Trying to debug `asyncpg.exceptions._base.InterfaceError: cannot perform operation: another operation is in progress`

• asyncpg version: 0.20.1
• PostgreSQL version: 12
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: no
• Python version: 3.7.5
• Platform: OS X
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: yes
• If you built asyncpg locally, which version of Cython did you use?: -
• Can the issue be reproduced under both asyncio and
  uvloop?: yes

Hi!

I'm trying to debug an issue that I have with errors like asyncpg.exceptions._base.InterfaceError: cannot perform operation: another operation is in progress from this line: https://github.com/MagicStack/asyncpg/blob/dcef29804095990f25178b642b920f3fbcb4ca22/asyncpg/protocol/protocol.pyx#L664

I am trying to understand where I could have gone wrong. So, I would like to ask the following preliminary question:

Suppose my code interacts with asyncpg only through a pool, and only using context managers:

async with pool.acquire() as connection:
     ...

I also do not share the connection object around. On it, I use the methods fetchrow, fetchval and fetch. They are used sequentially from the same asyncio "thread" (for lack of better word). That is to say, they are never called in parallel.

In this setup, I would think that the error cannot perform operation: another operation is in progress never shows up, but it does. Am I missing something?

Start by reading asyncpg/protocol/protocol.pyx around line 664, then trace the pool.acquire context and the sequential fetchrow, fetchval, and fetch calls described in the report. Try to reduce the behavior to a reproducible example under asyncio and uvloop. Done means identifying the conflicting operation or documenting the missing reproduction details needed to diagnose it.