Re: [PATCH] Compression dictionaries for JSONB

Hi Matthias,

> The bulk of the patch
> should still be usable, but I think that the way it interfaces with
> the CREATE TABLE (column ...) APIs would need reworking to build on
> top of the api's of the "pluggable toaster" patches (so, creating
> toasters instead of types). I think that would allow for an overall
> better user experience and better performance due to decreased need
> for fully decompressed type casting.

Many thanks for the feedback.

The "pluggable TOASTer" patch looks very interesting indeed. I'm
currently trying to make heads and tails of it and trying to figure
out if it can be used as a base for compression dictionaries,
especially for implementing the partial decompression. Hopefully I
will be able to contribute to it and to the dependent patch [1] in the
upcoming CF, at least as a tester/reviewer. Focusing our efforts on
[1] for now seems to be a good strategy.

My current impression of your idea is somewhat mixed at this point though.

Teodor's goal is to allow creating _extensions_ that implement
alternative TOAST strategies, which use alternative compression
algorithms and/or use the knowledge of the binary representation of
the particular type. For sure, this would be a nice thing to have.
However, during the discussion of the "compression dictionaries" RFC
the consensus was reached that the community wants to see it as a
_built_in_ functionality rather than an extension. Otherwise we could
simply add ZSON to /contrib/ as it was originally proposed.

So if we are going to keep "compression dictionaries" a built-in
functionality, putting artificial constraints on its particular
implementation, or adding artificial dependencies of two rather
complicated patches, is arguably a controversial idea. Especially
considering the fact that it was shown that the feature can be
implemented without these dependencies, in a very non-invasive way.

These are just my initial thoughts I would like to share though. I may
change my mind after diving deeper into a "pluggable TOASTer" patch.

I cc:'ed Teodor in case he would like to share his insights on the topic.

[1]: https://commitfest.postgresql.org/38/3479/

--
Best regards,
Aleksander Alekseev