Re: toast by chunk-end (was Re: PG_PAGE_LAYOUT_VERSION 5 - time for change)

Zdenek Kotala wrote:
> Heikki Linnakangas napsal(a):
>> Zdenek Kotala wrote:
>>> Just a very quick look on your patch. See my comments:
>>>
>>> ...
>>>
>>> 2) PG_PAGE_LAYOUT_VERSION should be bump
>>
>> The patch doesn't change the page layout AFAICS.
>>
>
> It is good question what is and what is not page layout. I think that
> toast implementation is a member of page layout. OK it is called page
> layout but better name should be On Disk Format (ODF). You will not able
> to read 8.3 toasted table in 8.4.

It's clearly just a catalog change; the number and meaning of attributes
has changed, and that's reflected in CATALOG_VERSION_NO.

We need to be pragmatic, though, and think about how the conversion
would work, and if the version number change would help or hurt that
process. I'm not clear how we would handle the toast table change. If
we're going to handle it by retoasting all attributes when the main heap
page is read in, then I suppose we'd actually change the version number
of the *heap* page, not toast table pages, when the heap page is
retoasted. However, if you want to do it toast-page at a time, or
toast-tuple at a time, you can just look at the number of attributes on
the toast tuple to determine which format it's in.

Note that bumping the version number is not free. We haven't made any
changes in 8.4 this far that would require bumping it. If we do bump it,
the next version with online-upgrade support will need to deal with it,
if only to increment and write back the page.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com