Re: [REVIEW] Re: Compression of full-page-writes

On Tue, Dec 2, 2014 at 7:16 PM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> In the latest versions of the patch, control of compression is done
> within full_page_writes by assigning a new value 'compress'. Something
> that I am scared of is that if we enforce compression when
> full_page_writes is off for forcibly-written pages and if a bug shows
> up in the compression/decompression algorithm at some point (that's
> unlikely to happen as this has been used for years with toast but
> let's say "if"), we may corrupt a lot of backups. Hence why not simply
> having a new GUC parameter to fully control it. First versions of the
> patch did that but ISTM that it is better than enforcing the use of a
> new feature for our user base.

That's a very valid concern. But maybe it shows that
full_page_writes=compress is not the Right Way To Do It, because then
there's no way for the user to choose the behavior they want when
full_page_writes=off but yet a backup is in progress. If we had a
separate GUC, we could know the user's actual intention, instead of
guessing.

--
Robert Haas
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