Add configuration to skip querying of comp_oids

[jeregrine]

It is becoming more common to use the "postgres wire protocol" for non-postgres projects. Many of these projects "support" the basic type bootstrap query, but do not support the Array+subquery syntax nor custom types.

I added a configuration option to pass to the repo/start_link that enables this:

skip_comp_oids: true|false

Appears to work in my test cases but its pretty difficult to write an actual test for this without mocking the connection? Any guidance would be helpful.

[josevalim]

If we skip comp_oids, it means we will be unable to encode/decode records. If we want to go down this route, I think this option should be called "disable_composite_types". :)

[jeregrine]

If we skip comp_oids, it means we will be unable to encode/decode records. If we want to go down this route, I think this option should be called "disable_composite_types". :)

sounds good, I'll change it on monday. I don't think people using postgrex for its wire protocol care too much about records or custom types at all.

[greg-rychlewski]

Is it just turning subquery results into an array or do these databases not support arrays at all? I was thinking it might be worth benchmarking a join with array_agg, if that is generally supported?

[jeregrine]

Its not 100% clear to me, it seems that cockroachdb struggled with the comp oids subquery as well as some sqlite implementations that I saw. In these cases the likelihood they support records is low. As far as I can tell go/rust libs did not have this issue cause they compile default oids into the lib unless a type is defined.

[jeregrine]

@josevalim changes made.

[josevalim]

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