What can go wrong with implicit I/O or concurrent tasks using SQLAlchemy AsyncSession?

Makes AsyncSession transaction ownership and every database I/O point explicit.

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An AsyncSession represents mutable state for one transaction and is not safe to share across concurrent tasks. Passing it to several operations inside asyncio.gather() can interleave transaction and connection state. Async ORM code also cannot safely trigger arbitrary database work through ordinary attribute access. A lazy or expired relationship can therefore raise MissingGreenlet when SQLAlchemy attempts I/O outside the expected awaitable path.

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Makes AsyncSession transaction ownership and every database I/O point explicit.

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Makes AsyncSession transaction ownership and every database I/O point explicit.
An AsyncSession represents mutable state for one transaction and is not safe to share across concurrent tasks. Passing it to several operations inside asyncio.gather() can interleave transaction and connection state. Async ORM code also cannot safely trigger arbitrary database work through ordinary attribute access. A lazy or expired relationship can therefore raise MissingGreenlet when SQLAlchemy attempts I/O outside the expected awaitable path.
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I give each concurrent task its own AsyncSession, or keep related database steps sequential in one transaction. I load required relationships explicitly with select-in or joined strategies, use explicit refresh or awaitable attributes where justified, and often set for a well-defined async session factory. That setting prevents automatic expiration after commit; it does not make stale objects current or sessions concurrency-safe.

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Sharing one AsyncSession through gather
Allowing lazy I/O during serialization
Assuming separate sessions share one transaction

What can go wrong with implicit I/O or concurrent tasks using SQLAlchemy AsyncSession?

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