Function GetConnection

contrib/postgres_fdw/connection.c:124–278

* Get a PGconn which can be used to execute queries on the remote PostgreSQL * server with the user's authorization. A new connection is established * if we don't already have a suitable one, and a transaction is opened at * the right subtransaction nesting depth if we didn't do that already. * * will_prep_stmt must be true if caller intends to create any prepared * statements. Since those

 * with the PGconn.
 */
PGconn *
GetConnection(UserMapping *user, bool will_prep_stmt, PgFdwConnState **state)
{
	bool		found;
	bool		retry = false;
	ConnCacheEntry *entry;
	ConnCacheKey key;
	MemoryContext ccxt = CurrentMemoryContext;

	/* First time through, initialize connection cache hashtable */
	if (ConnectionHash == NULL)
	{
		HASHCTL		ctl;

		ctl.keysize = sizeof(ConnCacheKey);
		ctl.entrysize = sizeof(ConnCacheEntry);
		ConnectionHash = hash_create("postgres_fdw connections", 8,
									 &ctl,
									 HASH_ELEM | HASH_BLOBS);

		/*
		 * Register some callback functions that manage connection cleanup.
		 * This should be done just once in each backend.
		 */
		RegisterXactCallback(pgfdw_xact_callback, NULL);
		RegisterSubXactCallback(pgfdw_subxact_callback, NULL);
		CacheRegisterSyscacheCallback(FOREIGNSERVEROID,
									  pgfdw_inval_callback, (Datum) 0);
		CacheRegisterSyscacheCallback(USERMAPPINGOID,
									  pgfdw_inval_callback, (Datum) 0);
	}

	/* Set flag that we did GetConnection during the current transaction */
	xact_got_connection = true;

	/* Create hash key for the entry.  Assume no pad bytes in key struct */
	key = user->umid;

	/*
	 * Find or create cached entry for requested connection.
	 */
	entry = hash_search(ConnectionHash, &key, HASH_ENTER, &found);
	if (!found)
	{
		/*
		 * We need only clear "conn" here; remaining fields will be filled
		 * later when "conn" is set.
		 */
		entry->conn = NULL;
	}

	/* Reject further use of connections which failed abort cleanup. */
	pgfdw_reject_incomplete_xact_state_change(entry);

	/*
	 * If the connection needs to be remade due to invalidation, disconnect as
	 * soon as we're out of all transactions.
	 */