sqlalchemy.dialects.postgresql.asyncpg

Warning

The asyncpg database driver necessarily uses caches for PostgreSQL type OIDs, which become stale when custom PostgreSQL datatypes such as ENUM objects are changed via DDL operations. Additionally, prepared statements themselves which are optionally cached by SQLAlchemy's driver as described above may also become "stale" when DDL has been emitted to the PostgreSQL database which modifies the tables or other objects involved in a particular prepared statement.

The SQLAlchemy asyncpg dialect will invalidate these caches within its local process when statements that represent DDL are emitted on a local connection, but this is only controllable within a single Python process / database engine. If DDL changes are made from other database engines and/or processes, a running application may encounter asyncpg exceptions InvalidCachedStatementError and/or InternalServerError("cache lookup failed for type <oid>") if it refers to pooled database connections which operated upon the previous structures. The SQLAlchemy asyncpg dialect will recover from these error cases when the driver raises these exceptions by clearing its internal caches as well as those of the asyncpg driver in response to them, but cannot prevent them from being raised in the first place if the cached prepared statement or asyncpg type caches have gone stale, nor can it retry the statement as the PostgreSQL transaction is invalidated when these errors occur.