Introspection query used for array with native types

[ipeluffo]

Hi all,

I found that asyncpg is running an introspection query which was taking too long causing some issues in a Postgres 12 instance.

After doing some research I found:

1. Slow introspection when using multiple custom types in a query #530
2. https://docs.sqlalchemy.org/en/14/dialects/postgresql.html#disabling-the-postgresql-jit-to-improve-enum-datatype-handling
3. Delay on first access to enum columns using prepared statements #727

However, most (if not all) who complained about this issue use custom types such as enums but in my case, the query is used to introspect array types.

Below is the result of the query run by asyncpg:

+----+----------+--------+----+--------+--------+---------+-------------+-----------+---------+-----+-------------+-----------------+------------------+
|oid |ns        |name    |kind|basetype|elemtype|elemdelim|range_subtype|attrtypoids|attrnames|depth|basetype_name|elemtype_name    |range_subtype_name|
+----+----------+--------+----+--------+--------+---------+-------------+-----------+---------+-----+-------------+-----------------+------------------+
|1043|pg_catalog|varchar |b   |null    |0       |null     |null         |null       |null     |1    |null         |-                |null              |
|2950|pg_catalog|uuid    |b   |null    |0       |null     |null         |null       |null     |1    |null         |-                |null              |
|2951|pg_catalog|_uuid   |b   |null    |2950    |,        |null         |null       |null     |0    |null         |uuid             |null              |
|1015|pg_catalog|_varchar|b   |null    |1043    |,        |null         |null       |null     |0    |null         |character varying|null              |
+----+----------+--------+----+--------+--------+---------+-------------+-----------+---------+-----+-------------+-----------------+------------------+

Then, my questions are:

1. Why does asyncpg need to do introspection of arrays of native types? Is this behaviour expected?
2. Is it possible to register codecs to prevent asyncpg from running the introspection query?

It's worth to mention that I've seen the suggested idea to disable JIT in PG which is an option I'm considering.

Thanks in advance for any help