Re: Proposal: Multiversion page api (inplace upgrade)

Heikki Linnakangas wrote:
> 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.

I understand the goal of having good modularity (not having ReadBuffer
modify the page), but I am worried that doing multi-version page
processing in a modular way is going to spread version-specific
information all over the backend code, making is harder to understand.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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