from the doc:
The remote transaction uses SERIALIZABLE isolation level when the local transaction has SERIALIZABLE isolation level; otherwise it uses REPEATABLE READ isolation level. This choice ensures that if a query performs multiple table scans on the remote server, it will get snapshot-consistent results for all the scans. A consequence is that successive queries within a single transaction will see the same data from the remote server, even if concurrent updates are occurring on the remote server due to other activities. That behavior would be expected anyway if the local transaction usesSERIALIZABLE or REPEATABLE READ isolation level, but it might be surprising for a READ COMMITTED local transaction. A future PostgreSQL release might modify these rules.
now It can be set to REPEATABLE READ or higher level，and can't be lower level.
from the src code :
362 /*
363 * Start remote transaction or subtransaction, if needed.
364 *
365 * Note that we always use at least REPEATABLE READ in the remote session.
366 * This is so that, if a query initiates multiple scans of the same or
367 * different foreign tables, we will get snapshot-consistent results from
368 * those scans. A disadvantage is that we can't provide sane emulation of
369 * READ COMMITTED behavior --- it would be nice if we had some other way to
370 * control which remote queries share a snapshot.
371 */
372 static void
373 begin_remote_xact(ConnCacheEntry *entry)
374 {
375 int curlevel = GetCurrentTransactionNestLevel();
377 /* Start main transaction if we haven't yet */
378 if (entry->xact_depth <= 0)
379 {
380 const char *sql;
382 elog(DEBUG3, "starting remote transaction on connection %p",
383 entry->conn);
385 if (IsolationIsSerializable())
386 sql = "START TRANSACTION ISOLATION LEVEL SERIALIZABLE";
387 else
388 sql = "START TRANSACTION ISOLATION LEVEL REPEATABLE READ";
389 do_sql_command(entry->conn, sql);
390 entry->xact_depth = 1;
391 }
it is hard code,so you can modify the code to add READ COMMIT level.but be carefull the code comment.
Jov
blog: http:amutu.com/blog
2013/7/11 guxiaobo1982 <guxiaobo1982@xxxxxx>
Hi,We are try to connect to Greenplum database from PostgreSQL 9.3 beta2 via postgres_fdw, but the Greenplum Database does not support REPEATABLE READ transactions, can we specify other isolation leves?Regards,
Xiaobo Gu
