Can a Postgres Commit Exist in Procedure that has an Exception Block?

Question

I am having a difficult time understanding transactions in Postgres. I have a procedure that may encounter an exception. There are parts of the procedure where I might want

Answer 1

The problem is the EXCEPTION clause.

This is implemented in PL/pgSQL as a subtransaction (the same thing as a SAVEPOINT in SQL), which is rolled back when the exception block is reached.

You cannot COMMIT while a subtransaction is active.

See this comment in src/backend/executor/spi.c:

/*
 * This restriction is required by PLs implemented on top of SPI.  They
 * use subtransactions to establish exception blocks that are supposed to
 * be rolled back together if there is an error.  Terminating the
 * top-level transaction in such a block violates that idea.  A future PL
 * implementation might have different ideas about this, in which case
 * this restriction would have to be refined or the check possibly be
 * moved out of SPI into the PLs.
 */
if (IsSubTransaction())
    ereport(ERROR,
            (errcode(ERRCODE_INVALID_TRANSACTION_TERMINATION),
             errmsg("cannot commit while a subtransaction is active")));