Re: pg_upgrade: How to deal with toast

Heikki Linnakangas napsal(a):
> Zdenek Kotala wrote:
>> The question is if we should do toast modification now to avoid 
>> potential future problems or if we will solve it when any on-disk 
>> format change requires it?
> 
> Perhaps we should just add the new attid attribute to the toast table, 
> but mark it as nullable? We wouldn't need to fill it in in the 8.3->8.4 
> conversion but new tuples would include it.>
> In the future release that we actually need it, we'll make it 
> non-nullable, and write a pre-upgrade script to retoast tuples that 
> don't have it yet.

Hmm, It seems to me as a good idea. It will complicated preupgrade script for 
8.4->8.5 script but we will have one year to developed it :-).

What we need to do is during conversion to add nullbit array for each tuple in 
toasttable. I think there is enough space on all platform to reuse gap between 
tuple header and data.

> Hmm. That would change TOAST_MAX_CHUNK_SIZE, though.

Yes, it change it. :(

but I can convert easily residx to offset end (residx*TOAST_MAX_CHUNK_SIZE -+ 
something) during page conversion.

>> I prefer do it now, because there could be small risk that it will not 
>> possible to do it in the future. When in-place upgrade will be 
>> implemented nobody will want to perform backup/restore.
> 
> I feel we should avoid doing anything extra, risking that we get nothing 
> finished.

Agree.
    Zdenek