Re: Pluggable toaster

Hi Nikita,

> >I don't argue with most of what you say. I am just pointing out the
> >reason why the chosen approach "N TOASTers x M TableAMs" will not
> >work:
>
> We assume that TAM used in custom Toaster works as it is should work,
> and leave TAM internals to this TAM developer - say, we do not want to
> change internals of Heap AM.
>
> We don't want to create some kind of silver bullet.

This is exactly the point. In order to not to create a silver bullet,
TOASTers should be limited to a single TableAM. The one we know uses
pages of a known fixed size, the one that actually requires TOAST
because pages are relatively small, etc.

> That's what the TOAST API is - just an interface that all custom
> TOAST implementations use to have a common entry point from any TAM,
> [...]

I believe this is the source of misunderstanding. Note that not _any_
TableAM needs TOAST to begin with. As an example, if one chooses to
implement a column-organized TableAM that stores all text/bytea
attributes in a separate dictionary file this person doesn't need
TOAST and doesn't want to be constrained by the need of choosing one.

For this reason the "N TOASTers x M TableAMs" approach is
architecturally broken.

> keep in mind that different kinds of data require very
> different approach to external storage - say, JSON TOAST works with
> maps of keys and values, [...]

To clarify: is an ability to specify TOASTers for given columns and/or
types also part of the plan?

> Have I answered your question? Please don't hesitate to point to any unclear
> parts, I'd be glad to explain that.

No. To be honest, it looks like you are merely discarding most/any
feedback the community provided so far.

I really think that pluggable TOASTers would be a great feature.
However if the goal is to get it into the core I doubt that we are
going to make much progress with the current approach.

-- 
Best regards,
Aleksander Alekseev