Re: PG_PAGE_LAYOUT_VERSION 5 - time for change

Heikki Linnakangas  writes:
> Hmm, you're right. I think it can be made to work by storing the *end* 
> offset of each chunk. To find the chunk containing offset X, search for 
> the first chunk with end_offset > X.

Yeah, that seems like it would work, and it would disentangle us
altogether from needing a hard-wired chunk size.  The only downside is
that it'd be a pain to convert in-place.  However, if we are also going
to add identifying information to the toast chunks (like the owning
column's number or datatype), then you could tell whether a toast chunk
had been converted by checking t_natts.  So in principle a toast table
could be converted a page at a time.  If the converted data didn't fit
you could push one of the chunks out to some new page of the file.

On the whole I like this a lot better than Zdenek's original proposal
http://archives.postgresql.org/pgsql-hackers/2008-10/msg00556.php
which didn't seem to me to solve much of anything.
		regards, tom lane