• asyncpg version: 0.20.1
• PostgreSQL version: 12.1
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: postgresql is installed locally on archlinux
• Python version: 3.7.6 and 3.8.1
• Platform: Linux 5.4.13-arch1-1
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: yes
• If you built asyncpg locally, which version of Cython did you use?: N/A
• Can the issue be reproduced under both asyncio and
  uvloop?: yes

I have a few custom types (CREATE TYPE ...) in my database, and I'm running into issues where asyncpg's introspection stage on queries using 2 or more of these types are taking > 1 second to complete.

e.g.

add log_min_duration_statement = 500 to the default postgresql.conf

Create a database test with schema:

CREATE TYPE FOURBIGINTS AS (i0 BIGINT, i1 BIGINT, i2 BIGINT, i3 BIGINT); CREATE TYPE NUMBERS_AS_WORDS AS ENUM ( 'zero', 'one', 'two', 'three', 'four' ); CREATE TABLE bigthings ( thing_id BIGSERIAL PRIMARY KEY, num FOURBIGINTS, words NUMBERS_AS_WORDS ); 

and run the following code:

import asyncio import asyncpg async def main(): con_args = { 'dsn': 'postgres:///test', 'ssl': None, 'min_size': 10, 'max_size': 10 } pool = await asyncpg.create_pool(**con_args) async with pool.acquire() as con: await con.execute( """\ INSERT INTO bigthings (num, words) VALUES ($1::FOURBIGINTS, $2::NUMBERS_AS_WORDS) """, (0, 0, 0, 0), 'one') asyncio.run(main()) 

watching the logs (on my system sudo journalctl -u postgresql -f, will show something like:

2020-01-21 14:45:49.066 CET [118544] LOG: duration: 1593.511 ms execute __asyncpg_stmt_2__: WITH RECURSIVE typeinfo_tree( oid, ns, name, kind, basetype, has_bin_io, elemtype, elemdelim, range_subtype, elem_has_bin_io, attrtypoids, attrnames, depth) AS ( SELECT ... 2020-01-21 14:45:49.066 CET [118544] DETAIL: parameters: $1 = '{16584,16582}' 

I've traced this back to the call to _introspect_types in connection.py.

From a bit of testing, it only happens if there are multiple custom types used in the query. e.g. if i change the query to simply be INSERT INTO bigthings (num) VALUES ($1::FOURBIGINTS), then everything is nice and fast as expected, or if i change the bigthings.words column to a VARCHAR, then there is no problem. But as soon as I include two or more custom types (e.g. 2 enum types or 2 tuple types, or a mix) then I see the slow downs.

Is there anything I can do to either remove the need for this introspection (e.g. giving asyncpg some hints about these types), or maybe I'm doing something wrong that I can correct?