Function SPI_ReserveMemory

src/backend/executor/spi.c:3497–3510

* Push memory reserved for next SPI call. It is possible for an operator to (after several levels of nesting), * result in execution of SQL statements via SPI e.g. a pl/pgsql function that issues queries. These queries must be sandboxed into * the memory limits of the operator. This stack represents the nesting of these operators and each * operator will push its own limit. */

 * operator will push its own limit.
 */
void SPI_ReserveMemory(uint64 mem_reserved)
{
	Assert(!IsResManagerMemoryPolicyNone());
	if (mem_reserved > 0
			&& (SPIMemReserved == 0 || mem_reserved < SPIMemReserved))
	{
		SPIMemReserved = mem_reserved;
	}

	if (LogResManagerMemory())
	{
		elog(GP_RESMANAGER_MEMORY_LOG_LEVEL, "SPI memory reservation %d", (int) SPIMemReserved);
	}
}

/**
 * What was the amount of memory reserved for the last operator? See SPI_ReserveMemory()