Function postgresExecForeignTruncate

contrib/postgres_fdw/postgres_fdw.c:2974–3064

* postgresExecForeignTruncate * Truncate one or more foreign tables */

 *		Truncate one or more foreign tables
 */
static void
postgresExecForeignTruncate(List *rels,
							DropBehavior behavior,
							bool restart_seqs)
{
	Oid			serverid = InvalidOid;
	UserMapping *user = NULL;
	PGconn	   *conn = NULL;
	StringInfoData sql;
	ListCell   *lc;
	bool		server_truncatable = true;

	/*
	 * By default, all postgres_fdw foreign tables are assumed truncatable.
	 * This can be overridden by a per-server setting, which in turn can be
	 * overridden by a per-table setting.
	 */
	foreach(lc, rels)
	{
		ForeignServer *server = NULL;
		Relation	rel = lfirst(lc);
		ForeignTable *table = GetForeignTable(RelationGetRelid(rel));
		ListCell   *cell;
		bool		truncatable;

		/*
		 * First time through, determine whether the foreign server allows
		 * truncates. Since all specified foreign tables are assumed to belong
		 * to the same foreign server, this result can be used for other
		 * foreign tables.
		 */
		if (!OidIsValid(serverid))
		{
			serverid = table->serverid;
			server = GetForeignServer(serverid);

			foreach(cell, server->options)
			{
				DefElem    *defel = (DefElem *) lfirst(cell);

				if (strcmp(defel->defname, "truncatable") == 0)
				{
					server_truncatable = defGetBoolean(defel);
					break;
				}
			}
		}

		/*
		 * Confirm that all specified foreign tables belong to the same
		 * foreign server.
		 */
		Assert(table->serverid == serverid);

		/* Determine whether this foreign table allows truncations */
		truncatable = server_truncatable;
		foreach(cell, table->options)
		{