Since I cannot get the value of transaction_read_only via PQparameterStatus.
Hmmm... we can at least get default_transaction_read_only. As fe-connect.c points out:
/*
* "transaction_read_only = on" proves that at least one * of default_transaction_read_only and in_hot_standby is * on, but we don't actually know which. We don't care * though for the purpose of identifying a read-only * session, so satisfy the CONNECTION_CHECK_TARGET code by * claiming they are both on. On the other hand, if it's * a read-write session, they are certainly both off. */
Maybe that's good enough? It won't detect people starting a new transaction and declaring it read-only, but it should be sufficient to warn people when a connection is starting out in a read-only state. And it will still toggle auto-magically on promotion.
