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<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l362>/* 363<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l363> * Start remote transaction or subtransaction, if needed. 364<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l364> * 365<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l365> * Note that we always use at least REPEATABLE READ in the remote session. 366<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l366> * This is so that, if a query initiates multiple scans of the same or 367<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l367> * different foreign tables, we will get snapshot-consistent results from 368<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l368> * those scans. A disadvantage is that we can't provide sane emulation of 369<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l369> * READ COMMITTED behavior --- it would be nice if we had some other way to 370<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l370> * control which remote queries share a snapshot. 371<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l371> */ 372<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l372>static void 373<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l373>begin_remote_xact(ConnCacheEntry *entry) 374<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l374>{ 375<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l375> int curlevel = GetCurrentTransactionNestLevel(); 376<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l376> 377<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l377> /* Start main transaction if we haven't yet */ 378<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l378> if (entry->xact_depth <= 0) 379<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l379> { 380<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l380> const char *sql; 381<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l381> 382<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l382> elog(DEBUG3, "starting remote transaction on connection %p", 383<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l383> entry->conn); 384<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l384> 385<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l385> if (IsolationIsSerializable()) 386<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l386> sql = "START TRANSACTION ISOLATION LEVEL SERIALIZABLE"; 387<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l387> else 388<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l388> sql = "START TRANSACTION ISOLATION LEVEL REPEATABLE READ"; 389<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l389> do_sql_command(entry->conn, sql); 390<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l390> entry->xact_depth = 1; 391<http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/postgres_fdw/connection.c;h=ab098bea3af616c55cc7571936a8448b5b8b40d9;hb=f02b14f787980ac5b2f25407e5cd771e6b1a1dfc#l391> } 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 <http://amutu.com/blog> 2013/7/11 guxiaobo1982 <guxiaobo1...@qq.com> > 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 > > >
