Re: pg_upgrade: convert on read is dead end

Heikki Linnakangas napsal(a):
> Zdenek Kotala wrote:
>> Heikki Linnakangas napsal(a):
>>> Besides, the "read all formats" approach wouldn't really avoid it 
>>> either. If you passed a toasted datum to a function, when the 
>>> function needs to detoast it, detoast_datum still wouldn't know 
>>> whether the datum is in old or new format. You'd still need to 
>>> detoast all values in the tuple somewhere before they could be passed 
>>> around.
>>
>> If you look into pg_upgrade prototype patch I added page version 
>> information into HeapTupleData structure. It keeps information about 
>> format. All chunked data are stored on a pages with same page 
>> versions. I think these two things are enough to have all necessary 
>> information.
> 
> Functions are passed just a Datum, not HeapTupleData.
> 

But executor works with HeapTupleData structure and it should convert it to the 
new format before it passes it to function. My idea is to convert tuple in 
ExecTupleStore or invent new node special for tuple conversion.

I expect that function cannot get toast pointer. It can get only detoasted 
attributes. Correct me if I'm wrong.        Zdenek

-- 
Zdenek Kotala              Sun Microsystems
Prague, Czech Republic     http://sun.com/postgresql