Re: Proposal: Multiversion page api (inplace upgrade)

Zdenek Kotala wrote:
> 4) Implementation
>
> The main point of implementation is to have several version of
> PageHeader structure (e.g. PageHeader_04, PageHeader_03 ...) and correct
> structure will be handled in special branch (see examples).

(this won't come as a surprise as we talked about this in PGCon, but) I
think we should rather convert the page structure to new format in
ReadBuffer the first time a page is read in. That would keep the changes
a lot more isolated.

Note that you need to handle not only page header changes, but changes
to internal representations of different data types, and changes like
varvarlen and combocid. Those are things that have happened in the past;
in the future, I'm foreseeing changes to the toast header, for example,
as there's been a lot of ideas related to toast options compression.

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