ab13c46ff4
Commit 2dc1deaea turns out to have been still a brick shy of a load, because CALL statements executing within a plpgsql exception block could still pass the wrong snapshot to stable functions within the CALL's argument list. That happened because standard_ProcessUtility forces isAtomicContext to true if IsTransactionBlock is true, which it always will be inside a subtransaction. Then ExecuteCallStmt would think it does not need to push a new snapshot --- but _SPI_execute_plan didn't do so either, since it thought it was in nonatomic mode. The best fix for this seems to be for _SPI_execute_plan to operate in atomic execution mode if IsSubTransaction() is true, even when the SPI context as a whole is non-atomic. This makes _SPI_execute_plan have the same rules about when non-atomic execution is allowed as _SPI_commit/_SPI_rollback have about when COMMIT/ROLLBACK are allowed, which seems appropriately symmetric. (If anyone ever tries to allow COMMIT/ROLLBACK inside a subtransaction, this would all need to be rethought ... but I'm unconvinced that such a thing could be logically consistent at all.) For further consistency, also check IsSubTransaction() in SPI_inside_nonatomic_context. That does not matter for its one present-day caller StartTransaction, which can't be reached inside a subtransaction. But if any other callers ever arise, they'd presumably want this definition. Per bug #18656 from Alexander Alehin. Back-patch to all supported branches, like previous fixes in this area. Discussion: https://postgr.es/m/18656-cade1780866ef66c@postgresql.org
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