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negative interval encoding issues due to python's timedelta implementation details

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
32/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Stale
Tech stack
postgresql, python
Domain
databases

Research direction

No source file or test is named. Start by reproducing the negative three-hour timedelta case with asyncpg 0.29.0, Python 3.11.7, and PostgreSQL 16.1, then trace the interval encoding and decoding behavior. Done means the expected representation or a documented workaround is established, with regression coverage for negative sub-day intervals.

Written by the indexing model from the issue text.

Description

  • asyncpg version: 0.29.0
  • PostgreSQL version: 16.1
  • Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
    the issue with a local PostgreSQL install?    : this is happening on local PG
  • Python version: 3.11.7
  • Platform:
  • 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

Python's timedelta implementation only allows to store negative number of days, hours, minutes, seconds, microseconds are always positive values. So when a negative value smaller than a day is interpreted it is stored in a strange way, example from Python's documentation:

Note that normalization of negative values may be surprising at first. For example:

>>> from datetime import timedelta
>>> d = timedelta(microseconds=-1)
>>> (d.days, d.seconds, d.microseconds)
(-1, 86399, 999999)

https://docs.python.org/3/library/datetime.html?highlight=timedelta#datetime.timedelta

In my particular case when I'm trying to store -3 hours, that's getting translated in python to:

datetime.timedelta(days=-1, seconds=75600)

And ends up stored in postgresql as: "0 years 0 mons -1 days 21 hours 0 mins 0.0 secs"

Is there also a workaround where I can skip timedelta for interval?

Dominant language
Python
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Merged PRs (30d)
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