Function postgresAnalyzeForeignTable

contrib/postgres_fdw/postgres_fdw.c:4936–4992

* postgresAnalyzeForeignTable * Test whether analyzing this foreign table is supported */

 *		Test whether analyzing this foreign table is supported
 */
static bool
postgresAnalyzeForeignTable(Relation relation,
							AcquireSampleRowsFunc *func,
							BlockNumber *totalpages)
{
	ForeignTable *table;
	UserMapping *user;
	PGconn	   *conn;
	StringInfoData sql;
	PGresult   *volatile res = NULL;

	/* Return the row-analysis function pointer */
	*func = postgresAcquireSampleRowsFunc;

	/*
	 * Now we have to get the number of pages.  It's annoying that the ANALYZE
	 * API requires us to return that now, because it forces some duplication
	 * of effort between this routine and postgresAcquireSampleRowsFunc.  But
	 * it's probably not worth redefining that API at this point.
	 */

	/*
	 * Get the connection to use.  We do the remote access as the table's
	 * owner, even if the ANALYZE was started by some other user.
	 */
	table = GetForeignTable(RelationGetRelid(relation));
	user = GetUserMapping(relation->rd_rel->relowner, table->serverid);
	conn = GetConnection(user, false, NULL);

	/*
	 * Construct command to get page count for relation.
	 */
	initStringInfo(&sql);
	deparseAnalyzeSizeSql(&sql, relation);

	/* In what follows, do not risk leaking any PGresults. */
	PG_TRY();
	{
		res = pgfdw_exec_query(conn, sql.data, NULL);
		if (PQresultStatus(res) != PGRES_TUPLES_OK)
			pgfdw_report_error(ERROR, res, conn, false, sql.data);

		if (PQntuples(res) != 1 || PQnfields(res) != 1)
			elog(ERROR, "unexpected result from deparseAnalyzeSizeSql query");
		*totalpages = strtoul(PQgetvalue(res, 0, 0), NULL, 10);
	}
	PG_FINALLY();
	{
		if (res)
			PQclear(res);
	}
	PG_END_TRY();

	ReleaseConnection(conn);

	return true;
}