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Reset Connection._top_xact when BEGIN fails in Transaction.start() #1387

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Reset Connection._top_xact when BEGIN fails in Transaction.start() #1387

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f895d1c
tests: Cover a failed BEGIN in Transaction.start()
devtechedge Oct 7, 2026
a7100fa
Reset Connection._top_xact when BEGIN fails in Transaction.start()
devtechedge Oct 7, 2026
af00698
tests: Stub execute so a failed BEGIN does not race the loop
devtechedge Oct 7, 2026
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2 changes: 2 additions & 0 deletions asyncpg/transaction.py
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Original file line number Diff line number Diff line change
Expand Up @@ -146,6 +146,8 @@ async def start(self):
await self._connection.execute(query)
except BaseException:
self._state = TransactionState.FAILED
if con._top_xact is self:
con._top_xact = None
raise
else:
self._state = TransactionState.STARTED
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25 changes: 25 additions & 0 deletions tests/test_transaction.py
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Expand Up @@ -5,6 +5,8 @@
# the Apache 2.0 License: http://www.apache.org/licenses/LICENSE-2.0


import asyncio

import asyncpg

from asyncpg import _testbase as tb
Expand Down Expand Up @@ -180,6 +182,29 @@ async def test_transaction_within_manual_transaction(self):
self.assertIsNone(self.con._top_xact)
self.assertFalse(self.con.is_in_transaction())

async def test_transaction_failed_begin(self):
self.assertIsNone(self.con._top_xact)

# Make BEGIN fail by running it while another
# operation is in progress on the connection.
busy = asyncio.ensure_future(self.con.execute('SELECT pg_sleep(0.5)'))
await asyncio.sleep(0.1)
with self.assertRaisesRegex(asyncpg.InterfaceError,
'another operation is in progress'):
await self.con.transaction().start()
await busy

@elprans elprans Oct 7, 2026

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Can we do something like this to avoid relying on flaky loop timing?

Suggested change
# Make BEGIN fail by running it while another
# operation is in progress on the connection.
busy = asyncio.ensure_future(self.con.execute('SELECT pg_sleep(0.5)'))
await asyncio.sleep(0.1)
with self.assertRaisesRegex(asyncpg.InterfaceError,
'another operation is in progress'):
await self.con.transaction().start()
await busy
tr = self.con.transaction()
error = asyncpg.PostgresConnectionError(
'Timed-out waiting to acquire database connection.'
)
with mock.patch.object(
type(self.con), 'execute', side_effect=error
) as execute:
with self.assertRaises(asyncpg.PostgresConnectionError) as caught:
await tr.start()
self.assertIs(caught.exception, error)
execute.assert_awaited_once_with('BEGIN;')

@devtechedge devtechedge Oct 7, 2026

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Thanks for catching that, Elvis.

The sleep was a bad way to force BEGIN to fail, and a slow loop could miss the window.

I switched the test to patch execute with a PostgresConnectionError, the way you suggested.

It still checks that _top_xact is cleared and that the next transaction() is a real top-level one, because those are the checks that fail without the fix.

The mock only wraps start(), so that follow-up runs on the live connection.

Happy to trim it if you'd rather the test stop where your suggestion did.


self.assertIsNone(self.con._top_xact)
self.assertFalse(self.con.is_in_transaction())

# The next transaction must be a real top-level one.
async with self.con.transaction():
self.assertTrue(self.con.is_in_transaction())
await self.con.execute('SELECT 1')

self.assertIsNone(self.con._top_xact)
self.assertFalse(self.con.is_in_transaction())

async def test_isolation_level(self):
await self.con.reset()
default_isolation = await self.con.fetchval(
Expand Down