*/
#include "postgres.h"
+#if HAVE_POLL_H
+#include <poll.h>
+#endif
+
#include "access/htup_details.h"
#include "access/xact.h"
#include "catalog/pg_user_mapping.h"
static bool disconnect_cached_connections(Oid serverid);
static void postgres_fdw_get_connections_internal(FunctionCallInfo fcinfo,
enum pgfdwVersion api_version);
+static int pgfdw_conn_check(PGconn *conn);
+static bool pgfdw_conn_checkable(void);
/*
* Get a PGconn which can be used to execute queries on the remote PostgreSQL
/* Number of output arguments (columns) for various API versions */
#define POSTGRES_FDW_GET_CONNECTIONS_COLS_V1_1 2
-#define POSTGRES_FDW_GET_CONNECTIONS_COLS_V1_2 3
-#define POSTGRES_FDW_GET_CONNECTIONS_COLS 3 /* maximum of above */
+#define POSTGRES_FDW_GET_CONNECTIONS_COLS_V1_2 4
+#define POSTGRES_FDW_GET_CONNECTIONS_COLS 4 /* maximum of above */
/*
* Internal function used by postgres_fdw_get_connections variants.
*
- * For API version 1.1, this function returns a set of records with
- * the following values:
+ * For API version 1.1, this function takes no input parameter and
+ * returns a set of records with the following values:
*
* - server_name - server name of active connection. In case the foreign server
* is dropped but still the connection is active, then the server name will
* - valid - true/false representing whether the connection is valid or not.
* Note that connections can become invalid in pgfdw_inval_callback.
*
- * For API version 1.2 and later, this function returns the following
- * additional value along with the two values from version 1.1:
+ * For API version 1.2 and later, this function takes an input parameter
+ * to check a connection status and returns the following
+ * additional values along with the two values from version 1.1:
*
* - used_in_xact - true if the connection is used in the current transaction.
+ * - closed: true if the connection is closed.
*
* No records are returned when there are no cached connections at all.
*/
if (api_version >= PGFDW_V1_2)
{
+ bool check_conn = PG_GETARG_BOOL(0);
+
/* Is this connection used in the current transaction? */
values[2] = BoolGetDatum(entry->xact_depth > 0);
+
+ /*
+ * If a connection status check is requested and supported, return
+ * whether the connection is closed. Otherwise, return NULL.
+ */
+ if (check_conn && pgfdw_conn_checkable())
+ values[3] = BoolGetDatum(pgfdw_conn_check(entry->conn) != 0);
+ else
+ nulls[3] = true;
}
tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
return result;
}
+
+/*
+ * Check if the remote server closed the connection.
+ *
+ * Returns 1 if the connection is closed, -1 if an error occurred,
+ * and 0 if it's not closed or if the connection check is unavailable
+ * on this platform.
+ */
+static int
+pgfdw_conn_check(PGconn *conn)
+{
+ int sock = PQsocket(conn);
+
+ if (PQstatus(conn) != CONNECTION_OK || sock == -1)
+ return -1;
+
+#if (defined(HAVE_POLL) && defined(POLLRDHUP))
+ {
+ struct pollfd input_fd;
+ int result;
+
+ input_fd.fd = sock;
+ input_fd.events = POLLRDHUP;
+ input_fd.revents = 0;
+
+ do
+ result = poll(&input_fd, 1, 0);
+ while (result < 0 && errno == EINTR);
+
+ if (result < 0)
+ return -1;
+
+ return (input_fd.revents & POLLRDHUP) ? 1 : 0;
+ }
+#else
+ return 0;
+#endif
+}
+
+/*
+ * Check if connection status checking is available on this platform.
+ *
+ * Returns true if available, false otherwise.
+ */
+static bool
+pgfdw_conn_checkable(void)
+{
+#if (defined(HAVE_POLL) && defined(POLLRDHUP))
+ return true;
+#else
+ return false;
+#endif
+}
-- should be output as invalid connections. Also the server name for
-- loopback3 should be NULL because the server was dropped.
SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
- server_name | valid | used_in_xact
--------------+-------+--------------
- loopback | f | t
- | f | t
+ server_name | valid | used_in_xact | closed
+-------------+-------+--------------+--------
+ loopback | f | t |
+ | f | t |
(2 rows)
-- The invalid connections get closed in pgfdw_xact_callback during commit.
-- cleanup
DROP FOREIGN TABLE analyze_ftable;
DROP TABLE analyze_table;
+-- ===================================================================
+-- test for postgres_fdw_get_connections function with check_conn = true
+-- ===================================================================
+-- Disable debug_discard_caches in order to manage remote connections
+SET debug_discard_caches TO '0';
+-- The text of the error might vary across platforms, so only show SQLSTATE.
+\set VERBOSITY sqlstate
+SELECT 1 FROM postgres_fdw_disconnect_all();
+ ?column?
+----------
+ 1
+(1 row)
+
+ALTER SERVER loopback OPTIONS (SET application_name 'fdw_conn_check');
+SELECT 1 FROM ft1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+-- Since the remote server is still connected, "closed" should be FALSE,
+-- or NULL if the connection status check is not available.
+SELECT CASE WHEN closed IS NOT true THEN 1 ELSE 0 END
+ FROM postgres_fdw_get_connections(true);
+ case
+------
+ 1
+(1 row)
+
+-- After terminating the remote backend, since the connection is closed,
+-- "closed" should be TRUE, or NULL if the connection status check
+-- is not available.
+DO $$ BEGIN
+PERFORM pg_terminate_backend(pid, 180000) FROM pg_stat_activity
+ WHERE application_name = 'fdw_conn_check';
+END $$;
+SELECT CASE WHEN closed IS NOT false THEN 1 ELSE 0 END
+ FROM postgres_fdw_get_connections(true);
+ case
+------
+ 1
+(1 row)
+
+-- Clean up
+\set VERBOSITY default
+RESET debug_discard_caches;
/* Then we can drop it */
DROP FUNCTION postgres_fdw_get_connections ();
-CREATE FUNCTION postgres_fdw_get_connections (OUT server_name text,
- OUT valid boolean, OUT used_in_xact boolean)
+CREATE FUNCTION postgres_fdw_get_connections (
+ IN check_conn boolean DEFAULT false, OUT server_name text,
+ OUT valid boolean, OUT used_in_xact boolean, OUT closed boolean)
RETURNS SETOF record
AS 'MODULE_PATHNAME', 'postgres_fdw_get_connections_1_2'
LANGUAGE C STRICT PARALLEL RESTRICTED;
-- cleanup
DROP FOREIGN TABLE analyze_ftable;
DROP TABLE analyze_table;
+
+-- ===================================================================
+-- test for postgres_fdw_get_connections function with check_conn = true
+-- ===================================================================
+
+-- Disable debug_discard_caches in order to manage remote connections
+SET debug_discard_caches TO '0';
+
+-- The text of the error might vary across platforms, so only show SQLSTATE.
+\set VERBOSITY sqlstate
+
+SELECT 1 FROM postgres_fdw_disconnect_all();
+ALTER SERVER loopback OPTIONS (SET application_name 'fdw_conn_check');
+SELECT 1 FROM ft1 LIMIT 1;
+
+-- Since the remote server is still connected, "closed" should be FALSE,
+-- or NULL if the connection status check is not available.
+SELECT CASE WHEN closed IS NOT true THEN 1 ELSE 0 END
+ FROM postgres_fdw_get_connections(true);
+
+-- After terminating the remote backend, since the connection is closed,
+-- "closed" should be TRUE, or NULL if the connection status check
+-- is not available.
+DO $$ BEGIN
+PERFORM pg_terminate_backend(pid, 180000) FROM pg_stat_activity
+ WHERE application_name = 'fdw_conn_check';
+END $$;
+SELECT CASE WHEN closed IS NOT false THEN 1 ELSE 0 END
+ FROM postgres_fdw_get_connections(true);
+
+-- Clean up
+\set VERBOSITY default
+RESET debug_discard_caches;
<variablelist>
<varlistentry>
- <term><function>postgres_fdw_get_connections(OUT server_name text,
- OUT valid boolean, OUT used_in_xact boolean)
+ <term><function>postgres_fdw_get_connections(
+ IN check_conn boolean DEFAULT false, OUT server_name text,
+ OUT valid boolean, OUT used_in_xact boolean, OUT closed boolean)
returns setof record</function></term>
<listitem>
<para>
This function returns information about all open connections postgres_fdw
has established from the local session to foreign servers. If there are
no open connections, no records are returned.
+ </para>
+ <para>
+ If <literal>check_conn</literal> is set to <literal>true</literal>,
+ the function checks the status of each connection and shows
+ the result in the <literal>closed</literal> column.
+ This feature is currently available only on systems that support
+ the non-standard <symbol>POLLRDHUP</symbol> extension to
+ the <symbol>poll</symbol> system call, including Linux.
+ This is useful to check if all connections used within
+ a transaction are still open. If any connections are closed,
+ the transaction cannot be committed successfully,
+ so it is better to roll back as soon as a closed connection is detected,
+ rather than continuing to the end. Users can roll back the transaction
+ immediately if the function reports connections where both
+ <literal>used_in_xact</literal> and <literal>closed</literal> are
+ <literal>true</literal>.
+ </para>
+ <para>
Example usage of the function:
<screen>
-postgres=*# SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
- server_name | valid | used_in_xact
--------------+-------+--------------
- loopback1 | t | t
- loopback2 | f | t
+ server_name | valid | used_in_xact | closed
+-------------+-------+--------------+--------
+ loopback1 | t | t |
+ loopback2 | f | t |
</screen>
The output columns are described in
<xref linkend="postgres-fdw-get-connections-columns"/>.
True if this connection is used in the current transaction.
</entry>
</row>
+ <row>
+ <entry><structfield>closed</structfield></entry>
+ <entry><type>boolean</type></entry>
+ <entry>
+ True if this connection is closed, false otherwise.
+ <literal>NULL</literal> is returned if <literal>check_conn</literal>
+ is set to <literal>false</literal> or if the connection status check
+ is not available on this platform.
+ </entry>
+ </row>
</tbody>
</tgroup>
</table>
projects / postgresql.git / commitdiff