Support CrateDB

[felixge]

See #320

@jackc I spend a decent amount of time trying to come up with a minimally invasive patch and added some detailed in-line comments explaining my approach. Let me know what you think.

[jackc]

Thanks! Looks like as clean and narrow a change as we could hope for.

[felixge]

Thanks a lot! I'll be around to help if anybody runs into any unexpected issues with this.

[mfussenegger]

Nice to see CrateDB support in pgx.

One question to the pg_type query: Would it be possible to change this in
pgx to query explicitly on pg_catalog.pg_type?
I'm not sure if this could break anything with older postgres versions. Afaik
9+ should be fine.

It would be fairly simple for us to add the typtype column, but extending the
schema lookup logic is a bit more work.

The reason I'm asking is that this way we could add typtype and then no
longer have to worry about breaking anything here if we change something with
the error codes / error messages.

[felixge]

@mfussenegger not sure about @jackc, but from my POV changing the query to explicitly target the pg_catalog schema should be a reasonable change. As far as I can tell the pg_catalog schema has been around and can be explicitly specified in queries since at least Postgres 7.3.

That being said, I think the workaround code should probably still need to stay in place to support older CrateDB versions for a while.

[jackc]

No objections from me for explicitly qualifying the pg_catalog schema.

[felixge]

@mfussenegger let me know when typtype gets implemented in CrateDB (is there a GH issue to subscribe to?). Then I'll do the PR and testing for pgx.

[mfussenegger]

@felixge We've added the column (see crate/crate#6582) - will be part of 2.3 (or in the nightly builds starting tomorrow)

[felixge]

@mfussenegger cool. I'm traveling for the next three weeks, but I'll try to find some time to make a PR for this ASAP.