I see that design question for PostgreSQL pluggable storages is very hard.
IMHO it's mostly expected to be hard.
Firstly, PostgreSQL is a mature product with many advanced features, and reworking a low-level feature without breaking something on top of it is hard by definition.
Secondly, project policies and code quality requirements set the bar very high too, I think.
Sure.
> BTW, I think it worth analyzing existing use-cases of pluggable
storages. I think that the most famous DBMS with pluggable storage API is MySQL. This why I decided to start with it. I've added MySQL/MariaDB section on wiki page. https://wiki.postgresql.org/wiki/Future_of_storage#MySQL.2FMariaDB It appears that significant part of MySQL storage engines are misuses. MySQL lacks of various features like FDWs or writable views and so on. This is why developers created a lot of pluggable storages for that purposes. We definitely don't want something like this in PostgreSQL now. I created special resume column where I expressed whether it would be nice to have something like this table engine in PostgreSQL.
I don't want to discourage you, but I'm not sure how valuable this is.
I agree it's valuable to have a an over-view of use cases for pluggable storage, but I don't think we'll get that from looking at MySQL. As you noticed, most of the storage engines are misuses, so it's difficult to learn anything valuable from them. You can argue that using FDWs to implement alternative storage engines is a misuse too, but at least that gives us a valid use case (columnar storage implemented using FDW).
If anything, the MySQL storage engines should serve as a cautionary tale how not to do things - there's also a plenty of references in the MySQL "Restrictions and Limitations" section of the manual:
Just to clarify the thing. I don't propose any adoption of MySQL pluggable storage API to PostgreSQL or something like this. I just wrote this table for completeness of vision. It may appear that somebody will make some valuable notes out of it, it may appear that not. "Yes" in third column means only that there is positive user visible effects which are *nice to have* in PostgreSQL.
Also, I remember there was a table with comparison of different designs of pluggable storages and their use-cases at PGCon 2017 unconference. Could somebody reproduce it?
------ Alexander Korotkov Postgres Professional: http://www.postgrespro.com The Russian Postgres Company