MagicStack / MagicStack/asyncpg

getaddrinfo() error / exception not re-raised?

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Python
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Description

  • asyncpg version: 0.22
  • PostgreSQL version:
  • Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
    the issue with a local PostgreSQL install?
    :
  • Python version: 3.8
  • Platform: linux ubuntu 20.04
  • Do you use pgbouncer?:nope
  • Did you install asyncpg with pip?:yes
  • If you built asyncpg locally, which version of Cython did you use?:no
  • Can the issue be reproduced under both asyncio and
    uvloop?
    : Did not test

Potential slight bug?
I have an asyncio loop with a task that sequentially pops queries from an asyncio queue to execute, one at a time, in a remote timescaleDB (postgresql) database. Everything works like a charm. And I'd rather say quite performant!

But, whenever I unplug the ethernet cable of query requester (to simulate sudden connection losses), an uncatched exception error pops up related to the impossibility to resolve the name address of the DSN
: 2021-09-10 10:10:44.846 ERROR: Future exception was never retrieved
: future: <Future finished exception=gaierror(-3, 'Temporary failure in name resolution')>
: Traceback (most recent call last):
: File "/home/venv/lib/python3.8/site-packages/asyncpg/connection.py", line 1393, in _cancel
: await connect_utils._cancel(
: File "/home/venv/lib/python3.8/site-packages/asyncpg/connect_utils.py", line 696, in _cancel
: tr, pr = await _create_ssl_connection(
: File "/home/venv/lib/python3.8/site-packages/asyncpg/connect_utils.py", line 544, in _create_ssl_connection
: tr, pr = await loop.create_connection(
: File "/usr/lib/python3.8/asyncio/base_events.py", line 986, in create_connection
: infos = await self._ensure_resolved(
: File "/usr/lib/python3.8/asyncio/base_events.py", line 1365, in _ensure_resolved
: return await loop.getaddrinfo(host, port, family=family, type=type,
: File "/usr/lib/python3.8/asyncio/base_events.py", line 825, in getaddrinfo
: return await self.run_in_executor(
: File "/usr/lib/python3.8/concurrent/futures/thread.py", line 57, in run
: result = self.fn(*self.args, **self.kwargs)
: File "/usr/lib/python3.8/socket.py", line 918, in getaddrinfo
: for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
: socket.gaierror: [Errno -3] Temporary failure in name resolution

I have the execute() code within a try: / exception: block. Amongst the several exceptions i trap i have the generic exception Exception. But this is of no use because this error is not re raised and keeps within the asyncpg library.

Shouldn't it be re raised so that the app deals with that issue?

Thank you for this fantastic library!

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reading asyncpg/connection.py around _cancel and asyncpg/connect_utils.py around _cancel and _create_ssl_connection, then reproduce the reported DNS failure while a connection is active. Trace how the gaierror is handled and whether the cancellation future is observed. Done means the failure behavior is covered by a regression test and the resulting exception is delivered to the application rather than reported as an unretrieved future exception.

Written by the indexing model from the issue text.

Assessment

Tech stack
postgresql, python
Domain
database
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
42/100

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