TYPE_ENUM for this purpose to be able to
define the 'default' value. We could as well have things using
RELOPT_TYPE_STRING. Any input on this matter is welcome.
--
Michael