postgres_fdw: Fix connection .

In postgres_fdw, the cached connections to foreign servers will not be
closed until the local session exits if the user mappings or foreign servers
that those connections depend on are dropped. Those connections can be
.

To fix that connection  issue, after a change to a pg_foreign_server
or pg_user_mapping catalog entry, this commit makes postgres_fdw close
the connections depending on that entry immediately if current
transaction has not used those connections yet. Otherwise, mark those
connections as invalid and then close them at the end of current transaction,
since they cannot be closed in the midst of the transaction using them.
Closed connections will be remade at the next opportunity if necessary.

Back- to all supported branches.

Author: Bharath Rupireddy
Reviewed-by: Zhihong Yu, Zhijie Hou, Fujii Masao
Discussion: https://postgr.es/m/CALj2ACVNcGH_6qLY-4_tXz8JLvA+4yeBThRfxMz7Oxbk1aHcpQ@mail.gmail.com

diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c
index 66581e5414401acf6a5d13f80d38a91d89106135..d841cec39b563882378aa192acb17fb7876829f9 100644 (file)
--- a/contrib/postgres_fdw/connection.c
+++ b/contrib/postgres_fdw/connection.c
@@ -940,12 +940,14 @@ pgfdw_xact_callback(XactEvent event, void *arg)
        entry->xact_depth = 0;
 
        /*
-        * If the connection isn't in a good idle state, discard it to
-        * recover. Next GetConnection will open a new connection.
+        * If the connection isn't in a good idle state or it is marked as
+        * invalid, then discard it to recover. Next GetConnection will open a
+        * new connection.
         */
        if (PQstatus(entry->conn) != CONNECTION_OK ||
            PQtransactionStatus(entry->conn) != PQTRANS_IDLE ||
-           entry->changing_xact_state)
+           entry->changing_xact_state ||
+           entry->invalidated)
        {
            elog(DEBUG3, "discarding connection %p", entry->conn);
            disconnect_pg_server(entry);
@@ -1069,9 +1071,12 @@ pgfdw_subxact_callback(SubXactEvent event, SubTransactionId mySubid,
  * Connection invalidation callback function
  *
  * After a change to a pg_foreign_server or pg_user_mapping catalog entry,
- * mark connections depending on that entry as needing to be remade.
- * We can't immediately destroy them, since they might be in the midst of
- * a transaction, but we'll remake them at the next opportunity.
+ * close connections depending on that entry immediately if current transaction
+ * has not used those connections yet. Otherwise, mark those connections as
+ * invalid and then make pgfdw_xact_callback() close them at the end of current
+ * transaction, since they cannot be closed in the midst of the transaction
+ * using them. Closed connections will be remade at the next opportunity if
+ * necessary.
  *
  * Although most cache invalidation callbacks blow away all the related stuff
  * regardless of the given hashvalue, connections are expensive enough that
@@ -1102,7 +1107,21 @@ pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue)
             entry->server_hashvalue == hashvalue) ||
            (cacheid == USERMAPPINGOID &&
             entry->mapping_hashvalue == hashvalue))
-           entry->invalidated = true;
+       {
+           /*
+            * Close the connection immediately if it's not used yet in this
+            * transaction. Otherwise mark it as invalid so that
+            * pgfdw_xact_callback() can close it at the end of this
+            * transaction.
+            */
+           if (entry->xact_depth == 0)
+           {
+               elog(DEBUG3, "discarding connection %p", entry->conn);
+               disconnect_pg_server(entry);
+           }
+           else
+               entry->invalidated = true;
+       }
    }
 }
 

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 2d88d0635837b89dcc1a8427c0247ee50deb6bc9..c11092f8cc59b7e344bca4f0cf7b8c792fc91ae4 100644 (file)
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -9035,3 +9035,21 @@ ERROR:  08006
 COMMIT;
 -- Clean up
 DROP PROCEDURE terminate_backend_and_wait(text);
+-- ===================================================================
+-- test connection invalidation cases
+-- ===================================================================
+-- This test case is for closing the connection in pgfdw_xact_callback
+BEGIN;
+-- Connection xact depth becomes 1 i.e. the connection is in midst of the xact.
+SELECT 1 FROM ft1 LIMIT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+-- Connection is not closed at the end of the alter statement in
+-- pgfdw_inval_callback. That's because the connection is in midst of this
+-- xact, it is just marked as invalid.
+ALTER SERVER loopback OPTIONS (ADD use_remote_estimate 'off');
+-- The invalid connection gets closed in pgfdw_xact_callback during commit.
+COMMIT;

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 7581c5417b90d0dae1604e8ded5e66f2431035f5..25dbc08b988f4d3a7ef5d48547394672fdc1a3f2 100644 (file)
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -2697,3 +2697,17 @@ COMMIT;
 
 -- Clean up
 DROP PROCEDURE terminate_backend_and_wait(text);
+
+-- ===================================================================
+-- test connection invalidation cases
+-- ===================================================================
+-- This test case is for closing the connection in pgfdw_xact_callback
+BEGIN;
+-- Connection xact depth becomes 1 i.e. the connection is in midst of the xact.
+SELECT 1 FROM ft1 LIMIT 1;
+-- Connection is not closed at the end of the alter statement in
+-- pgfdw_inval_callback. That's because the connection is in midst of this
+-- xact, it is just marked as invalid.
+ALTER SERVER loopback OPTIONS (ADD use_remote_estimate 'off');
+-- The invalid connection gets closed in pgfdw_xact_callback during commit.
+COMMIT;