On Sat, Jan 16, 2021 at 10:36 AM Bharath Rupireddy
<bharath.rupireddyforpostg...@gmail.com> wrote:
> > > Please consider the v9 patch set for further review.
> >
> > Thanks for updating the patch! I reviewed only 0001 patch.
I addressed the review comments and attached v10 patch set. Please
consider it for further review.
With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com
From 3cf7d7d4d7241460997530ed01c2a53508257786 Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddy@enterprisedb.com>
Date: Sun, 17 Jan 2021 12:30:22 +0530
Subject: [PATCH v10 1/3] postgres_fdw function to discard cached connections
This patch introduces new function postgres_fdw_disconnect() when
called with a foreign server name discards the associated
connections with the server name. When called without any argument,
discards all the existing cached connections.
This patch also adds another function postgres_fdw_get_connections()
to get the list of all cached connections by corresponding foreign
server names.
---
contrib/postgres_fdw/Makefile | 2 +-
contrib/postgres_fdw/connection.c | 330 +++++++++++++-
.../postgres_fdw/expected/postgres_fdw.out | 414 +++++++++++++++++-
.../postgres_fdw/postgres_fdw--1.0--1.1.sql | 20 +
contrib/postgres_fdw/postgres_fdw.control | 2 +-
contrib/postgres_fdw/sql/postgres_fdw.sql | 160 +++++++
doc/src/sgml/postgres-fdw.sgml | 90 ++++
7 files changed, 999 insertions(+), 19 deletions(-)
create mode 100644 contrib/postgres_fdw/postgres_fdw--1.0--1.1.sql
diff --git a/contrib/postgres_fdw/Makefile b/contrib/postgres_fdw/Makefile
index ee8a80a392..c1b0cad453 100644
--- a/contrib/postgres_fdw/Makefile
+++ b/contrib/postgres_fdw/Makefile
@@ -14,7 +14,7 @@ PG_CPPFLAGS = -I$(libpq_srcdir)
SHLIB_LINK_INTERNAL = $(libpq)
EXTENSION = postgres_fdw
-DATA = postgres_fdw--1.0.sql
+DATA = postgres_fdw--1.0.sql postgres_fdw--1.0--1.1.sql
REGRESS = postgres_fdw
diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c
index eaedfea9f2..b6da4899ea 100644
--- a/contrib/postgres_fdw/connection.c
+++ b/contrib/postgres_fdw/connection.c
@@ -16,12 +16,14 @@
#include "access/xact.h"
#include "catalog/pg_user_mapping.h"
#include "commands/defrem.h"
+#include "funcapi.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postgres_fdw.h"
#include "storage/fd.h"
#include "storage/latch.h"
+#include "utils/builtins.h"
#include "utils/datetime.h"
#include "utils/hsearch.h"
#include "utils/inval.h"
@@ -66,6 +68,7 @@ typedef struct ConnCacheEntry
* Connection cache (initialized on first use)
*/
static HTAB *ConnectionHash = NULL;
+static bool conn_cache_destroyed = false;
/* for assigning cursor numbers and prepared statement numbers */
static unsigned int cursor_number = 0;
@@ -74,6 +77,12 @@ static unsigned int prep_stmt_number = 0;
/* tracks whether any work is needed in callback functions */
static bool xact_got_connection = false;
+/*
+ * SQL functions
+ */
+PG_FUNCTION_INFO_V1(postgres_fdw_get_connections);
+PG_FUNCTION_INFO_V1(postgres_fdw_disconnect);
+
/* prototypes of private functions */
static void make_new_connection(ConnCacheEntry *entry, UserMapping *user);
static PGconn *connect_pg_server(ForeignServer *server, UserMapping *user);
@@ -95,6 +104,8 @@ static bool pgfdw_exec_cleanup_query(PGconn *conn, const char *query,
static bool pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime,
PGresult **result);
static bool UserMappingPasswordRequired(UserMapping *user);
+static bool disconnect_cached_connections(uint32 hashvalue, bool all,
+ bool *is_in_use);
/*
* Get a PGconn which can be used to execute queries on the remote PostgreSQL
@@ -127,15 +138,20 @@ GetConnection(UserMapping *user, bool will_prep_stmt)
HASH_ELEM | HASH_BLOBS);
/*
- * Register some callback functions that manage connection cleanup.
- * This should be done just once in each backend.
+ * Register callback functions that manage connection cleanup. This
+ * should be done just once in each backend. We don't register the
+ * callbacks again, if the connection cache is destroyed at least once
+ * in the backend.
*/
- RegisterXactCallback(pgfdw_xact_callback, NULL);
- RegisterSubXactCallback(pgfdw_subxact_callback, NULL);
- CacheRegisterSyscacheCallback(FOREIGNSERVEROID,
- pgfdw_inval_callback, (Datum) 0);
- CacheRegisterSyscacheCallback(USERMAPPINGOID,
- pgfdw_inval_callback, (Datum) 0);
+ if (!conn_cache_destroyed)
+ {
+ RegisterXactCallback(pgfdw_xact_callback, NULL);
+ RegisterSubXactCallback(pgfdw_subxact_callback, NULL);
+ CacheRegisterSyscacheCallback(FOREIGNSERVEROID,
+ pgfdw_inval_callback, (Datum) 0);
+ CacheRegisterSyscacheCallback(USERMAPPINGOID,
+ pgfdw_inval_callback, (Datum) 0);
+ }
}
/* Set flag that we did GetConnection during the current transaction */
@@ -1095,6 +1111,13 @@ pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue)
Assert(cacheid == FOREIGNSERVEROID || cacheid == USERMAPPINGOID);
+ /*
+ * Quick exit if the cache has been destroyed in
+ * disconnect_cached_connections.
+ */
+ if (!ConnectionHash)
+ return;
+
/* ConnectionHash must exist already, if we're registered */
hash_seq_init(&scan, ConnectionHash);
while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
@@ -1335,3 +1358,294 @@ exit: ;
*result = last_res;
return timed_out;
}
+
+/*
+ * List active foreign server connections.
+ *
+ * This function takes no input parameter and returns setof record made of
+ * 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
+ * be NULL in output.
+ * - valid - true/false representing whether the connection is valid or not.
+ * Note that the connections can get invalidated in pgfdw_inval_callback.
+ *
+ * No records are returned when there are no cached connections at all.
+ */
+Datum
+postgres_fdw_get_connections(PG_FUNCTION_ARGS)
+{
+ ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+ TupleDesc tupdesc;
+ Tuplestorestate *tupstore;
+ MemoryContext per_query_ctx;
+ MemoryContext oldcontext;
+ HASH_SEQ_STATUS scan;
+ ConnCacheEntry *entry;
+
+ /* check to see if caller supports us returning a tuplestore */
+ if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("set-valued function called in context that cannot accept a set")));
+ if (!(rsinfo->allowedModes & SFRM_Materialize))
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("materialize mode required, but it is not allowed in this context")));
+
+ /* Build a tuple descriptor for our result type */
+ if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+ elog(ERROR, "return type must be a row type");
+
+ /* Build tuplestore to hold the result rows */
+ per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
+ oldcontext = MemoryContextSwitchTo(per_query_ctx);
+
+ tupstore = tuplestore_begin_heap(true, false, work_mem);
+ rsinfo->returnMode = SFRM_Materialize;
+ rsinfo->setResult = tupstore;
+ rsinfo->setDesc = tupdesc;
+
+ MemoryContextSwitchTo(oldcontext);
+
+ /* If cache doesn't exist, we return no records. */
+ if (!ConnectionHash)
+ {
+ /* clean up and return the tuplestore */
+ tuplestore_donestoring(tupstore);
+
+ PG_RETURN_VOID();
+ }
+
+ hash_seq_init(&scan, ConnectionHash);
+ while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
+ {
+ ForeignServer *server;
+ bits16 flags = FSV_MISSING_OK;
+ Datum values[2];
+ bool nulls[2];
+
+ /* We only look for open remote connections. */
+ if (!entry->conn)
+ continue;
+
+ server = GetForeignServerExtended(entry->serverid, flags);
+
+ /*
+ * The foreign server may have been dropped in current explicit
+ * transaction. It is not possible to drop the server from another
+ * session when the connection associated with it is in use in the
+ * current transaction, if tried so, the drop query in another session
+ * blocks until the current transaction finishes.
+ *
+ * Even though the server is dropped in the current transaction, the
+ * cache can still have associated active connection entry, say we call
+ * such connections dangling. Since we can not fetch the server name
+ * from system catalogues for dangling connections, instead we show
+ * NULL value for server name in output.
+ *
+ * We could have done better by storing the server name in the cache
+ * entry instead of server oid so that it could be used in the output.
+ * But the server name in each cache entry requires 64 bytes of memory,
+ * which is huge, when there are many cached connections and the use
+ * case i.e. dropping the foreign server within the explicit current
+ * transaction seems rare. So, we chose to show NULL value for server
+ * name in output.
+ *
+ * Such dangling connections get closed either in next use or at the
+ * end of current explicit transaction in pgfdw_xact_callback.
+ */
+ if (!server)
+ {
+ /*
+ * If the server has been dropped in the current explicit
+ * transaction, then this entry would have been invalidated in
+ * pgfdw_inval_callback at the end of drop sever command. Note that
+ * this connection would not have been closed in
+ * pgfdw_inval_callback because it is still being used in the
+ * current explicit transaction. So, assert that here.
+ */
+ Assert(entry->conn && entry->xact_depth > 0 && entry->invalidated);
+
+ /* Show null, if no server name was found. */
+ values[0] = (Datum) NULL;
+ nulls[0] = true;
+ }
+ else
+ {
+ values[0] = CStringGetTextDatum(server->servername);
+ nulls[0] = false;
+ }
+
+ values[1] = BoolGetDatum(!entry->invalidated);
+ nulls[1] = false;
+
+ tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+ }
+
+ /* clean up and return the tuplestore */
+ tuplestore_donestoring(tupstore);
+
+ PG_RETURN_VOID();
+}
+
+/*
+ * Disconnect cached connections.
+ *
+ * If server name is provided as input, this function disconnects the
+ * associated cached connection. Otherwise all the cached connections are
+ * disconnected. The cache can be destroyed when there are no active
+ * connections left.
+ *
+ * This function returns false if the cache doesn't exist.
+ * When the cache exists:
+ * 1) If the server name is provided, it first checks whether the foreign
+ * server exists, if not, an error is emitted. Otherwise it disconnects the
+ * associated connection when it's not being used in current transaction
+ * and returns true. If it's in use, then issues a warning and returns
+ * false.
+ * 2) If no input argument is provided, then it tries to disconnect all the
+ * connections. If all the connections are not being used, then it
+ * disconnects them and returns true. If all the connections are being
+ * used, then it issues a warning and returns false. If at least one
+ * connection is closed and others are in use, then issues a warning and
+ * returns true.
+ */
+Datum
+postgres_fdw_disconnect(PG_FUNCTION_ARGS)
+{
+ bool result = false;
+ bool is_in_use = false;
+
+ if (!ConnectionHash)
+ PG_RETURN_BOOL(result);
+
+ if (PG_NARGS() == 1)
+ {
+ ForeignServer *server = NULL;
+ char *servername = NULL;
+ uint32 hashvalue;
+
+ servername = text_to_cstring(PG_GETARG_TEXT_PP(0));
+ server = GetForeignServerByName(servername, true);
+
+ if (!server)
+ ereport(ERROR,
+ (errcode(ERRCODE_CONNECTION_DOES_NOT_EXIST),
+ errmsg("foreign server \"%s\" does not exist", servername)));
+
+ hashvalue = GetSysCacheHashValue1(FOREIGNSERVEROID,
+ ObjectIdGetDatum(server->serverid));
+ result = disconnect_cached_connections(hashvalue, false, &is_in_use);
+
+ /*
+ * Check if the connection associated with the given foreign server is
+ * in use i.e. entry->xact_depth > 0. Since we can not close it, so
+ * error out.
+ */
+ if (is_in_use)
+ ereport(WARNING,
+ (errmsg("cannot close the connection because it is still in use")));
+ }
+ else
+ {
+ result = disconnect_cached_connections(0, true, &is_in_use);
+
+ /*
+ * Check if some or all of the connections are in use i.e.
+ * entry->xact_depth > 0. Since we can not close them, so inform the
+ * user.
+ */
+ if (is_in_use)
+ {
+ if (result)
+ {
+ /* We closed at least one connection. Others are in use. */
+ ereport(WARNING,
+ (errmsg("cannot close all connections because some of them are still in use")));
+ }
+ else
+ {
+ /* We did not closed any connection, all are in use. */
+ ereport(WARNING,
+ (errmsg("cannot close any connection because they are still in use")));
+ }
+ }
+ }
+
+ PG_RETURN_BOOL(result);
+}
+
+/*
+ * Workhorse to disconnect the cached connections.
+ *
+ * This function tries to disconnect the connections only when they are not in
+ * use in the current transaction.
+ *
+ * If all is true, all the cached connections that are not being used in the
+ * current transaction are disconnected. Otherwise, the unused entries with the
+ * given hashvalue are disconnected.
+ *
+ * This function destroys the cache when there are no active connections. And
+ * set is_in_use flag to true when there exists at least one connection that's
+ * being used in the current transaction.
+ *
+ * This function returns true in the following cases if at least one connection
+ * is disconnected. Otherwise it returns false.
+ */
+static bool
+disconnect_cached_connections(uint32 hashvalue, bool all, bool *is_in_use)
+{
+ HASH_SEQ_STATUS scan;
+ ConnCacheEntry *entry;
+ bool result = false;
+ bool active_conn_exists = false;
+
+ /* We are here only when ConnectionHash exists. */
+ Assert(ConnectionHash);
+
+ hash_seq_init(&scan, ConnectionHash);
+ while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
+ {
+ /*
+ * Either disconnect given or all the active and not in use cached
+ * connections.
+ */
+ if ((all || entry->server_hashvalue == hashvalue) &&
+ entry->conn)
+ {
+ if (entry->xact_depth > 0)
+ *is_in_use = true;
+ else
+ {
+ elog(DEBUG3, "discarding connection %p", entry->conn);
+ disconnect_pg_server(entry);
+ result = true;
+ }
+ }
+
+ /*
+ * If at least one active connection exists in the cache, mark it so
+ * that we don't destroy the cache.
+ */
+ if (entry->conn && !active_conn_exists)
+ active_conn_exists = true;
+ }
+
+ /*
+ * Destroy the cache if we discarded all active connections i.e. if there
+ * is no single active connection, which we can know while scanning the
+ * cached entries in the above loop. Destroying the cache is better than to
+ * keep it in the memory with all inactive entries in it to save some
+ * memory. Cache can get initialized on the subsequent queries to foreign
+ * server.
+ */
+ if (!active_conn_exists)
+ {
+ hash_destroy(ConnectionHash);
+ ConnectionHash = NULL;
+ conn_cache_destroyed = true;
+ }
+
+ return result;
+}
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index c11092f8cc..4a0078b1e7 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -13,12 +13,22 @@ DO $d$
OPTIONS (dbname '$$||current_database()||$$',
port '$$||current_setting('port')||$$'
)$$;
+ EXECUTE $$CREATE SERVER temploopback1 FOREIGN DATA WRAPPER postgres_fdw
+ OPTIONS (dbname '$$||current_database()||$$',
+ port '$$||current_setting('port')||$$'
+ )$$;
+ EXECUTE $$CREATE SERVER temploopback2 FOREIGN DATA WRAPPER postgres_fdw
+ OPTIONS (dbname '$$||current_database()||$$',
+ port '$$||current_setting('port')||$$'
+ )$$;
END;
$d$;
CREATE USER MAPPING FOR public SERVER testserver1
OPTIONS (user 'value', password 'value');
CREATE USER MAPPING FOR CURRENT_USER SERVER loopback;
CREATE USER MAPPING FOR CURRENT_USER SERVER loopback2;
+CREATE USER MAPPING FOR public SERVER temploopback1;
+CREATE USER MAPPING FOR public SERVER temploopback2;
-- ===================================================================
-- create objects used through FDW loopback server
-- ===================================================================
@@ -129,6 +139,16 @@ CREATE FOREIGN TABLE ft6 (
c2 int NOT NULL,
c3 text
) SERVER loopback2 OPTIONS (schema_name 'S 1', table_name 'T 4');
+CREATE FOREIGN TABLE templbtbl1 (
+ c1 int NOT NULL,
+ c2 int NOT NULL,
+ c3 text
+) SERVER temploopback1 OPTIONS (schema_name 'S 1', table_name 'T 4');
+CREATE FOREIGN TABLE templbtbl2 (
+ c1 int NOT NULL,
+ c2 int NOT NULL,
+ c3 text
+) SERVER temploopback2 OPTIONS (schema_name 'S 1', table_name 'T 4');
-- ===================================================================
-- tests for validator
-- ===================================================================
@@ -191,15 +211,17 @@ ALTER FOREIGN TABLE ft2 OPTIONS (schema_name 'S 1', table_name 'T 1');
ALTER FOREIGN TABLE ft1 ALTER COLUMN c1 OPTIONS (column_name 'C 1');
ALTER FOREIGN TABLE ft2 ALTER COLUMN c1 OPTIONS (column_name 'C 1');
\det+
- List of foreign tables
- Schema | Table | Server | FDW options | Description
---------+-------+-----------+---------------------------------------+-------------
- public | ft1 | loopback | (schema_name 'S 1', table_name 'T 1') |
- public | ft2 | loopback | (schema_name 'S 1', table_name 'T 1') |
- public | ft4 | loopback | (schema_name 'S 1', table_name 'T 3') |
- public | ft5 | loopback | (schema_name 'S 1', table_name 'T 4') |
- public | ft6 | loopback2 | (schema_name 'S 1', table_name 'T 4') |
-(5 rows)
+ List of foreign tables
+ Schema | Table | Server | FDW options | Description
+--------+------------+---------------+---------------------------------------+-------------
+ public | ft1 | loopback | (schema_name 'S 1', table_name 'T 1') |
+ public | ft2 | loopback | (schema_name 'S 1', table_name 'T 1') |
+ public | ft4 | loopback | (schema_name 'S 1', table_name 'T 3') |
+ public | ft5 | loopback | (schema_name 'S 1', table_name 'T 4') |
+ public | ft6 | loopback2 | (schema_name 'S 1', table_name 'T 4') |
+ public | templbtbl1 | temploopback1 | (schema_name 'S 1', table_name 'T 4') |
+ public | templbtbl2 | temploopback2 | (schema_name 'S 1', table_name 'T 4') |
+(7 rows)
-- Test that alteration of server options causes reconnection
-- Remote's errors might be non-English, so hide them to ensure stable results
@@ -9053,3 +9075,377 @@ SELECT 1 FROM ft1 LIMIT 1;
ALTER SERVER loopback OPTIONS (ADD use_remote_estimate 'off');
-- The invalid connection gets closed in pgfdw_xact_callback during commit.
COMMIT;
+-- ========================================================================
+-- Test postgres_fdw_get_connections and postgres_fdw_disconnect functions
+-- ========================================================================
+-- Discard all existing connections, before starting the tests.
+SELECT postgres_fdw_disconnect(); /* TRUE */
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
+-- Ensure to have temploopback1 and temploopback2 connections cached.
+SELECT 1 FROM templbtbl1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+SELECT 1 FROM templbtbl2 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+-- List all the existing cached connections. Should output temploopback1,
+-- temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback1 | t
+ temploopback2 | t
+(2 rows)
+
+-- temploopback1 connection is disconnected. temploopback2 connection still
+-- exists.
+SELECT postgres_fdw_disconnect('temploopback1'); /* TRUE */
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
+-- List all the existing cached connections. Should output temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback2 | t
+(1 row)
+
+-- Cache exists, but the temploopback1 connection is not present in it.
+SELECT postgres_fdw_disconnect('temploopback1'); /* FALSE */
+ postgres_fdw_disconnect
+-------------------------
+ f
+(1 row)
+
+-- Cache exists, but the server name provided doesn't exist.
+SELECT postgres_fdw_disconnect('unknownserver'); /* ERROR */
+ERROR: foreign server "unknownserver" does not exist
+-- Cache and temploopback2 connection exist, so discard it.
+SELECT postgres_fdw_disconnect(); /* TRUE */
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
+-- Cache does not exist.
+SELECT postgres_fdw_disconnect(); /* FALSE */
+ postgres_fdw_disconnect
+-------------------------
+ f
+(1 row)
+
+-- Test the functions inside explicit xact.
+-- Connections are being used in the xact, so they cannot be disconnected.
+BEGIN;
+SELECT 1 FROM templbtbl1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+SELECT 1 FROM templbtbl2 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback1 | t
+ temploopback2 | t
+(2 rows)
+
+SELECT * FROM postgres_fdw_disconnect('temploopback1'); /* WARNING and FALSE */
+WARNING: cannot close the connection because it is still in use
+ postgres_fdw_disconnect
+-------------------------
+ f
+(1 row)
+
+SELECT * FROM postgres_fdw_disconnect(); /* WARNING and FALSE */
+WARNING: cannot close any connection because they are still in use
+ postgres_fdw_disconnect
+-------------------------
+ f
+(1 row)
+
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback1 | t
+ temploopback2 | t
+(2 rows)
+
+COMMIT;
+-- Should disconnect temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
+-- Connections can be closed in the xact because they are not in use.
+SELECT 1 FROM templbtbl1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+SELECT 1 FROM templbtbl2 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+BEGIN;
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback1 | t
+ temploopback2 | t
+(2 rows)
+
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
+-- Should output nothing.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+-------------+-------
+(0 rows)
+
+COMMIT;
+-- temploopback1 connection is closed and temploopback2 is not, because it's
+-- being used in the xact.
+SELECT 1 FROM templbtbl1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+BEGIN;
+SELECT 1 FROM templbtbl2 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback1 | t
+ temploopback2 | t
+(2 rows)
+
+SELECT * FROM postgres_fdw_disconnect('temploopback1'); /* TRUE */
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
+-- Should output temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback2 | t
+(1 row)
+
+COMMIT;
+-- Should disconnect temploopback2.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
+-- temploopback1 connection is closed and temploopback2 is not, because it's
+-- being used in the xact.
+SELECT 1 FROM templbtbl1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+BEGIN;
+SELECT 1 FROM templbtbl2 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback1 | t
+ temploopback2 | t
+(2 rows)
+
+SELECT * FROM postgres_fdw_disconnect(); /* WARNING and TRUE */
+WARNING: cannot close all connections because some of them are still in use
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
+-- Should output temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback2 | t
+(1 row)
+
+COMMIT;
+-- Should disconnect temploopback2.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
+-- temploopback1 connection is invalidated and temploopback2 is not.
+BEGIN;
+SELECT 1 FROM templbtbl1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+SELECT 1 FROM templbtbl2 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+ALTER SERVER temploopback1 OPTIONS (ADD use_remote_estimate 'off');
+-- Should output temploopback1 as invalid, temploopback2 as valid.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback1 | f
+ temploopback2 | t
+(2 rows)
+
+COMMIT;
+-- Invalidated connection i.e. temploopback1 was closed at the end of the xact.
+-- Should output temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback2 | t
+(1 row)
+
+-- Should disconnect temploopback2.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
+-- Both temploopback1 and temploopback2 connections are invalidated.
+BEGIN;
+SELECT 1 FROM templbtbl1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+SELECT 1 FROM templbtbl2 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+ALTER SERVER temploopback1 OPTIONS (SET use_remote_estimate 'off');
+ALTER SERVER temploopback2 OPTIONS (ADD use_remote_estimate 'off');
+-- Should output both temploopback1 and temploopback2 as invalid.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback1 | f
+ temploopback2 | f
+(2 rows)
+
+COMMIT;
+-- Invalidated connections i.e. temploopback1 and temploopback2 were closed at
+-- the end of the xact. Should output nothing.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+-------------+-------
+(0 rows)
+
+-- No active connections.
+SELECT * FROM postgres_fdw_disconnect(); /* FALSE */
+ postgres_fdw_disconnect
+-------------------------
+ f
+(1 row)
+
+-- Both the servers were dropped inside the xact block, so a warning is
+-- emitted.
+BEGIN;
+SELECT 1 FROM templbtbl1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+SELECT 1 FROM templbtbl2 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback1 | t
+ temploopback2 | t
+(2 rows)
+
+DROP SERVER temploopback1 CASCADE;
+NOTICE: drop cascades to 2 other objects
+DETAIL: drop cascades to user mapping for public on server temploopback1
+drop cascades to foreign table templbtbl1
+-- Should output temploopback2 and null server name with valid false.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+---------------+-------
+ temploopback2 | t
+ | f
+(2 rows)
+
+DROP SERVER temploopback2 CASCADE;
+NOTICE: drop cascades to 2 other objects
+DETAIL: drop cascades to user mapping for public on server temploopback2
+drop cascades to foreign table templbtbl2
+-- Should output 2 rows of each null server name with valid false.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+-------------+-------
+ | f
+ | f
+(2 rows)
+
+COMMIT;
diff --git a/contrib/postgres_fdw/postgres_fdw--1.0--1.1.sql b/contrib/postgres_fdw/postgres_fdw--1.0--1.1.sql
new file mode 100644
index 0000000000..b616316999
--- /dev/null
+++ b/contrib/postgres_fdw/postgres_fdw--1.0--1.1.sql
@@ -0,0 +1,20 @@
+/* contrib/postgres_fdw/postgres_fdw--1.0--1.1.sql */
+
+-- complain if script is sourced in psql, rather than via ALTER EXTENSION
+\echo Use "ALTER EXTENSION postgres_fdw UPDATE TO '1.1'" to load this file. \quit
+
+CREATE FUNCTION postgres_fdw_get_connections (OUT server_name text,
+ OUT valid boolean)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME','postgres_fdw_get_connections'
+LANGUAGE C STRICT PARALLEL RESTRICTED;
+
+CREATE FUNCTION postgres_fdw_disconnect ()
+RETURNS bool
+AS 'MODULE_PATHNAME','postgres_fdw_disconnect'
+LANGUAGE C STRICT PARALLEL RESTRICTED;
+
+CREATE FUNCTION postgres_fdw_disconnect (text)
+RETURNS bool
+AS 'MODULE_PATHNAME','postgres_fdw_disconnect'
+LANGUAGE C STRICT PARALLEL RESTRICTED;
diff --git a/contrib/postgres_fdw/postgres_fdw.control b/contrib/postgres_fdw/postgres_fdw.control
index f9ed490752..d489382064 100644
--- a/contrib/postgres_fdw/postgres_fdw.control
+++ b/contrib/postgres_fdw/postgres_fdw.control
@@ -1,5 +1,5 @@
# postgres_fdw extension
comment = 'foreign-data wrapper for remote PostgreSQL servers'
-default_version = '1.0'
+default_version = '1.1'
module_pathname = '$libdir/postgres_fdw'
relocatable = true
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 25dbc08b98..3465cc0f56 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -15,6 +15,14 @@ DO $d$
OPTIONS (dbname '$$||current_database()||$$',
port '$$||current_setting('port')||$$'
)$$;
+ EXECUTE $$CREATE SERVER temploopback1 FOREIGN DATA WRAPPER postgres_fdw
+ OPTIONS (dbname '$$||current_database()||$$',
+ port '$$||current_setting('port')||$$'
+ )$$;
+ EXECUTE $$CREATE SERVER temploopback2 FOREIGN DATA WRAPPER postgres_fdw
+ OPTIONS (dbname '$$||current_database()||$$',
+ port '$$||current_setting('port')||$$'
+ )$$;
END;
$d$;
@@ -22,6 +30,8 @@ CREATE USER MAPPING FOR public SERVER testserver1
OPTIONS (user 'value', password 'value');
CREATE USER MAPPING FOR CURRENT_USER SERVER loopback;
CREATE USER MAPPING FOR CURRENT_USER SERVER loopback2;
+CREATE USER MAPPING FOR public SERVER temploopback1;
+CREATE USER MAPPING FOR public SERVER temploopback2;
-- ===================================================================
-- create objects used through FDW loopback server
@@ -142,6 +152,17 @@ CREATE FOREIGN TABLE ft6 (
c3 text
) SERVER loopback2 OPTIONS (schema_name 'S 1', table_name 'T 4');
+CREATE FOREIGN TABLE templbtbl1 (
+ c1 int NOT NULL,
+ c2 int NOT NULL,
+ c3 text
+) SERVER temploopback1 OPTIONS (schema_name 'S 1', table_name 'T 4');
+
+CREATE FOREIGN TABLE templbtbl2 (
+ c1 int NOT NULL,
+ c2 int NOT NULL,
+ c3 text
+) SERVER temploopback2 OPTIONS (schema_name 'S 1', table_name 'T 4');
-- ===================================================================
-- tests for validator
-- ===================================================================
@@ -2711,3 +2732,142 @@ SELECT 1 FROM ft1 LIMIT 1;
ALTER SERVER loopback OPTIONS (ADD use_remote_estimate 'off');
-- The invalid connection gets closed in pgfdw_xact_callback during commit.
COMMIT;
+
+-- ========================================================================
+-- Test postgres_fdw_get_connections and postgres_fdw_disconnect functions
+-- ========================================================================
+
+-- Discard all existing connections, before starting the tests.
+SELECT postgres_fdw_disconnect(); /* TRUE */
+
+-- Ensure to have temploopback1 and temploopback2 connections cached.
+SELECT 1 FROM templbtbl1 LIMIT 1;
+SELECT 1 FROM templbtbl2 LIMIT 1;
+
+-- List all the existing cached connections. Should output temploopback1,
+-- temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+
+-- temploopback1 connection is disconnected. temploopback2 connection still
+-- exists.
+SELECT postgres_fdw_disconnect('temploopback1'); /* TRUE */
+
+-- List all the existing cached connections. Should output temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+
+-- Cache exists, but the temploopback1 connection is not present in it.
+SELECT postgres_fdw_disconnect('temploopback1'); /* FALSE */
+
+-- Cache exists, but the server name provided doesn't exist.
+SELECT postgres_fdw_disconnect('unknownserver'); /* ERROR */
+
+-- Cache and temploopback2 connection exist, so discard it.
+SELECT postgres_fdw_disconnect(); /* TRUE */
+
+-- Cache does not exist.
+SELECT postgres_fdw_disconnect(); /* FALSE */
+
+-- Test the functions inside explicit xact.
+-- Connections are being used in the xact, so they cannot be disconnected.
+BEGIN;
+SELECT 1 FROM templbtbl1 LIMIT 1;
+SELECT 1 FROM templbtbl2 LIMIT 1;
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+SELECT * FROM postgres_fdw_disconnect('temploopback1'); /* WARNING and FALSE */
+SELECT * FROM postgres_fdw_disconnect(); /* WARNING and FALSE */
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+COMMIT;
+
+-- Should disconnect temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+
+-- Connections can be closed in the xact because they are not in use.
+SELECT 1 FROM templbtbl1 LIMIT 1;
+SELECT 1 FROM templbtbl2 LIMIT 1;
+BEGIN;
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+-- Should output nothing.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+COMMIT;
+
+-- temploopback1 connection is closed and temploopback2 is not, because it's
+-- being used in the xact.
+SELECT 1 FROM templbtbl1 LIMIT 1;
+BEGIN;
+SELECT 1 FROM templbtbl2 LIMIT 1;
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+SELECT * FROM postgres_fdw_disconnect('temploopback1'); /* TRUE */
+-- Should output temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+COMMIT;
+
+-- Should disconnect temploopback2.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+
+-- temploopback1 connection is closed and temploopback2 is not, because it's
+-- being used in the xact.
+SELECT 1 FROM templbtbl1 LIMIT 1;
+BEGIN;
+SELECT 1 FROM templbtbl2 LIMIT 1;
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+SELECT * FROM postgres_fdw_disconnect(); /* WARNING and TRUE */
+-- Should output temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+COMMIT;
+
+-- Should disconnect temploopback2.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+
+-- temploopback1 connection is invalidated and temploopback2 is not.
+BEGIN;
+SELECT 1 FROM templbtbl1 LIMIT 1;
+SELECT 1 FROM templbtbl2 LIMIT 1;
+ALTER SERVER temploopback1 OPTIONS (ADD use_remote_estimate 'off');
+-- Should output temploopback1 as invalid, temploopback2 as valid.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+COMMIT;
+
+-- Invalidated connection i.e. temploopback1 was closed at the end of the xact.
+-- Should output temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+
+-- Should disconnect temploopback2.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+
+-- Both temploopback1 and temploopback2 connections are invalidated.
+BEGIN;
+SELECT 1 FROM templbtbl1 LIMIT 1;
+SELECT 1 FROM templbtbl2 LIMIT 1;
+ALTER SERVER temploopback1 OPTIONS (SET use_remote_estimate 'off');
+ALTER SERVER temploopback2 OPTIONS (ADD use_remote_estimate 'off');
+-- Should output both temploopback1 and temploopback2 as invalid.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+COMMIT;
+
+-- Invalidated connections i.e. temploopback1 and temploopback2 were closed at
+-- the end of the xact. Should output nothing.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+
+-- No active connections.
+SELECT * FROM postgres_fdw_disconnect(); /* FALSE */
+
+-- Both the servers were dropped inside the xact block, so a warning is
+-- emitted.
+BEGIN;
+SELECT 1 FROM templbtbl1 LIMIT 1;
+SELECT 1 FROM templbtbl2 LIMIT 1;
+-- Should output temploopback1, temploopback2.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+DROP SERVER temploopback1 CASCADE;
+-- Should output temploopback2 and null server name with valid false.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+DROP SERVER temploopback2 CASCADE;
+-- Should output 2 rows of each null server name with valid false.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+COMMIT;
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml
index e6fd2143c1..1da9599f59 100644
--- a/doc/src/sgml/postgres-fdw.sgml
+++ b/doc/src/sgml/postgres-fdw.sgml
@@ -479,6 +479,82 @@ OPTIONS (ADD password_required 'false');
</sect3>
</sect2>
+<sect2>
+ <title>Functions</title>
+
+ <variablelist>
+ <varlistentry>
+ <term><function>postgres_fdw_get_connections(OUT server_name text, OUT valid boolean) returns setof record</function></term>
+ <listitem>
+ <para>
+ When called in the local session, it returns set of records made of the
+ foreign server names of all the open connections that are previously made
+ to the foreign servers and <literal>true</literal> or <literal>false</literal>
+ to show whether or not the connection is valid. The foreign server
+ connections can get invalidated due to alter statements on foreign server
+ or user mapping such connections get closed at the end of transaction. If
+ there are no open connections, then no record is returned. This function
+ issues a warning in case for any connection, the associated foreign
+ server has been dropped and the server name can not be fetched from the
+ system catalogues. Example usage of the function:
+ <screen>
+postgres=# SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+-------------+-------
+ loopback1 | t
+ loopback2 | f
+</screen>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><function>postgres_fdw_disconnect(IN servername text) returns boolean</function></term>
+ <listitem>
+ <para>
+ When called in the local session with the foreign server name as input,
+ it discards the unused open connection previously made to the foreign
+ server and returns <literal>true</literal>. If the open connection is
+ still being used in the current transaction, it is not discarded, instead
+ a warning is issued and <literal>false</literal> is returned. <literal>false</literal>
+ is returned when there are no open connections. When there are some open
+ connections, but there is no connection for the given foreign server,
+ then <literal>false</literal> is returned. When no foreign server exists
+ with the given name, an error is emitted. Example usage of the function:
+ <screen>
+postgres=# SELECT * FROM postgres_fdw_disconnect('loopback1');
+ postgres_fdw_disconnect
+-------------------------
+ t
+</screen>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><function>postgres_fdw_disconnect() returns boolean</function></term>
+ <listitem>
+ <para>
+ When called in the local session with no input argument, it discards all
+ the unused open connections that are previously made to the foreign
+ servers and returns <literal>true</literal>. If there is any open
+ connection that is still being used in the current transaction, then a
+ warning is issued. <literal>false</literal> is returned when no open
+ connection is discarded or there are no open connections at all. Example
+ usage of the function:
+ <screen>
+postgres=# SELECT * FROM postgres_fdw_disconnect();
+ postgres_fdw_disconnect
+-------------------------
+ t
+</screen>
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+</sect2>
+
<sect2>
<title>Connection Management</title>
@@ -490,6 +566,20 @@ OPTIONS (ADD password_required 'false');
multiple user identities (user mappings) are used to access the foreign
server, a connection is established for each user mapping.
</para>
+
+ <para>
+ Since the <filename>postgres_fdw</filename> keeps the connections to remote
+ servers in the local session, the corresponding sessions that are opened on
+ the remote servers are kept idle until they are re-used by the local session.
+ This may waste resources if those connections are not frequently used by the
+ local session. To address this, the <filename>postgres_fdw</filename>
+ provides following way to remove the connections to the remote servers and
+ so the remote sessions:
+
+ <function>postgres_fdw_disconnect()</function> to discard all the
+ connections or <function>postgres_fdw_disconnect(text)</function>
+ to discard the connection associated with the given foreign server.
+ </para>
</sect2>
<sect2>
--
2.25.1
From ddaaa288e7115457d32420bd177435a98790514f Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddy@enterprisedb.com>
Date: Sat, 16 Jan 2021 11:13:58 +0530
Subject: [PATCH v10 2/3] postgres_fdw add keep_connections GUC to not cache
connections
This patch adds a new GUC postgres_fdw.keep_connections, default
being on, when set to off no remote connections are cached by the
local session.
---
contrib/postgres_fdw/connection.c | 12 +++--
.../postgres_fdw/expected/postgres_fdw.out | 50 +++++++++++++++++++
contrib/postgres_fdw/postgres_fdw.c | 16 ++++++
contrib/postgres_fdw/postgres_fdw.h | 3 ++
contrib/postgres_fdw/sql/postgres_fdw.sql | 30 +++++++++++
doc/src/sgml/postgres-fdw.sgml | 44 +++++++++++++++-
6 files changed, 151 insertions(+), 4 deletions(-)
diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c
index 396ae63415..260e956195 100644
--- a/contrib/postgres_fdw/connection.c
+++ b/contrib/postgres_fdw/connection.c
@@ -815,6 +815,7 @@ pgfdw_xact_callback(XactEvent event, void *arg)
while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
{
PGresult *res;
+ bool used_in_current_xact = false;
/* Ignore cache entry if no open connection right now */
if (entry->conn == NULL)
@@ -825,6 +826,8 @@ pgfdw_xact_callback(XactEvent event, void *arg)
{
bool abort_cleanup_failure = false;
+ used_in_current_xact = true;
+
elog(DEBUG3, "closing remote transaction on connection %p",
entry->conn);
@@ -959,16 +962,19 @@ pgfdw_xact_callback(XactEvent event, void *arg)
/*
* 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.
+ * invalid or keep_connections GUC is false and this connection is used
+ * in current xact, 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->invalidated)
+ entry->invalidated ||
+ (used_in_current_xact && !keep_connections))
{
elog(DEBUG3, "discarding connection %p", entry->conn);
disconnect_pg_server(entry);
+ used_in_current_xact = false;
}
}
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 4a0078b1e7..a655c7025f 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -9449,3 +9449,53 @@ SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
(2 rows)
COMMIT;
+-- ===================================================================
+-- Test postgres_fdw.keep_connections GUC
+-- ===================================================================
+-- By default, keep_connections GUC is on i.e. local session caches all the
+-- foreign server connections.
+SHOW postgres_fdw.keep_connections;
+ postgres_fdw.keep_connections
+-------------------------------
+ on
+(1 row)
+
+-- Set it off i.e. the cached connections which are used after this setting are
+-- disconnected at the end of respective xacts.
+SET postgres_fdw.keep_connections TO off;
+-- Make connection using loopback server, connection should not be cached as
+-- the GUC is off.
+SELECT 1 FROM ft1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+-- Should output nothing.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+-------------+-------
+(0 rows)
+
+-- Set it on i.e. connections are cached.
+SET postgres_fdw.keep_connections TO on;
+SELECT 1 FROM ft1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+-- Should output loopback.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+-------------+-------
+ loopback | t
+(1 row)
+
+-- Discard loopback connection.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 2f2d4d171c..0c2ced501e 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -302,6 +302,8 @@ typedef struct
List *already_used; /* expressions already dealt with */
} ec_member_foreign_arg;
+bool keep_connections = true;
+
/*
* SQL functions
*/
@@ -506,6 +508,20 @@ static void merge_fdw_options(PgFdwRelationInfo *fpinfo,
const PgFdwRelationInfo *fpinfo_o,
const PgFdwRelationInfo *fpinfo_i);
+void
+_PG_init(void)
+{
+ DefineCustomBoolVariable("postgres_fdw.keep_connections",
+ "Enables postgres_fdw connection caching.",
+ "When off postgres_fdw will close connections at the end of transaction.",
+ &keep_connections,
+ true,
+ PGC_USERSET,
+ 0,
+ NULL,
+ NULL,
+ NULL);
+}
/*
* Foreign-data wrapper handler function: return a struct with pointers
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index 19ea27a1bc..4d8dd4cd4a 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -124,9 +124,12 @@ typedef struct PgFdwRelationInfo
int relation_index;
} PgFdwRelationInfo;
+extern bool keep_connections;
+
/* in postgres_fdw.c */
extern int set_transmission_modes(void);
extern void reset_transmission_modes(int nestlevel);
+extern void _PG_init(void);
/* in connection.c */
extern PGconn *GetConnection(UserMapping *user, bool will_prep_stmt);
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 3465cc0f56..8a16dc40aa 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -2871,3 +2871,33 @@ DROP SERVER temploopback2 CASCADE;
-- Should output 2 rows of each null server name with valid false.
SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
COMMIT;
+
+-- ===================================================================
+-- Test postgres_fdw.keep_connections GUC
+-- ===================================================================
+
+-- By default, keep_connections GUC is on i.e. local session caches all the
+-- foreign server connections.
+SHOW postgres_fdw.keep_connections;
+
+-- Set it off i.e. the cached connections which are used after this setting are
+-- disconnected at the end of respective xacts.
+SET postgres_fdw.keep_connections TO off;
+
+-- Make connection using loopback server, connection should not be cached as
+-- the GUC is off.
+SELECT 1 FROM ft1 LIMIT 1;
+
+-- Should output nothing.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+
+-- Set it on i.e. connections are cached.
+SET postgres_fdw.keep_connections TO on;
+
+SELECT 1 FROM ft1 LIMIT 1;
+
+-- Should output loopback.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+
+-- Discard loopback connection.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml
index 1da9599f59..49344efff2 100644
--- a/doc/src/sgml/postgres-fdw.sgml
+++ b/doc/src/sgml/postgres-fdw.sgml
@@ -555,6 +555,42 @@ postgres=# SELECT * FROM postgres_fdw_disconnect();
</sect2>
+<sect2>
+ <title>Configuration Parameters</title>
+
+ <variablelist>
+ <varlistentry>
+
+ <term>
+ <varname>postgres_fdw.keep_connections</varname> (<type>boolean</type>)
+ <indexterm>
+ <primary><varname>postgres_fdw.keep_connections</varname> configuration parameter</primary>
+ </indexterm>
+ </term>
+
+ <listitem>
+
+ <para>
+ Allows <filename>postgres_fdw</filename> to keep or discard the
+ connection made to the foreign server by the local session. Default is
+ <literal>on</literal>. When set to <literal>off</literal> the local
+ session doesn't keep the connections made to the foreign servers. Each
+ connection is discarded at the end of transaction in which it is used.
+ </para>
+
+ <para>
+ Note that setting <varname>postgres_fdw.keep_connections</varname> to
+ <literal>off</literal> does not discard any previously made and still open
+ connections immediately. They will be closed only at the end of future
+ transactions, which operated on them. To close all connections
+ immediately use <function>postgres_fdw_disconnect</function> function.
+ </para>
+
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </sect2>
+
<sect2>
<title>Connection Management</title>
@@ -573,12 +609,18 @@ postgres=# SELECT * FROM postgres_fdw_disconnect();
the remote servers are kept idle until they are re-used by the local session.
This may waste resources if those connections are not frequently used by the
local session. To address this, the <filename>postgres_fdw</filename>
- provides following way to remove the connections to the remote servers and
+ provides following ways to remove the connections to the remote servers and
so the remote sessions:
<function>postgres_fdw_disconnect()</function> to discard all the
connections or <function>postgres_fdw_disconnect(text)</function>
to discard the connection associated with the given foreign server.
+
+ A configuration parameter, <varname>postgres_fdw.keep_connections</varname>,
+ default being <literal>on</literal>, when set to <literal>off</literal>, the
+ local session doesn't keep remote connections that are made to the foreign
+ servers. Each connection is discarded at the end of transaction in which it
+ is used.
</para>
</sect2>
--
2.25.1
From a67378b0f0d154e0c59381e39d7f0edef90dd064 Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddy@enterprisedb.com>
Date: Sat, 16 Jan 2021 11:15:42 +0530
Subject: [PATCH v10 3/3] postgres_fdw server level option, keep_connection to not
cache connection
This patch adds a new server level option, keep_connection,
default being on, when set to off, the local session doesn't cache
the connections associated with the foreign server.
---
contrib/postgres_fdw/connection.c | 35 ++++++++++++---
.../postgres_fdw/expected/postgres_fdw.out | 44 ++++++++++++++++++-
contrib/postgres_fdw/option.c | 9 +++-
contrib/postgres_fdw/sql/postgres_fdw.sql | 26 +++++++++++
doc/src/sgml/postgres-fdw.sgml | 43 ++++++++++++++++++
5 files changed, 150 insertions(+), 7 deletions(-)
diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c
index 260e956195..1e305312f7 100644
--- a/contrib/postgres_fdw/connection.c
+++ b/contrib/postgres_fdw/connection.c
@@ -62,6 +62,8 @@ typedef struct ConnCacheEntry
Oid serverid; /* foreign server OID used to get server name */
uint32 server_hashvalue; /* hash value of foreign server OID */
uint32 mapping_hashvalue; /* hash value of user mapping OID */
+ /* Keep or discard this connection at the end of xact */
+ bool keep_connection;
} ConnCacheEntry;
/*
@@ -125,6 +127,8 @@ GetConnection(UserMapping *user, bool will_prep_stmt)
ConnCacheEntry *entry;
ConnCacheKey key;
MemoryContext ccxt = CurrentMemoryContext;
+ ListCell *lc;
+ ForeignServer *server;
/* First time through, initialize connection cache hashtable */
if (ConnectionHash == NULL)
@@ -267,6 +271,15 @@ GetConnection(UserMapping *user, bool will_prep_stmt)
begin_remote_xact(entry);
}
+ server = GetForeignServer(user->serverid);
+ foreach(lc, server->options)
+ {
+ DefElem *def = (DefElem *) lfirst(lc);
+
+ if (strcmp(def->defname, "keep_connection") == 0)
+ entry->keep_connection = defGetBoolean(def);
+ }
+
/* Remember if caller will prepare statements */
entry->have_prep_stmt |= will_prep_stmt;
@@ -291,6 +304,7 @@ make_new_connection(ConnCacheEntry *entry, UserMapping *user)
entry->changing_xact_state = false;
entry->invalidated = false;
entry->serverid = server->serverid;
+ entry->keep_connection = true;
entry->server_hashvalue =
GetSysCacheHashValue1(FOREIGNSERVEROID,
ObjectIdGetDatum(server->serverid));
@@ -962,15 +976,18 @@ pgfdw_xact_callback(XactEvent event, void *arg)
/*
* If the connection isn't in a good idle state or it is marked as
- * invalid or keep_connections GUC is false and this connection is used
- * in current xact, then discard it to recover. Next GetConnection will
- * open a new connection.
+ * invalid or this connection is used in current xact and
+ * keep_connections GUC is false or GUC is true but the server level
+ * option is false, then discard it to recover. Next GetConnection will
+ * open a new connection. Note that keep_connections GUC overrides the
+ * server level keep_connection option.
*/
if (PQstatus(entry->conn) != CONNECTION_OK ||
PQtransactionStatus(entry->conn) != PQTRANS_IDLE ||
entry->changing_xact_state ||
entry->invalidated ||
- (used_in_current_xact && !keep_connections))
+ (used_in_current_xact &&
+ (!keep_connections || !entry->keep_connection)))
{
elog(DEBUG3, "discarding connection %p", entry->conn);
disconnect_pg_server(entry);
@@ -1124,7 +1141,15 @@ pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue)
if (!ConnectionHash)
return;
- /* ConnectionHash must exist already, if we're registered */
+ /*
+ * Since we can discard ConnectionHash with postgres_fdw_disconnect, we may
+ * have a NULL ConnectionHash. So return in that case. We do not need to
+ * invalidate the cache entries as the cache itself would have discarded
+ * with postgres_fdw_disconnect.
+ */
+ if (!ConnectionHash)
+ return;
+
hash_seq_init(&scan, ConnectionHash);
while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
{
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index a655c7025f..1057e44a6a 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8933,7 +8933,7 @@ DO $d$
END;
$d$;
ERROR: invalid option "password"
-HINT: Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size
+HINT: Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size, keep_connection
CONTEXT: SQL statement "ALTER SERVER loopback_nopw OPTIONS (ADD password 'dummypw')"
PL/pgSQL function inline_code_block line 3 at EXECUTE
-- If we add a password for our user mapping instead, we should get a different
@@ -9499,3 +9499,45 @@ SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
t
(1 row)
+-- ===================================================================
+-- Test foreign server level option keep_connection
+-- ===================================================================
+-- By default, the connections associated with foreign server are cached i.e.
+-- keep_connection option is on. Set it to off.
+ALTER SERVER loopback OPTIONS (keep_connection 'off');
+-- loopback server connection is closed by the local session at the end of xact
+-- as the keep_connection was set to off.
+SELECT 1 FROM ft1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+-- Should output nothing.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+-------------+-------
+(0 rows)
+
+ALTER SERVER loopback OPTIONS (SET keep_connection 'on');
+-- loopback server connection should get cached.
+SELECT 1 FROM ft1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+-- Should output loopback.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name | valid
+-------------+-------
+ loopback | t
+(1 row)
+
+-- Discard loopback connection.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+ postgres_fdw_disconnect
+-------------------------
+ t
+(1 row)
+
diff --git a/contrib/postgres_fdw/option.c b/contrib/postgres_fdw/option.c
index 1fec3c3eea..e8a144c06c 100644
--- a/contrib/postgres_fdw/option.c
+++ b/contrib/postgres_fdw/option.c
@@ -107,7 +107,8 @@ postgres_fdw_validator(PG_FUNCTION_ARGS)
* Validate option value, when we can do so without any context.
*/
if (strcmp(def->defname, "use_remote_estimate") == 0 ||
- strcmp(def->defname, "updatable") == 0)
+ strcmp(def->defname, "updatable") == 0 ||
+ strcmp(def->defname, "keep_connection") == 0)
{
/* these accept only boolean values */
(void) defGetBoolean(def);
@@ -213,6 +214,12 @@ InitPgFdwOptions(void)
{"sslcert", UserMappingRelationId, true},
{"sslkey", UserMappingRelationId, true},
+ /*
+ * If true, cache the connection associated with this server, otherwise
+ * remove it at the end of the xact. Default is true.
+ */
+ {"keep_connection", ForeignServerRelationId, false},
+
{NULL, InvalidOid, false}
};
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 8a16dc40aa..c9b780abe8 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -2901,3 +2901,29 @@ SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
-- Discard loopback connection.
SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
+
+-- ===================================================================
+-- Test foreign server level option keep_connection
+-- ===================================================================
+
+-- By default, the connections associated with foreign server are cached i.e.
+-- keep_connection option is on. Set it to off.
+ALTER SERVER loopback OPTIONS (keep_connection 'off');
+
+-- loopback server connection is closed by the local session at the end of xact
+-- as the keep_connection was set to off.
+SELECT 1 FROM ft1 LIMIT 1;
+
+-- Should output nothing.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+
+ALTER SERVER loopback OPTIONS (SET keep_connection 'on');
+
+-- loopback server connection should get cached.
+SELECT 1 FROM ft1 LIMIT 1;
+
+-- Should output loopback.
+SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+
+-- Discard loopback connection.
+SELECT * FROM postgres_fdw_disconnect(); /* TRUE */
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml
index 49344efff2..f554351dd0 100644
--- a/doc/src/sgml/postgres-fdw.sgml
+++ b/doc/src/sgml/postgres-fdw.sgml
@@ -477,6 +477,35 @@ OPTIONS (ADD password_required 'false');
</para>
</sect3>
+
+ <sect3>
+ <title>Connection Management Options</title>
+
+ <para>
+ By default the foreign server connections made with
+ <filename>postgres_fdw</filename> are kept in local session for re-use.
+ This may be overridden using the following
+ <xref linkend="sql-createserver"/> option:
+ </para>
+
+ <variablelist>
+
+ <varlistentry>
+ <term><literal>keep_connection</literal></term>
+ <listitem>
+ <para>
+ This option controls whether <filename>postgres_fdw</filename> keeps the
+ server connection that is made with a specific foreign server. It can be
+ specified for a foreign server. Default is <literal>on</literal>. When
+ set to <literal>off</literal>, the associated foreign server connection
+ is discarded at the end of the transaction.
+ </para>
+
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+ </sect3>
</sect2>
<sect2>
@@ -578,6 +607,14 @@ postgres=# SELECT * FROM postgres_fdw_disconnect();
connection is discarded at the end of transaction in which it is used.
</para>
+ <para>
+ <varname>postgres_fdw.keep_connections</varname> configuration parameter
+ overrides the server level <literal>keep_connection</literal> option.
+ Which means that when the configuration parameter is set to
+ <literal>on</literal>, irrespective of the server option
+ <literal>keep_connection</literal> setting, the connections are discarded.
+ </para>
+
<para>
Note that setting <varname>postgres_fdw.keep_connections</varname> to
<literal>off</literal> does not discard any previously made and still open
@@ -621,6 +658,12 @@ postgres=# SELECT * FROM postgres_fdw_disconnect();
local session doesn't keep remote connections that are made to the foreign
servers. Each connection is discarded at the end of transaction in which it
is used.
+
+ A server level option, <literal>keep_connection</literal> that is used with
+ <xref linkend="sql-createserver"/>. Default being <literal>on</literal>,
+ when set to <literal>off</literal> the local session doesn't keep remote
+ connection associated with the foreign server. The connection is discarded
+ at the end of the transaction.
</para>
</sect2>
--
2.25.1
