Adding upstream version 15.4.upstream/15.4upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3094 insertions, 0 deletions

diff --git a/contrib/dblink/dblink.c b/contrib/dblink/dblink.c
new file mode 100644
index 0000000..0cc339e
--- /dev/null
+++ b/contrib/dblink/dblink.c
@@ -0,0 +1,3094 @@
+/*
+ * dblink.c
+ *
+ * Functions returning results from a remote database
+ *
+ * Joe Conway <mail@joeconway.com>
+ * And contributors:
+ * Darko Prenosil <Darko.Prenosil@finteh.hr>
+ * Shridhar Daithankar <shridhar_daithankar@persistent.co.in>
+ *
+ * contrib/dblink/dblink.c
+ * Copyright (c) 2001-2022, PostgreSQL Global Development Group
+ * ALL RIGHTS RESERVED;
+ *
+ * Permission to use, copy, modify, and distribute this software and its
+ * documentation for any purpose, without fee, and without a written agreement
+ * is hereby granted, provided that the above copyright notice and this
+ * paragraph and the following two paragraphs appear in all copies.
+ *
+ * IN NO EVENT SHALL THE AUTHOR OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
+ * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+ * DOCUMENTATION, EVEN IF THE AUTHOR OR DISTRIBUTORS HAVE BEEN ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ * THE AUTHOR AND DISTRIBUTORS SPECIFICALLY DISCLAIMS ANY WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE AUTHOR AND DISTRIBUTORS HAS NO OBLIGATIONS TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ */
+#include "postgres.h"
+
+#include <limits.h>
+
+#include "access/htup_details.h"
+#include "access/relation.h"
+#include "access/reloptions.h"
+#include "access/table.h"
+#include "catalog/namespace.h"
+#include "catalog/pg_foreign_data_wrapper.h"
+#include "catalog/pg_foreign_server.h"
+#include "catalog/pg_type.h"
+#include "catalog/pg_user_mapping.h"
+#include "executor/spi.h"
+#include "foreign/foreign.h"
+#include "funcapi.h"
+#include "lib/stringinfo.h"
+#include "libpq-fe.h"
+#include "mb/pg_wchar.h"
+#include "miscadmin.h"
+#include "parser/scansup.h"
+#include "utils/acl.h"
+#include "utils/builtins.h"
+#include "utils/fmgroids.h"
+#include "utils/guc.h"
+#include "utils/lsyscache.h"
+#include "utils/memutils.h"
+#include "utils/rel.h"
+#include "utils/varlena.h"
+
+PG_MODULE_MAGIC;
+
+typedef struct remoteConn
+{
+	PGconn	   *conn;			/* Hold the remote connection */
+	int			openCursorCount;	/* The number of open cursors */
+	bool		newXactForCursor;	/* Opened a transaction for a cursor */
+} remoteConn;
+
+typedef struct storeInfo
+{
+	FunctionCallInfo fcinfo;
+	Tuplestorestate *tuplestore;
+	AttInMetadata *attinmeta;
+	MemoryContext tmpcontext;
+	char	  **cstrs;
+	/* temp storage for results to avoid leaks on exception */
+	PGresult   *last_res;
+	PGresult   *cur_res;
+} storeInfo;
+
+/*
+ * Internal declarations
+ */
+static Datum dblink_record_internal(FunctionCallInfo fcinfo, bool is_async);
+static void prepTuplestoreResult(FunctionCallInfo fcinfo);
+static void materializeResult(FunctionCallInfo fcinfo, PGconn *conn,
+							  PGresult *res);
+static void materializeQueryResult(FunctionCallInfo fcinfo,
+								   PGconn *conn,
+								   const char *conname,
+								   const char *sql,
+								   bool fail);
+static PGresult *storeQueryResult(volatile storeInfo *sinfo, PGconn *conn, const char *sql);
+static void storeRow(volatile storeInfo *sinfo, PGresult *res, bool first);
+static remoteConn *getConnectionByName(const char *name);
+static HTAB *createConnHash(void);
+static void createNewConnection(const char *name, remoteConn *rconn);
+static void deleteConnection(const char *name);
+static char **get_pkey_attnames(Relation rel, int16 *indnkeyatts);
+static char **get_text_array_contents(ArrayType *array, int *numitems);
+static char *get_sql_insert(Relation rel, int *pkattnums, int pknumatts, char **src_pkattvals, char **tgt_pkattvals);
+static char *get_sql_delete(Relation rel, int *pkattnums, int pknumatts, char **tgt_pkattvals);
+static char *get_sql_update(Relation rel, int *pkattnums, int pknumatts, char **src_pkattvals, char **tgt_pkattvals);
+static char *quote_ident_cstr(char *rawstr);
+static int	get_attnum_pk_pos(int *pkattnums, int pknumatts, int key);
+static HeapTuple get_tuple_of_interest(Relation rel, int *pkattnums, int pknumatts, char **src_pkattvals);
+static Relation get_rel_from_relname(text *relname_text, LOCKMODE lockmode, AclMode aclmode);
+static char *generate_relation_name(Relation rel);
+static void dblink_connstr_check(const char *connstr);
+static void dblink_security_check(PGconn *conn, remoteConn *rconn);
+static void dblink_res_error(PGconn *conn, const char *conname, PGresult *res,
+							 bool fail, const char *fmt,...) pg_attribute_printf(5, 6);
+static char *get_connect_string(const char *servername);
+static char *escape_param_str(const char *from);
+static void validate_pkattnums(Relation rel,
+							   int2vector *pkattnums_arg, int32 pknumatts_arg,
+							   int **pkattnums, int *pknumatts);
+static bool is_valid_dblink_option(const PQconninfoOption *options,
+								   const char *option, Oid context);
+static int	applyRemoteGucs(PGconn *conn);
+static void restoreLocalGucs(int nestlevel);
+
+/* Global */
+static remoteConn *pconn = NULL;
+static HTAB *remoteConnHash = NULL;
+
+/*
+ *	Following is list that holds multiple remote connections.
+ *	Calling convention of each dblink function changes to accept
+ *	connection name as the first parameter. The connection list is
+ *	much like ecpg e.g. a mapping between a name and a PGconn object.
+ */
+
+typedef struct remoteConnHashEnt
+{
+	char		name[NAMEDATALEN];
+	remoteConn *rconn;
+} remoteConnHashEnt;
+
+/* initial number of connection hashes */
+#define NUMCONN 16
+
+static char *
+xpstrdup(const char *in)
+{
+	if (in == NULL)
+		return NULL;
+	return pstrdup(in);
+}
+
+static void
+pg_attribute_noreturn()
+dblink_res_internalerror(PGconn *conn, PGresult *res, const char *p2)
+{
+	char	   *msg = pchomp(PQerrorMessage(conn));
+
+	if (res)
+		PQclear(res);
+	elog(ERROR, "%s: %s", p2, msg);
+}
+
+static void
+pg_attribute_noreturn()
+dblink_conn_not_avail(const char *conname)
+{
+	if (conname)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONNECTION_DOES_NOT_EXIST),
+				 errmsg("connection \"%s\" not available", conname)));
+	else
+		ereport(ERROR,
+				(errcode(ERRCODE_CONNECTION_DOES_NOT_EXIST),
+				 errmsg("connection not available")));
+}
+
+static void
+dblink_get_conn(char *conname_or_str,
+				PGconn *volatile *conn_p, char **conname_p, volatile bool *freeconn_p)
+{
+	remoteConn *rconn = getConnectionByName(conname_or_str);
+	PGconn	   *conn;
+	char	   *conname;
+	bool		freeconn;
+
+	if (rconn)
+	{
+		conn = rconn->conn;
+		conname = conname_or_str;
+		freeconn = false;
+	}
+	else
+	{
+		const char *connstr;
+
+		connstr = get_connect_string(conname_or_str);
+		if (connstr == NULL)
+			connstr = conname_or_str;
+		dblink_connstr_check(connstr);
+
+		/*
+		 * We must obey fd.c's limit on non-virtual file descriptors.  Assume
+		 * that a PGconn represents one long-lived FD.  (Doing this here also
+		 * ensures that VFDs are closed if needed to make room.)
+		 */
+		if (!AcquireExternalFD())
+		{
+#ifndef WIN32					/* can't write #if within ereport() macro */
+			ereport(ERROR,
+					(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
+					 errmsg("could not establish connection"),
+					 errdetail("There are too many open files on the local server."),
+					 errhint("Raise the server's max_files_per_process and/or \"ulimit -n\" limits.")));
+#else
+			ereport(ERROR,
+					(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
+					 errmsg("could not establish connection"),
+					 errdetail("There are too many open files on the local server."),
+					 errhint("Raise the server's max_files_per_process setting.")));
+#endif
+		}
+
+		/* OK to make connection */
+		conn = PQconnectdb(connstr);
+
+		if (PQstatus(conn) == CONNECTION_BAD)
+		{
+			char	   *msg = pchomp(PQerrorMessage(conn));
+
+			PQfinish(conn);
+			ReleaseExternalFD();
+			ereport(ERROR,
+					(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
+					 errmsg("could not establish connection"),
+					 errdetail_internal("%s", msg)));
+		}
+		dblink_security_check(conn, rconn);
+		if (PQclientEncoding(conn) != GetDatabaseEncoding())
+			PQsetClientEncoding(conn, GetDatabaseEncodingName());
+		freeconn = true;
+		conname = NULL;
+	}
+
+	*conn_p = conn;
+	*conname_p = conname;
+	*freeconn_p = freeconn;
+}
+
+static PGconn *
+dblink_get_named_conn(const char *conname)
+{
+	remoteConn *rconn = getConnectionByName(conname);
+
+	if (rconn)
+		return rconn->conn;
+
+	dblink_conn_not_avail(conname);
+	return NULL;				/* keep compiler quiet */
+}
+
+static void
+dblink_init(void)
+{
+	if (!pconn)
+	{
+		pconn = (remoteConn *) MemoryContextAlloc(TopMemoryContext, sizeof(remoteConn));
+		pconn->conn = NULL;
+		pconn->openCursorCount = 0;
+		pconn->newXactForCursor = false;
+	}
+}
+
+/*
+ * Create a persistent connection to another database
+ */
+PG_FUNCTION_INFO_V1(dblink_connect);
+Datum
+dblink_connect(PG_FUNCTION_ARGS)
+{
+	char	   *conname_or_str = NULL;
+	char	   *connstr = NULL;
+	char	   *connname = NULL;
+	char	   *msg;
+	PGconn	   *conn = NULL;
+	remoteConn *rconn = NULL;
+
+	dblink_init();
+
+	if (PG_NARGS() == 2)
+	{
+		conname_or_str = text_to_cstring(PG_GETARG_TEXT_PP(1));
+		connname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+	}
+	else if (PG_NARGS() == 1)
+		conname_or_str = text_to_cstring(PG_GETARG_TEXT_PP(0));
+
+	if (connname)
+	{
+		rconn = (remoteConn *) MemoryContextAlloc(TopMemoryContext,
+												  sizeof(remoteConn));
+		rconn->conn = NULL;
+		rconn->openCursorCount = 0;
+		rconn->newXactForCursor = false;
+	}
+
+	/* first check for valid foreign data server */
+	connstr = get_connect_string(conname_or_str);
+	if (connstr == NULL)
+		connstr = conname_or_str;
+
+	/* check password in connection string if not superuser */
+	dblink_connstr_check(connstr);
+
+	/*
+	 * We must obey fd.c's limit on non-virtual file descriptors.  Assume that
+	 * a PGconn represents one long-lived FD.  (Doing this here also ensures
+	 * that VFDs are closed if needed to make room.)
+	 */
+	if (!AcquireExternalFD())
+	{
+#ifndef WIN32					/* can't write #if within ereport() macro */
+		ereport(ERROR,
+				(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
+				 errmsg("could not establish connection"),
+				 errdetail("There are too many open files on the local server."),
+				 errhint("Raise the server's max_files_per_process and/or \"ulimit -n\" limits.")));
+#else
+		ereport(ERROR,
+				(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
+				 errmsg("could not establish connection"),
+				 errdetail("There are too many open files on the local server."),
+				 errhint("Raise the server's max_files_per_process setting.")));
+#endif
+	}
+
+	/* OK to make connection */
+	conn = PQconnectdb(connstr);
+
+	if (PQstatus(conn) == CONNECTION_BAD)
+	{
+		msg = pchomp(PQerrorMessage(conn));
+		PQfinish(conn);
+		ReleaseExternalFD();
+		if (rconn)
+			pfree(rconn);
+
+		ereport(ERROR,
+				(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
+				 errmsg("could not establish connection"),
+				 errdetail_internal("%s", msg)));
+	}
+
+	/* check password actually used if not superuser */
+	dblink_security_check(conn, rconn);
+
+	/* attempt to set client encoding to match server encoding, if needed */
+	if (PQclientEncoding(conn) != GetDatabaseEncoding())
+		PQsetClientEncoding(conn, GetDatabaseEncodingName());
+
+	if (connname)
+	{
+		rconn->conn = conn;
+		createNewConnection(connname, rconn);
+	}
+	else
+	{
+		if (pconn->conn)
+		{
+			PQfinish(pconn->conn);
+			ReleaseExternalFD();
+		}
+		pconn->conn = conn;
+	}
+
+	PG_RETURN_TEXT_P(cstring_to_text("OK"));
+}
+
+/*
+ * Clear a persistent connection to another database
+ */
+PG_FUNCTION_INFO_V1(dblink_disconnect);
+Datum
+dblink_disconnect(PG_FUNCTION_ARGS)
+{
+	char	   *conname = NULL;
+	remoteConn *rconn = NULL;
+	PGconn	   *conn = NULL;
+
+	dblink_init();
+
+	if (PG_NARGS() == 1)
+	{
+		conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+		rconn = getConnectionByName(conname);
+		if (rconn)
+			conn = rconn->conn;
+	}
+	else
+		conn = pconn->conn;
+
+	if (!conn)
+		dblink_conn_not_avail(conname);
+
+	PQfinish(conn);
+	ReleaseExternalFD();
+	if (rconn)
+	{
+		deleteConnection(conname);
+		pfree(rconn);
+	}
+	else
+		pconn->conn = NULL;
+
+	PG_RETURN_TEXT_P(cstring_to_text("OK"));
+}
+
+/*
+ * opens a cursor using a persistent connection
+ */
+PG_FUNCTION_INFO_V1(dblink_open);
+Datum
+dblink_open(PG_FUNCTION_ARGS)
+{
+	PGresult   *res = NULL;
+	PGconn	   *conn;
+	char	   *curname = NULL;
+	char	   *sql = NULL;
+	char	   *conname = NULL;
+	StringInfoData buf;
+	remoteConn *rconn = NULL;
+	bool		fail = true;	/* default to backward compatible behavior */
+
+	dblink_init();
+	initStringInfo(&buf);
+
+	if (PG_NARGS() == 2)
+	{
+		/* text,text */
+		curname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+		sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
+		rconn = pconn;
+	}
+	else if (PG_NARGS() == 3)
+	{
+		/* might be text,text,text or text,text,bool */
+		if (get_fn_expr_argtype(fcinfo->flinfo, 2) == BOOLOID)
+		{
+			curname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+			sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
+			fail = PG_GETARG_BOOL(2);
+			rconn = pconn;
+		}
+		else
+		{
+			conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+			curname = text_to_cstring(PG_GETARG_TEXT_PP(1));
+			sql = text_to_cstring(PG_GETARG_TEXT_PP(2));
+			rconn = getConnectionByName(conname);
+		}
+	}
+	else if (PG_NARGS() == 4)
+	{
+		/* text,text,text,bool */
+		conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+		curname = text_to_cstring(PG_GETARG_TEXT_PP(1));
+		sql = text_to_cstring(PG_GETARG_TEXT_PP(2));
+		fail = PG_GETARG_BOOL(3);
+		rconn = getConnectionByName(conname);
+	}
+
+	if (!rconn || !rconn->conn)
+		dblink_conn_not_avail(conname);
+
+	conn = rconn->conn;
+
+	/* If we are not in a transaction, start one */
+	if (PQtransactionStatus(conn) == PQTRANS_IDLE)
+	{
+		res = PQexec(conn, "BEGIN");
+		if (PQresultStatus(res) != PGRES_COMMAND_OK)
+			dblink_res_internalerror(conn, res, "begin error");
+		PQclear(res);
+		rconn->newXactForCursor = true;
+
+		/*
+		 * Since transaction state was IDLE, we force cursor count to
+		 * initially be 0. This is needed as a previous ABORT might have wiped
+		 * out our transaction without maintaining the cursor count for us.
+		 */
+		rconn->openCursorCount = 0;
+	}
+
+	/* if we started a transaction, increment cursor count */
+	if (rconn->newXactForCursor)
+		(rconn->openCursorCount)++;
+
+	appendStringInfo(&buf, "DECLARE %s CURSOR FOR %s", curname, sql);
+	res = PQexec(conn, buf.data);
+	if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
+	{
+		dblink_res_error(conn, conname, res, fail,
+						 "while opening cursor \"%s\"", curname);
+		PG_RETURN_TEXT_P(cstring_to_text("ERROR"));
+	}
+
+	PQclear(res);
+	PG_RETURN_TEXT_P(cstring_to_text("OK"));
+}
+
+/*
+ * closes a cursor
+ */
+PG_FUNCTION_INFO_V1(dblink_close);
+Datum
+dblink_close(PG_FUNCTION_ARGS)
+{
+	PGconn	   *conn;
+	PGresult   *res = NULL;
+	char	   *curname = NULL;
+	char	   *conname = NULL;
+	StringInfoData buf;
+	remoteConn *rconn = NULL;
+	bool		fail = true;	/* default to backward compatible behavior */
+
+	dblink_init();
+	initStringInfo(&buf);
+
+	if (PG_NARGS() == 1)
+	{
+		/* text */
+		curname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+		rconn = pconn;
+	}
+	else if (PG_NARGS() == 2)
+	{
+		/* might be text,text or text,bool */
+		if (get_fn_expr_argtype(fcinfo->flinfo, 1) == BOOLOID)
+		{
+			curname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+			fail = PG_GETARG_BOOL(1);
+			rconn = pconn;
+		}
+		else
+		{
+			conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+			curname = text_to_cstring(PG_GETARG_TEXT_PP(1));
+			rconn = getConnectionByName(conname);
+		}
+	}
+	if (PG_NARGS() == 3)
+	{
+		/* text,text,bool */
+		conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+		curname = text_to_cstring(PG_GETARG_TEXT_PP(1));
+		fail = PG_GETARG_BOOL(2);
+		rconn = getConnectionByName(conname);
+	}
+
+	if (!rconn || !rconn->conn)
+		dblink_conn_not_avail(conname);
+
+	conn = rconn->conn;
+
+	appendStringInfo(&buf, "CLOSE %s", curname);
+
+	/* close the cursor */
+	res = PQexec(conn, buf.data);
+	if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
+	{
+		dblink_res_error(conn, conname, res, fail,
+						 "while closing cursor \"%s\"", curname);
+		PG_RETURN_TEXT_P(cstring_to_text("ERROR"));
+	}
+
+	PQclear(res);
+
+	/* if we started a transaction, decrement cursor count */
+	if (rconn->newXactForCursor)
+	{
+		(rconn->openCursorCount)--;
+
+		/* if count is zero, commit the transaction */
+		if (rconn->openCursorCount == 0)
+		{
+			rconn->newXactForCursor = false;
+
+			res = PQexec(conn, "COMMIT");
+			if (PQresultStatus(res) != PGRES_COMMAND_OK)
+				dblink_res_internalerror(conn, res, "commit error");
+			PQclear(res);
+		}
+	}
+
+	PG_RETURN_TEXT_P(cstring_to_text("OK"));
+}
+
+/*
+ * Fetch results from an open cursor
+ */
+PG_FUNCTION_INFO_V1(dblink_fetch);
+Datum
+dblink_fetch(PG_FUNCTION_ARGS)
+{
+	PGresult   *res = NULL;
+	char	   *conname = NULL;
+	remoteConn *rconn = NULL;
+	PGconn	   *conn = NULL;
+	StringInfoData buf;
+	char	   *curname = NULL;
+	int			howmany = 0;
+	bool		fail = true;	/* default to backward compatible */
+
+	prepTuplestoreResult(fcinfo);
+
+	dblink_init();
+
+	if (PG_NARGS() == 4)
+	{
+		/* text,text,int,bool */
+		conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+		curname = text_to_cstring(PG_GETARG_TEXT_PP(1));
+		howmany = PG_GETARG_INT32(2);
+		fail = PG_GETARG_BOOL(3);
+
+		rconn = getConnectionByName(conname);
+		if (rconn)
+			conn = rconn->conn;
+	}
+	else if (PG_NARGS() == 3)
+	{
+		/* text,text,int or text,int,bool */
+		if (get_fn_expr_argtype(fcinfo->flinfo, 2) == BOOLOID)
+		{
+			curname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+			howmany = PG_GETARG_INT32(1);
+			fail = PG_GETARG_BOOL(2);
+			conn = pconn->conn;
+		}
+		else
+		{
+			conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+			curname = text_to_cstring(PG_GETARG_TEXT_PP(1));
+			howmany = PG_GETARG_INT32(2);
+
+			rconn = getConnectionByName(conname);
+			if (rconn)
+				conn = rconn->conn;
+		}
+	}
+	else if (PG_NARGS() == 2)
+	{
+		/* text,int */
+		curname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+		howmany = PG_GETARG_INT32(1);
+		conn = pconn->conn;
+	}
+
+	if (!conn)
+		dblink_conn_not_avail(conname);
+
+	initStringInfo(&buf);
+	appendStringInfo(&buf, "FETCH %d FROM %s", howmany, curname);
+
+	/*
+	 * Try to execute the query.  Note that since libpq uses malloc, the
+	 * PGresult will be long-lived even though we are still in a short-lived
+	 * memory context.
+	 */
+	res = PQexec(conn, buf.data);
+	if (!res ||
+		(PQresultStatus(res) != PGRES_COMMAND_OK &&
+		 PQresultStatus(res) != PGRES_TUPLES_OK))
+	{
+		dblink_res_error(conn, conname, res, fail,
+						 "while fetching from cursor \"%s\"", curname);
+		return (Datum) 0;
+	}
+	else if (PQresultStatus(res) == PGRES_COMMAND_OK)
+	{
+		/* cursor does not exist - closed already or bad name */
+		PQclear(res);
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_CURSOR_NAME),
+				 errmsg("cursor \"%s\" does not exist", curname)));
+	}
+
+	materializeResult(fcinfo, conn, res);
+	return (Datum) 0;
+}
+
+/*
+ * Note: this is the new preferred version of dblink
+ */
+PG_FUNCTION_INFO_V1(dblink_record);
+Datum
+dblink_record(PG_FUNCTION_ARGS)
+{
+	return dblink_record_internal(fcinfo, false);
+}
+
+PG_FUNCTION_INFO_V1(dblink_send_query);
+Datum
+dblink_send_query(PG_FUNCTION_ARGS)
+{
+	PGconn	   *conn;
+	char	   *sql;
+	int			retval;
+
+	if (PG_NARGS() == 2)
+	{
+		conn = dblink_get_named_conn(text_to_cstring(PG_GETARG_TEXT_PP(0)));
+		sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	}
+	else
+		/* shouldn't happen */
+		elog(ERROR, "wrong number of arguments");
+
+	/* async query send */
+	retval = PQsendQuery(conn, sql);
+	if (retval != 1)
+		elog(NOTICE, "could not send query: %s", pchomp(PQerrorMessage(conn)));
+
+	PG_RETURN_INT32(retval);
+}
+
+PG_FUNCTION_INFO_V1(dblink_get_result);
+Datum
+dblink_get_result(PG_FUNCTION_ARGS)
+{
+	return dblink_record_internal(fcinfo, true);
+}
+
+static Datum
+dblink_record_internal(FunctionCallInfo fcinfo, bool is_async)
+{
+	PGconn	   *volatile conn = NULL;
+	volatile bool freeconn = false;
+
+	prepTuplestoreResult(fcinfo);
+
+	dblink_init();
+
+	PG_TRY();
+	{
+		char	   *sql = NULL;
+		char	   *conname = NULL;
+		bool		fail = true;	/* default to backward compatible */
+
+		if (!is_async)
+		{
+			if (PG_NARGS() == 3)
+			{
+				/* text,text,bool */
+				conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+				sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
+				fail = PG_GETARG_BOOL(2);
+				dblink_get_conn(conname, &conn, &conname, &freeconn);
+			}
+			else if (PG_NARGS() == 2)
+			{
+				/* text,text or text,bool */
+				if (get_fn_expr_argtype(fcinfo->flinfo, 1) == BOOLOID)
+				{
+					sql = text_to_cstring(PG_GETARG_TEXT_PP(0));
+					fail = PG_GETARG_BOOL(1);
+					conn = pconn->conn;
+				}
+				else
+				{
+					conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+					sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
+					dblink_get_conn(conname, &conn, &conname, &freeconn);
+				}
+			}
+			else if (PG_NARGS() == 1)
+			{
+				/* text */
+				conn = pconn->conn;
+				sql = text_to_cstring(PG_GETARG_TEXT_PP(0));
+			}
+			else
+				/* shouldn't happen */
+				elog(ERROR, "wrong number of arguments");
+		}
+		else					/* is_async */
+		{
+			/* get async result */
+			conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+
+			if (PG_NARGS() == 2)
+			{
+				/* text,bool */
+				fail = PG_GETARG_BOOL(1);
+				conn = dblink_get_named_conn(conname);
+			}
+			else if (PG_NARGS() == 1)
+			{
+				/* text */
+				conn = dblink_get_named_conn(conname);
+			}
+			else
+				/* shouldn't happen */
+				elog(ERROR, "wrong number of arguments");
+		}
+
+		if (!conn)
+			dblink_conn_not_avail(conname);
+
+		if (!is_async)
+		{
+			/* synchronous query, use efficient tuple collection method */
+			materializeQueryResult(fcinfo, conn, conname, sql, fail);
+		}
+		else
+		{
+			/* async result retrieval, do it the old way */
+			PGresult   *res = PQgetResult(conn);
+
+			/* NULL means we're all done with the async results */
+			if (res)
+			{
+				if (PQresultStatus(res) != PGRES_COMMAND_OK &&
+					PQresultStatus(res) != PGRES_TUPLES_OK)
+				{
+					dblink_res_error(conn, conname, res, fail,
+									 "while executing query");
+					/* if fail isn't set, we'll return an empty query result */
+				}
+				else
+				{
+					materializeResult(fcinfo, conn, res);
+				}
+			}
+		}
+	}
+	PG_FINALLY();
+	{
+		/* if needed, close the connection to the database */
+		if (freeconn)
+		{
+			PQfinish(conn);
+			ReleaseExternalFD();
+		}
+	}
+	PG_END_TRY();
+
+	return (Datum) 0;
+}
+
+/*
+ * Verify function caller can handle a tuplestore result, and set up for that.
+ *
+ * Note: if the caller returns without actually creating a tuplestore, the
+ * executor will treat the function result as an empty set.
+ */
+static void
+prepTuplestoreResult(FunctionCallInfo fcinfo)
+{
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+
+	/* check to see if query 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")));
+
+	/* let the executor know we're sending back a tuplestore */
+	rsinfo->returnMode = SFRM_Materialize;
+
+	/* caller must fill these to return a non-empty result */
+	rsinfo->setResult = NULL;
+	rsinfo->setDesc = NULL;
+}
+
+/*
+ * Copy the contents of the PGresult into a tuplestore to be returned
+ * as the result of the current function.
+ * The PGresult will be released in this function.
+ */
+static void
+materializeResult(FunctionCallInfo fcinfo, PGconn *conn, PGresult *res)
+{
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+
+	/* prepTuplestoreResult must have been called previously */
+	Assert(rsinfo->returnMode == SFRM_Materialize);
+
+	PG_TRY();
+	{
+		TupleDesc	tupdesc;
+		bool		is_sql_cmd;
+		int			ntuples;
+		int			nfields;
+
+		if (PQresultStatus(res) == PGRES_COMMAND_OK)
+		{
+			is_sql_cmd = true;
+
+			/*
+			 * need a tuple descriptor representing one TEXT column to return
+			 * the command status string as our result tuple
+			 */
+			tupdesc = CreateTemplateTupleDesc(1);
+			TupleDescInitEntry(tupdesc, (AttrNumber) 1, "status",
+							   TEXTOID, -1, 0);
+			ntuples = 1;
+			nfields = 1;
+		}
+		else
+		{
+			Assert(PQresultStatus(res) == PGRES_TUPLES_OK);
+
+			is_sql_cmd = false;
+
+			/* get a tuple descriptor for our result type */
+			switch (get_call_result_type(fcinfo, NULL, &tupdesc))
+			{
+				case TYPEFUNC_COMPOSITE:
+					/* success */
+					break;
+				case TYPEFUNC_RECORD:
+					/* failed to determine actual type of RECORD */
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("function returning record called in context "
+									"that cannot accept type record")));
+					break;
+				default:
+					/* result type isn't composite */
+					elog(ERROR, "return type must be a row type");
+					break;
+			}
+
+			/* make sure we have a persistent copy of the tupdesc */
+			tupdesc = CreateTupleDescCopy(tupdesc);
+			ntuples = PQntuples(res);
+			nfields = PQnfields(res);
+		}
+
+		/*
+		 * check result and tuple descriptor have the same number of columns
+		 */
+		if (nfields != tupdesc->natts)
+			ereport(ERROR,
+					(errcode(ERRCODE_DATATYPE_MISMATCH),
+					 errmsg("remote query result rowtype does not match "
+							"the specified FROM clause rowtype")));
+
+		if (ntuples > 0)
+		{
+			AttInMetadata *attinmeta;
+			int			nestlevel = -1;
+			Tuplestorestate *tupstore;
+			MemoryContext oldcontext;
+			int			row;
+			char	  **values;
+
+			attinmeta = TupleDescGetAttInMetadata(tupdesc);
+
+			/* Set GUCs to ensure we read GUC-sensitive data types correctly */
+			if (!is_sql_cmd)
+				nestlevel = applyRemoteGucs(conn);
+
+			oldcontext = MemoryContextSwitchTo(rsinfo->econtext->ecxt_per_query_memory);
+			tupstore = tuplestore_begin_heap(true, false, work_mem);
+			rsinfo->setResult = tupstore;
+			rsinfo->setDesc = tupdesc;
+			MemoryContextSwitchTo(oldcontext);
+
+			values = (char **) palloc(nfields * sizeof(char *));
+
+			/* put all tuples into the tuplestore */
+			for (row = 0; row < ntuples; row++)
+			{
+				HeapTuple	tuple;
+
+				if (!is_sql_cmd)
+				{
+					int			i;
+
+					for (i = 0; i < nfields; i++)
+					{
+						if (PQgetisnull(res, row, i))
+							values[i] = NULL;
+						else
+							values[i] = PQgetvalue(res, row, i);
+					}
+				}
+				else
+				{
+					values[0] = PQcmdStatus(res);
+				}
+
+				/* build the tuple and put it into the tuplestore. */
+				tuple = BuildTupleFromCStrings(attinmeta, values);
+				tuplestore_puttuple(tupstore, tuple);
+			}
+
+			/* clean up GUC settings, if we changed any */
+			restoreLocalGucs(nestlevel);
+		}
+	}
+	PG_FINALLY();
+	{
+		/* be sure to release the libpq result */
+		PQclear(res);
+	}
+	PG_END_TRY();
+}
+
+/*
+ * Execute the given SQL command and store its results into a tuplestore
+ * to be returned as the result of the current function.
+ *
+ * This is equivalent to PQexec followed by materializeResult, but we make
+ * use of libpq's single-row mode to avoid accumulating the whole result
+ * inside libpq before it gets transferred to the tuplestore.
+ */
+static void
+materializeQueryResult(FunctionCallInfo fcinfo,
+					   PGconn *conn,
+					   const char *conname,
+					   const char *sql,
+					   bool fail)
+{
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	PGresult   *volatile res = NULL;
+	volatile storeInfo sinfo = {0};
+
+	/* prepTuplestoreResult must have been called previously */
+	Assert(rsinfo->returnMode == SFRM_Materialize);
+
+	sinfo.fcinfo = fcinfo;
+
+	PG_TRY();
+	{
+		/* Create short-lived memory context for data conversions */
+		sinfo.tmpcontext = AllocSetContextCreate(CurrentMemoryContext,
+												 "dblink temporary context",
+												 ALLOCSET_DEFAULT_SIZES);
+
+		/* execute query, collecting any tuples into the tuplestore */
+		res = storeQueryResult(&sinfo, conn, sql);
+
+		if (!res ||
+			(PQresultStatus(res) != PGRES_COMMAND_OK &&
+			 PQresultStatus(res) != PGRES_TUPLES_OK))
+		{
+			/*
+			 * dblink_res_error will clear the passed PGresult, so we need
+			 * this ugly dance to avoid doing so twice during error exit
+			 */
+			PGresult   *res1 = res;
+
+			res = NULL;
+			dblink_res_error(conn, conname, res1, fail,
+							 "while executing query");
+			/* if fail isn't set, we'll return an empty query result */
+		}
+		else if (PQresultStatus(res) == PGRES_COMMAND_OK)
+		{
+			/*
+			 * storeRow didn't get called, so we need to convert the command
+			 * status string to a tuple manually
+			 */
+			TupleDesc	tupdesc;
+			AttInMetadata *attinmeta;
+			Tuplestorestate *tupstore;
+			HeapTuple	tuple;
+			char	   *values[1];
+			MemoryContext oldcontext;
+
+			/*
+			 * need a tuple descriptor representing one TEXT column to return
+			 * the command status string as our result tuple
+			 */
+			tupdesc = CreateTemplateTupleDesc(1);
+			TupleDescInitEntry(tupdesc, (AttrNumber) 1, "status",
+							   TEXTOID, -1, 0);
+			attinmeta = TupleDescGetAttInMetadata(tupdesc);
+
+			oldcontext = MemoryContextSwitchTo(rsinfo->econtext->ecxt_per_query_memory);
+			tupstore = tuplestore_begin_heap(true, false, work_mem);
+			rsinfo->setResult = tupstore;
+			rsinfo->setDesc = tupdesc;
+			MemoryContextSwitchTo(oldcontext);
+
+			values[0] = PQcmdStatus(res);
+
+			/* build the tuple and put it into the tuplestore. */
+			tuple = BuildTupleFromCStrings(attinmeta, values);
+			tuplestore_puttuple(tupstore, tuple);
+
+			PQclear(res);
+			res = NULL;
+		}
+		else
+		{
+			Assert(PQresultStatus(res) == PGRES_TUPLES_OK);
+			/* storeRow should have created a tuplestore */
+			Assert(rsinfo->setResult != NULL);
+
+			PQclear(res);
+			res = NULL;
+		}
+
+		/* clean up data conversion short-lived memory context */
+		if (sinfo.tmpcontext != NULL)
+			MemoryContextDelete(sinfo.tmpcontext);
+		sinfo.tmpcontext = NULL;
+
+		PQclear(sinfo.last_res);
+		sinfo.last_res = NULL;
+		PQclear(sinfo.cur_res);
+		sinfo.cur_res = NULL;
+	}
+	PG_CATCH();
+	{
+		/* be sure to release any libpq result we collected */
+		PQclear(res);
+		PQclear(sinfo.last_res);
+		PQclear(sinfo.cur_res);
+		/* and clear out any pending data in libpq */
+		while ((res = PQgetResult(conn)) != NULL)
+			PQclear(res);
+		PG_RE_THROW();
+	}
+	PG_END_TRY();
+}
+
+/*
+ * Execute query, and send any result rows to sinfo->tuplestore.
+ */
+static PGresult *
+storeQueryResult(volatile storeInfo *sinfo, PGconn *conn, const char *sql)
+{
+	bool		first = true;
+	int			nestlevel = -1;
+	PGresult   *res;
+
+	if (!PQsendQuery(conn, sql))
+		elog(ERROR, "could not send query: %s", pchomp(PQerrorMessage(conn)));
+
+	if (!PQsetSingleRowMode(conn))	/* shouldn't fail */
+		elog(ERROR, "failed to set single-row mode for dblink query");
+
+	for (;;)
+	{
+		CHECK_FOR_INTERRUPTS();
+
+		sinfo->cur_res = PQgetResult(conn);
+		if (!sinfo->cur_res)
+			break;
+
+		if (PQresultStatus(sinfo->cur_res) == PGRES_SINGLE_TUPLE)
+		{
+			/* got one row from possibly-bigger resultset */
+
+			/*
+			 * Set GUCs to ensure we read GUC-sensitive data types correctly.
+			 * We shouldn't do this until we have a row in hand, to ensure
+			 * libpq has seen any earlier ParameterStatus protocol messages.
+			 */
+			if (first && nestlevel < 0)
+				nestlevel = applyRemoteGucs(conn);
+
+			storeRow(sinfo, sinfo->cur_res, first);
+
+			PQclear(sinfo->cur_res);
+			sinfo->cur_res = NULL;
+			first = false;
+		}
+		else
+		{
+			/* if empty resultset, fill tuplestore header */
+			if (first && PQresultStatus(sinfo->cur_res) == PGRES_TUPLES_OK)
+				storeRow(sinfo, sinfo->cur_res, first);
+
+			/* store completed result at last_res */
+			PQclear(sinfo->last_res);
+			sinfo->last_res = sinfo->cur_res;
+			sinfo->cur_res = NULL;
+			first = true;
+		}
+	}
+
+	/* clean up GUC settings, if we changed any */
+	restoreLocalGucs(nestlevel);
+
+	/* return last_res */
+	res = sinfo->last_res;
+	sinfo->last_res = NULL;
+	return res;
+}
+
+/*
+ * Send single row to sinfo->tuplestore.
+ *
+ * If "first" is true, create the tuplestore using PGresult's metadata
+ * (in this case the PGresult might contain either zero or one row).
+ */
+static void
+storeRow(volatile storeInfo *sinfo, PGresult *res, bool first)
+{
+	int			nfields = PQnfields(res);
+	HeapTuple	tuple;
+	int			i;
+	MemoryContext oldcontext;
+
+	if (first)
+	{
+		/* Prepare for new result set */
+		ReturnSetInfo *rsinfo = (ReturnSetInfo *) sinfo->fcinfo->resultinfo;
+		TupleDesc	tupdesc;
+
+		/*
+		 * It's possible to get more than one result set if the query string
+		 * contained multiple SQL commands.  In that case, we follow PQexec's
+		 * traditional behavior of throwing away all but the last result.
+		 */
+		if (sinfo->tuplestore)
+			tuplestore_end(sinfo->tuplestore);
+		sinfo->tuplestore = NULL;
+
+		/* get a tuple descriptor for our result type */
+		switch (get_call_result_type(sinfo->fcinfo, NULL, &tupdesc))
+		{
+			case TYPEFUNC_COMPOSITE:
+				/* success */
+				break;
+			case TYPEFUNC_RECORD:
+				/* failed to determine actual type of RECORD */
+				ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						 errmsg("function returning record called in context "
+								"that cannot accept type record")));
+				break;
+			default:
+				/* result type isn't composite */
+				elog(ERROR, "return type must be a row type");
+				break;
+		}
+
+		/* make sure we have a persistent copy of the tupdesc */
+		tupdesc = CreateTupleDescCopy(tupdesc);
+
+		/* check result and tuple descriptor have the same number of columns */
+		if (nfields != tupdesc->natts)
+			ereport(ERROR,
+					(errcode(ERRCODE_DATATYPE_MISMATCH),
+					 errmsg("remote query result rowtype does not match "
+							"the specified FROM clause rowtype")));
+
+		/* Prepare attinmeta for later data conversions */
+		sinfo->attinmeta = TupleDescGetAttInMetadata(tupdesc);
+
+		/* Create a new, empty tuplestore */
+		oldcontext = MemoryContextSwitchTo(rsinfo->econtext->ecxt_per_query_memory);
+		sinfo->tuplestore = tuplestore_begin_heap(true, false, work_mem);
+		rsinfo->setResult = sinfo->tuplestore;
+		rsinfo->setDesc = tupdesc;
+		MemoryContextSwitchTo(oldcontext);
+
+		/* Done if empty resultset */
+		if (PQntuples(res) == 0)
+			return;
+
+		/*
+		 * Set up sufficiently-wide string pointers array; this won't change
+		 * in size so it's easy to preallocate.
+		 */
+		if (sinfo->cstrs)
+			pfree(sinfo->cstrs);
+		sinfo->cstrs = (char **) palloc(nfields * sizeof(char *));
+	}
+
+	/* Should have a single-row result if we get here */
+	Assert(PQntuples(res) == 1);
+
+	/*
+	 * Do the following work in a temp context that we reset after each tuple.
+	 * This cleans up not only the data we have direct access to, but any
+	 * cruft the I/O functions might leak.
+	 */
+	oldcontext = MemoryContextSwitchTo(sinfo->tmpcontext);
+
+	/*
+	 * Fill cstrs with null-terminated strings of column values.
+	 */
+	for (i = 0; i < nfields; i++)
+	{
+		if (PQgetisnull(res, 0, i))
+			sinfo->cstrs[i] = NULL;
+		else
+			sinfo->cstrs[i] = PQgetvalue(res, 0, i);
+	}
+
+	/* Convert row to a tuple, and add it to the tuplestore */
+	tuple = BuildTupleFromCStrings(sinfo->attinmeta, sinfo->cstrs);
+
+	tuplestore_puttuple(sinfo->tuplestore, tuple);
+
+	/* Clean up */
+	MemoryContextSwitchTo(oldcontext);
+	MemoryContextReset(sinfo->tmpcontext);
+}
+
+/*
+ * List all open dblink connections by name.
+ * Returns an array of all connection names.
+ * Takes no params
+ */
+PG_FUNCTION_INFO_V1(dblink_get_connections);
+Datum
+dblink_get_connections(PG_FUNCTION_ARGS)
+{
+	HASH_SEQ_STATUS status;
+	remoteConnHashEnt *hentry;
+	ArrayBuildState *astate = NULL;
+
+	if (remoteConnHash)
+	{
+		hash_seq_init(&status, remoteConnHash);
+		while ((hentry = (remoteConnHashEnt *) hash_seq_search(&status)) != NULL)
+		{
+			/* stash away current value */
+			astate = accumArrayResult(astate,
+									  CStringGetTextDatum(hentry->name),
+									  false, TEXTOID, CurrentMemoryContext);
+		}
+	}
+
+	if (astate)
+		PG_RETURN_ARRAYTYPE_P(makeArrayResult(astate,
+											  CurrentMemoryContext));
+	else
+		PG_RETURN_NULL();
+}
+
+/*
+ * Checks if a given remote connection is busy
+ *
+ * Returns 1 if the connection is busy, 0 otherwise
+ * Params:
+ *	text connection_name - name of the connection to check
+ *
+ */
+PG_FUNCTION_INFO_V1(dblink_is_busy);
+Datum
+dblink_is_busy(PG_FUNCTION_ARGS)
+{
+	PGconn	   *conn;
+
+	dblink_init();
+	conn = dblink_get_named_conn(text_to_cstring(PG_GETARG_TEXT_PP(0)));
+
+	PQconsumeInput(conn);
+	PG_RETURN_INT32(PQisBusy(conn));
+}
+
+/*
+ * Cancels a running request on a connection
+ *
+ * Returns text:
+ *	"OK" if the cancel request has been sent correctly,
+ *		an error message otherwise
+ *
+ * Params:
+ *	text connection_name - name of the connection to check
+ *
+ */
+PG_FUNCTION_INFO_V1(dblink_cancel_query);
+Datum
+dblink_cancel_query(PG_FUNCTION_ARGS)
+{
+	int			res;
+	PGconn	   *conn;
+	PGcancel   *cancel;
+	char		errbuf[256];
+
+	dblink_init();
+	conn = dblink_get_named_conn(text_to_cstring(PG_GETARG_TEXT_PP(0)));
+	cancel = PQgetCancel(conn);
+
+	res = PQcancel(cancel, errbuf, 256);
+	PQfreeCancel(cancel);
+
+	if (res == 1)
+		PG_RETURN_TEXT_P(cstring_to_text("OK"));
+	else
+		PG_RETURN_TEXT_P(cstring_to_text(errbuf));
+}
+
+
+/*
+ * Get error message from a connection
+ *
+ * Returns text:
+ *	"OK" if no error, an error message otherwise
+ *
+ * Params:
+ *	text connection_name - name of the connection to check
+ *
+ */
+PG_FUNCTION_INFO_V1(dblink_error_message);
+Datum
+dblink_error_message(PG_FUNCTION_ARGS)
+{
+	char	   *msg;
+	PGconn	   *conn;
+
+	dblink_init();
+	conn = dblink_get_named_conn(text_to_cstring(PG_GETARG_TEXT_PP(0)));
+
+	msg = PQerrorMessage(conn);
+	if (msg == NULL || msg[0] == '\0')
+		PG_RETURN_TEXT_P(cstring_to_text("OK"));
+	else
+		PG_RETURN_TEXT_P(cstring_to_text(pchomp(msg)));
+}
+
+/*
+ * Execute an SQL non-SELECT command
+ */
+PG_FUNCTION_INFO_V1(dblink_exec);
+Datum
+dblink_exec(PG_FUNCTION_ARGS)
+{
+	text	   *volatile sql_cmd_status = NULL;
+	PGconn	   *volatile conn = NULL;
+	volatile bool freeconn = false;
+
+	dblink_init();
+
+	PG_TRY();
+	{
+		PGresult   *res = NULL;
+		char	   *sql = NULL;
+		char	   *conname = NULL;
+		bool		fail = true;	/* default to backward compatible behavior */
+
+		if (PG_NARGS() == 3)
+		{
+			/* must be text,text,bool */
+			conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+			sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
+			fail = PG_GETARG_BOOL(2);
+			dblink_get_conn(conname, &conn, &conname, &freeconn);
+		}
+		else if (PG_NARGS() == 2)
+		{
+			/* might be text,text or text,bool */
+			if (get_fn_expr_argtype(fcinfo->flinfo, 1) == BOOLOID)
+			{
+				sql = text_to_cstring(PG_GETARG_TEXT_PP(0));
+				fail = PG_GETARG_BOOL(1);
+				conn = pconn->conn;
+			}
+			else
+			{
+				conname = text_to_cstring(PG_GETARG_TEXT_PP(0));
+				sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
+				dblink_get_conn(conname, &conn, &conname, &freeconn);
+			}
+		}
+		else if (PG_NARGS() == 1)
+		{
+			/* must be single text argument */
+			conn = pconn->conn;
+			sql = text_to_cstring(PG_GETARG_TEXT_PP(0));
+		}
+		else
+			/* shouldn't happen */
+			elog(ERROR, "wrong number of arguments");
+
+		if (!conn)
+			dblink_conn_not_avail(conname);
+
+		res = PQexec(conn, sql);
+		if (!res ||
+			(PQresultStatus(res) != PGRES_COMMAND_OK &&
+			 PQresultStatus(res) != PGRES_TUPLES_OK))
+		{
+			dblink_res_error(conn, conname, res, fail,
+							 "while executing command");
+
+			/*
+			 * and save a copy of the command status string to return as our
+			 * result tuple
+			 */
+			sql_cmd_status = cstring_to_text("ERROR");
+		}
+		else if (PQresultStatus(res) == PGRES_COMMAND_OK)
+		{
+			/*
+			 * and save a copy of the command status string to return as our
+			 * result tuple
+			 */
+			sql_cmd_status = cstring_to_text(PQcmdStatus(res));
+			PQclear(res);
+		}
+		else
+		{
+			PQclear(res);
+			ereport(ERROR,
+					(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
+					 errmsg("statement returning results not allowed")));
+		}
+	}
+	PG_FINALLY();
+	{
+		/* if needed, close the connection to the database */
+		if (freeconn)
+		{
+			PQfinish(conn);
+			ReleaseExternalFD();
+		}
+	}
+	PG_END_TRY();
+
+	PG_RETURN_TEXT_P(sql_cmd_status);
+}
+
+
+/*
+ * dblink_get_pkey
+ *
+ * Return list of primary key fields for the supplied relation,
+ * or NULL if none exists.
+ */
+PG_FUNCTION_INFO_V1(dblink_get_pkey);
+Datum
+dblink_get_pkey(PG_FUNCTION_ARGS)
+{
+	int16		indnkeyatts;
+	char	  **results;
+	FuncCallContext *funcctx;
+	int32		call_cntr;
+	int32		max_calls;
+	AttInMetadata *attinmeta;
+	MemoryContext oldcontext;
+
+	/* stuff done only on the first call of the function */
+	if (SRF_IS_FIRSTCALL())
+	{
+		Relation	rel;
+		TupleDesc	tupdesc;
+
+		/* create a function context for cross-call persistence */
+		funcctx = SRF_FIRSTCALL_INIT();
+
+		/*
+		 * switch to memory context appropriate for multiple function calls
+		 */
+		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
+
+		/* open target relation */
+		rel = get_rel_from_relname(PG_GETARG_TEXT_PP(0), AccessShareLock, ACL_SELECT);
+
+		/* get the array of attnums */
+		results = get_pkey_attnames(rel, &indnkeyatts);
+
+		relation_close(rel, AccessShareLock);
+
+		/*
+		 * need a tuple descriptor representing one INT and one TEXT column
+		 */
+		tupdesc = CreateTemplateTupleDesc(2);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 1, "position",
+						   INT4OID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 2, "colname",
+						   TEXTOID, -1, 0);
+
+		/*
+		 * Generate attribute metadata needed later to produce tuples from raw
+		 * C strings
+		 */
+		attinmeta = TupleDescGetAttInMetadata(tupdesc);
+		funcctx->attinmeta = attinmeta;
+
+		if ((results != NULL) && (indnkeyatts > 0))
+		{
+			funcctx->max_calls = indnkeyatts;
+
+			/* got results, keep track of them */
+			funcctx->user_fctx = results;
+		}
+		else
+		{
+			/* fast track when no results */
+			MemoryContextSwitchTo(oldcontext);
+			SRF_RETURN_DONE(funcctx);
+		}
+
+		MemoryContextSwitchTo(oldcontext);
+	}
+
+	/* stuff done on every call of the function */
+	funcctx = SRF_PERCALL_SETUP();
+
+	/*
+	 * initialize per-call variables
+	 */
+	call_cntr = funcctx->call_cntr;
+	max_calls = funcctx->max_calls;
+
+	results = (char **) funcctx->user_fctx;
+	attinmeta = funcctx->attinmeta;
+
+	if (call_cntr < max_calls)	/* do when there is more left to send */
+	{
+		char	  **values;
+		HeapTuple	tuple;
+		Datum		result;
+
+		values = (char **) palloc(2 * sizeof(char *));
+		values[0] = psprintf("%d", call_cntr + 1);
+		values[1] = results[call_cntr];
+
+		/* build the tuple */
+		tuple = BuildTupleFromCStrings(attinmeta, values);
+
+		/* make the tuple into a datum */
+		result = HeapTupleGetDatum(tuple);
+
+		SRF_RETURN_NEXT(funcctx, result);
+	}
+	else
+	{
+		/* do when there is no more left */
+		SRF_RETURN_DONE(funcctx);
+	}
+}
+
+
+/*
+ * dblink_build_sql_insert
+ *
+ * Used to generate an SQL insert statement
+ * based on an existing tuple in a local relation.
+ * This is useful for selectively replicating data
+ * to another server via dblink.
+ *
+ * API:
+ * <relname> - name of local table of interest
+ * <pkattnums> - an int2vector of attnums which will be used
+ * to identify the local tuple of interest
+ * <pknumatts> - number of attnums in pkattnums
+ * <src_pkattvals_arry> - text array of key values which will be used
+ * to identify the local tuple of interest
+ * <tgt_pkattvals_arry> - text array of key values which will be used
+ * to build the string for execution remotely. These are substituted
+ * for their counterparts in src_pkattvals_arry
+ */
+PG_FUNCTION_INFO_V1(dblink_build_sql_insert);
+Datum
+dblink_build_sql_insert(PG_FUNCTION_ARGS)
+{
+	text	   *relname_text = PG_GETARG_TEXT_PP(0);
+	int2vector *pkattnums_arg = (int2vector *) PG_GETARG_POINTER(1);
+	int32		pknumatts_arg = PG_GETARG_INT32(2);
+	ArrayType  *src_pkattvals_arry = PG_GETARG_ARRAYTYPE_P(3);
+	ArrayType  *tgt_pkattvals_arry = PG_GETARG_ARRAYTYPE_P(4);
+	Relation	rel;
+	int		   *pkattnums;
+	int			pknumatts;
+	char	  **src_pkattvals;
+	char	  **tgt_pkattvals;
+	int			src_nitems;
+	int			tgt_nitems;
+	char	   *sql;
+
+	/*
+	 * Open target relation.
+	 */
+	rel = get_rel_from_relname(relname_text, AccessShareLock, ACL_SELECT);
+
+	/*
+	 * Process pkattnums argument.
+	 */
+	validate_pkattnums(rel, pkattnums_arg, pknumatts_arg,
+					   &pkattnums, &pknumatts);
+
+	/*
+	 * Source array is made up of key values that will be used to locate the
+	 * tuple of interest from the local system.
+	 */
+	src_pkattvals = get_text_array_contents(src_pkattvals_arry, &src_nitems);
+
+	/*
+	 * There should be one source array key value for each key attnum
+	 */
+	if (src_nitems != pknumatts)
+		ereport(ERROR,
+				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
+				 errmsg("source key array length must match number of key attributes")));
+
+	/*
+	 * Target array is made up of key values that will be used to build the
+	 * SQL string for use on the remote system.
+	 */
+	tgt_pkattvals = get_text_array_contents(tgt_pkattvals_arry, &tgt_nitems);
+
+	/*
+	 * There should be one target array key value for each key attnum
+	 */
+	if (tgt_nitems != pknumatts)
+		ereport(ERROR,
+				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
+				 errmsg("target key array length must match number of key attributes")));
+
+	/*
+	 * Prep work is finally done. Go get the SQL string.
+	 */
+	sql = get_sql_insert(rel, pkattnums, pknumatts, src_pkattvals, tgt_pkattvals);
+
+	/*
+	 * Now we can close the relation.
+	 */
+	relation_close(rel, AccessShareLock);
+
+	/*
+	 * And send it
+	 */
+	PG_RETURN_TEXT_P(cstring_to_text(sql));
+}
+
+
+/*
+ * dblink_build_sql_delete
+ *
+ * Used to generate an SQL delete statement.
+ * This is useful for selectively replicating a
+ * delete to another server via dblink.
+ *
+ * API:
+ * <relname> - name of remote table of interest
+ * <pkattnums> - an int2vector of attnums which will be used
+ * to identify the remote tuple of interest
+ * <pknumatts> - number of attnums in pkattnums
+ * <tgt_pkattvals_arry> - text array of key values which will be used
+ * to build the string for execution remotely.
+ */
+PG_FUNCTION_INFO_V1(dblink_build_sql_delete);
+Datum
+dblink_build_sql_delete(PG_FUNCTION_ARGS)
+{
+	text	   *relname_text = PG_GETARG_TEXT_PP(0);
+	int2vector *pkattnums_arg = (int2vector *) PG_GETARG_POINTER(1);
+	int32		pknumatts_arg = PG_GETARG_INT32(2);
+	ArrayType  *tgt_pkattvals_arry = PG_GETARG_ARRAYTYPE_P(3);
+	Relation	rel;
+	int		   *pkattnums;
+	int			pknumatts;
+	char	  **tgt_pkattvals;
+	int			tgt_nitems;
+	char	   *sql;
+
+	/*
+	 * Open target relation.
+	 */
+	rel = get_rel_from_relname(relname_text, AccessShareLock, ACL_SELECT);
+
+	/*
+	 * Process pkattnums argument.
+	 */
+	validate_pkattnums(rel, pkattnums_arg, pknumatts_arg,
+					   &pkattnums, &pknumatts);
+
+	/*
+	 * Target array is made up of key values that will be used to build the
+	 * SQL string for use on the remote system.
+	 */
+	tgt_pkattvals = get_text_array_contents(tgt_pkattvals_arry, &tgt_nitems);
+
+	/*
+	 * There should be one target array key value for each key attnum
+	 */
+	if (tgt_nitems != pknumatts)
+		ereport(ERROR,
+				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
+				 errmsg("target key array length must match number of key attributes")));
+
+	/*
+	 * Prep work is finally done. Go get the SQL string.
+	 */
+	sql = get_sql_delete(rel, pkattnums, pknumatts, tgt_pkattvals);
+
+	/*
+	 * Now we can close the relation.
+	 */
+	relation_close(rel, AccessShareLock);
+
+	/*
+	 * And send it
+	 */
+	PG_RETURN_TEXT_P(cstring_to_text(sql));
+}
+
+
+/*
+ * dblink_build_sql_update
+ *
+ * Used to generate an SQL update statement
+ * based on an existing tuple in a local relation.
+ * This is useful for selectively replicating data
+ * to another server via dblink.
+ *
+ * API:
+ * <relname> - name of local table of interest
+ * <pkattnums> - an int2vector of attnums which will be used
+ * to identify the local tuple of interest
+ * <pknumatts> - number of attnums in pkattnums
+ * <src_pkattvals_arry> - text array of key values which will be used
+ * to identify the local tuple of interest
+ * <tgt_pkattvals_arry> - text array of key values which will be used
+ * to build the string for execution remotely. These are substituted
+ * for their counterparts in src_pkattvals_arry
+ */
+PG_FUNCTION_INFO_V1(dblink_build_sql_update);
+Datum
+dblink_build_sql_update(PG_FUNCTION_ARGS)
+{
+	text	   *relname_text = PG_GETARG_TEXT_PP(0);
+	int2vector *pkattnums_arg = (int2vector *) PG_GETARG_POINTER(1);
+	int32		pknumatts_arg = PG_GETARG_INT32(2);
+	ArrayType  *src_pkattvals_arry = PG_GETARG_ARRAYTYPE_P(3);
+	ArrayType  *tgt_pkattvals_arry = PG_GETARG_ARRAYTYPE_P(4);
+	Relation	rel;
+	int		   *pkattnums;
+	int			pknumatts;
+	char	  **src_pkattvals;
+	char	  **tgt_pkattvals;
+	int			src_nitems;
+	int			tgt_nitems;
+	char	   *sql;
+
+	/*
+	 * Open target relation.
+	 */
+	rel = get_rel_from_relname(relname_text, AccessShareLock, ACL_SELECT);
+
+	/*
+	 * Process pkattnums argument.
+	 */
+	validate_pkattnums(rel, pkattnums_arg, pknumatts_arg,
+					   &pkattnums, &pknumatts);
+
+	/*
+	 * Source array is made up of key values that will be used to locate the
+	 * tuple of interest from the local system.
+	 */
+	src_pkattvals = get_text_array_contents(src_pkattvals_arry, &src_nitems);
+
+	/*
+	 * There should be one source array key value for each key attnum
+	 */
+	if (src_nitems != pknumatts)
+		ereport(ERROR,
+				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
+				 errmsg("source key array length must match number of key attributes")));
+
+	/*
+	 * Target array is made up of key values that will be used to build the
+	 * SQL string for use on the remote system.
+	 */
+	tgt_pkattvals = get_text_array_contents(tgt_pkattvals_arry, &tgt_nitems);
+
+	/*
+	 * There should be one target array key value for each key attnum
+	 */
+	if (tgt_nitems != pknumatts)
+		ereport(ERROR,
+				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
+				 errmsg("target key array length must match number of key attributes")));
+
+	/*
+	 * Prep work is finally done. Go get the SQL string.
+	 */
+	sql = get_sql_update(rel, pkattnums, pknumatts, src_pkattvals, tgt_pkattvals);
+
+	/*
+	 * Now we can close the relation.
+	 */
+	relation_close(rel, AccessShareLock);
+
+	/*
+	 * And send it
+	 */
+	PG_RETURN_TEXT_P(cstring_to_text(sql));
+}
+
+/*
+ * dblink_current_query
+ * return the current query string
+ * to allow its use in (among other things)
+ * rewrite rules
+ */
+PG_FUNCTION_INFO_V1(dblink_current_query);
+Datum
+dblink_current_query(PG_FUNCTION_ARGS)
+{
+	/* This is now just an alias for the built-in function current_query() */
+	PG_RETURN_DATUM(current_query(fcinfo));
+}
+
+/*
+ * Retrieve async notifications for a connection.
+ *
+ * Returns a setof record of notifications, or an empty set if none received.
+ * Can optionally take a named connection as parameter, but uses the unnamed
+ * connection per default.
+ *
+ */
+#define DBLINK_NOTIFY_COLS		3
+
+PG_FUNCTION_INFO_V1(dblink_get_notify);
+Datum
+dblink_get_notify(PG_FUNCTION_ARGS)
+{
+	PGconn	   *conn;
+	PGnotify   *notify;
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+
+	dblink_init();
+	if (PG_NARGS() == 1)
+		conn = dblink_get_named_conn(text_to_cstring(PG_GETARG_TEXT_PP(0)));
+	else
+		conn = pconn->conn;
+
+	InitMaterializedSRF(fcinfo, 0);
+
+	PQconsumeInput(conn);
+	while ((notify = PQnotifies(conn)) != NULL)
+	{
+		Datum		values[DBLINK_NOTIFY_COLS];
+		bool		nulls[DBLINK_NOTIFY_COLS];
+
+		memset(values, 0, sizeof(values));
+		memset(nulls, 0, sizeof(nulls));
+
+		if (notify->relname != NULL)
+			values[0] = CStringGetTextDatum(notify->relname);
+		else
+			nulls[0] = true;
+
+		values[1] = Int32GetDatum(notify->be_pid);
+
+		if (notify->extra != NULL)
+			values[2] = CStringGetTextDatum(notify->extra);
+		else
+			nulls[2] = true;
+
+		tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
+
+		PQfreemem(notify);
+		PQconsumeInput(conn);
+	}
+
+	return (Datum) 0;
+}
+
+/*
+ * Validate the options given to a dblink foreign server or user mapping.
+ * Raise an error if any option is invalid.
+ *
+ * We just check the names of options here, so semantic errors in options,
+ * such as invalid numeric format, will be detected at the attempt to connect.
+ */
+PG_FUNCTION_INFO_V1(dblink_fdw_validator);
+Datum
+dblink_fdw_validator(PG_FUNCTION_ARGS)
+{
+	List	   *options_list = untransformRelOptions(PG_GETARG_DATUM(0));
+	Oid			context = PG_GETARG_OID(1);
+	ListCell   *cell;
+
+	static const PQconninfoOption *options = NULL;
+
+	/*
+	 * Get list of valid libpq options.
+	 *
+	 * To avoid unnecessary work, we get the list once and use it throughout
+	 * the lifetime of this backend process.  We don't need to care about
+	 * memory context issues, because PQconndefaults allocates with malloc.
+	 */
+	if (!options)
+	{
+		options = PQconndefaults();
+		if (!options)			/* assume reason for failure is OOM */
+			ereport(ERROR,
+					(errcode(ERRCODE_FDW_OUT_OF_MEMORY),
+					 errmsg("out of memory"),
+					 errdetail("Could not get libpq's default connection options.")));
+	}
+
+	/* Validate each supplied option. */
+	foreach(cell, options_list)
+	{
+		DefElem    *def = (DefElem *) lfirst(cell);
+
+		if (!is_valid_dblink_option(options, def->defname, context))
+		{
+			/*
+			 * Unknown option, or invalid option for the context specified, so
+			 * complain about it.  Provide a hint with list of valid options
+			 * for the context.
+			 */
+			StringInfoData buf;
+			const PQconninfoOption *opt;
+
+			initStringInfo(&buf);
+			for (opt = options; opt->keyword; opt++)
+			{
+				if (is_valid_dblink_option(options, opt->keyword, context))
+					appendStringInfo(&buf, "%s%s",
+									 (buf.len > 0) ? ", " : "",
+									 opt->keyword);
+			}
+			ereport(ERROR,
+					(errcode(ERRCODE_FDW_OPTION_NAME_NOT_FOUND),
+					 errmsg("invalid option \"%s\"", def->defname),
+					 buf.len > 0
+					 ? errhint("Valid options in this context are: %s",
+							   buf.data)
+					 : errhint("There are no valid options in this context.")));
+		}
+	}
+
+	PG_RETURN_VOID();
+}
+
+
+/*************************************************************
+ * internal functions
+ */
+
+
+/*
+ * get_pkey_attnames
+ *
+ * Get the primary key attnames for the given relation.
+ * Return NULL, and set indnkeyatts = 0, if no primary key exists.
+ */
+static char **
+get_pkey_attnames(Relation rel, int16 *indnkeyatts)
+{
+	Relation	indexRelation;
+	ScanKeyData skey;
+	SysScanDesc scan;
+	HeapTuple	indexTuple;
+	int			i;
+	char	  **result = NULL;
+	TupleDesc	tupdesc;
+
+	/* initialize indnkeyatts to 0 in case no primary key exists */
+	*indnkeyatts = 0;
+
+	tupdesc = rel->rd_att;
+
+	/* Prepare to scan pg_index for entries having indrelid = this rel. */
+	indexRelation = table_open(IndexRelationId, AccessShareLock);
+	ScanKeyInit(&skey,
+				Anum_pg_index_indrelid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(RelationGetRelid(rel)));
+
+	scan = systable_beginscan(indexRelation, IndexIndrelidIndexId, true,
+							  NULL, 1, &skey);
+
+	while (HeapTupleIsValid(indexTuple = systable_getnext(scan)))
+	{
+		Form_pg_index index = (Form_pg_index) GETSTRUCT(indexTuple);
+
+		/* we're only interested if it is the primary key */
+		if (index->indisprimary)
+		{
+			*indnkeyatts = index->indnkeyatts;
+			if (*indnkeyatts > 0)
+			{
+				result = (char **) palloc(*indnkeyatts * sizeof(char *));
+
+				for (i = 0; i < *indnkeyatts; i++)
+					result[i] = SPI_fname(tupdesc, index->indkey.values[i]);
+			}
+			break;
+		}
+	}
+
+	systable_endscan(scan);
+	table_close(indexRelation, AccessShareLock);
+
+	return result;
+}
+
+/*
+ * Deconstruct a text[] into C-strings (note any NULL elements will be
+ * returned as NULL pointers)
+ */
+static char **
+get_text_array_contents(ArrayType *array, int *numitems)
+{
+	int			ndim = ARR_NDIM(array);
+	int		   *dims = ARR_DIMS(array);
+	int			nitems;
+	int16		typlen;
+	bool		typbyval;
+	char		typalign;
+	char	  **values;
+	char	   *ptr;
+	bits8	   *bitmap;
+	int			bitmask;
+	int			i;
+
+	Assert(ARR_ELEMTYPE(array) == TEXTOID);
+
+	*numitems = nitems = ArrayGetNItems(ndim, dims);
+
+	get_typlenbyvalalign(ARR_ELEMTYPE(array),
+						 &typlen, &typbyval, &typalign);
+
+	values = (char **) palloc(nitems * sizeof(char *));
+
+	ptr = ARR_DATA_PTR(array);
+	bitmap = ARR_NULLBITMAP(array);
+	bitmask = 1;
+
+	for (i = 0; i < nitems; i++)
+	{
+		if (bitmap && (*bitmap & bitmask) == 0)
+		{
+			values[i] = NULL;
+		}
+		else
+		{
+			values[i] = TextDatumGetCString(PointerGetDatum(ptr));
+			ptr = att_addlength_pointer(ptr, typlen, ptr);
+			ptr = (char *) att_align_nominal(ptr, typalign);
+		}
+
+		/* advance bitmap pointer if any */
+		if (bitmap)
+		{
+			bitmask <<= 1;
+			if (bitmask == 0x100)
+			{
+				bitmap++;
+				bitmask = 1;
+			}
+		}
+	}
+
+	return values;
+}
+
+static char *
+get_sql_insert(Relation rel, int *pkattnums, int pknumatts, char **src_pkattvals, char **tgt_pkattvals)
+{
+	char	   *relname;
+	HeapTuple	tuple;
+	TupleDesc	tupdesc;
+	int			natts;
+	StringInfoData buf;
+	char	   *val;
+	int			key;
+	int			i;
+	bool		needComma;
+
+	initStringInfo(&buf);
+
+	/* get relation name including any needed schema prefix and quoting */
+	relname = generate_relation_name(rel);
+
+	tupdesc = rel->rd_att;
+	natts = tupdesc->natts;
+
+	tuple = get_tuple_of_interest(rel, pkattnums, pknumatts, src_pkattvals);
+	if (!tuple)
+		ereport(ERROR,
+				(errcode(ERRCODE_CARDINALITY_VIOLATION),
+				 errmsg("source row not found")));
+
+	appendStringInfo(&buf, "INSERT INTO %s(", relname);
+
+	needComma = false;
+	for (i = 0; i < natts; i++)
+	{
+		Form_pg_attribute att = TupleDescAttr(tupdesc, i);
+
+		if (att->attisdropped)
+			continue;
+
+		if (needComma)
+			appendStringInfoChar(&buf, ',');
+
+		appendStringInfoString(&buf,
+							   quote_ident_cstr(NameStr(att->attname)));
+		needComma = true;
+	}
+
+	appendStringInfoString(&buf, ") VALUES(");
+
+	/*
+	 * Note: i is physical column number (counting from 0).
+	 */
+	needComma = false;
+	for (i = 0; i < natts; i++)
+	{
+		if (TupleDescAttr(tupdesc, i)->attisdropped)
+			continue;
+
+		if (needComma)
+			appendStringInfoChar(&buf, ',');
+
+		key = get_attnum_pk_pos(pkattnums, pknumatts, i);
+
+		if (key >= 0)
+			val = tgt_pkattvals[key] ? pstrdup(tgt_pkattvals[key]) : NULL;
+		else
+			val = SPI_getvalue(tuple, tupdesc, i + 1);
+
+		if (val != NULL)
+		{
+			appendStringInfoString(&buf, quote_literal_cstr(val));
+			pfree(val);
+		}
+		else
+			appendStringInfoString(&buf, "NULL");
+		needComma = true;
+	}
+	appendStringInfoChar(&buf, ')');
+
+	return buf.data;
+}
+
+static char *
+get_sql_delete(Relation rel, int *pkattnums, int pknumatts, char **tgt_pkattvals)
+{
+	char	   *relname;
+	TupleDesc	tupdesc;
+	StringInfoData buf;
+	int			i;
+
+	initStringInfo(&buf);
+
+	/* get relation name including any needed schema prefix and quoting */
+	relname = generate_relation_name(rel);
+
+	tupdesc = rel->rd_att;
+
+	appendStringInfo(&buf, "DELETE FROM %s WHERE ", relname);
+	for (i = 0; i < pknumatts; i++)
+	{
+		int			pkattnum = pkattnums[i];
+		Form_pg_attribute attr = TupleDescAttr(tupdesc, pkattnum);
+
+		if (i > 0)
+			appendStringInfoString(&buf, " AND ");
+
+		appendStringInfoString(&buf,
+							   quote_ident_cstr(NameStr(attr->attname)));
+
+		if (tgt_pkattvals[i] != NULL)
+			appendStringInfo(&buf, " = %s",
+							 quote_literal_cstr(tgt_pkattvals[i]));
+		else
+			appendStringInfoString(&buf, " IS NULL");
+	}
+
+	return buf.data;
+}
+
+static char *
+get_sql_update(Relation rel, int *pkattnums, int pknumatts, char **src_pkattvals, char **tgt_pkattvals)
+{
+	char	   *relname;
+	HeapTuple	tuple;
+	TupleDesc	tupdesc;
+	int			natts;
+	StringInfoData buf;
+	char	   *val;
+	int			key;
+	int			i;
+	bool		needComma;
+
+	initStringInfo(&buf);
+
+	/* get relation name including any needed schema prefix and quoting */
+	relname = generate_relation_name(rel);
+
+	tupdesc = rel->rd_att;
+	natts = tupdesc->natts;
+
+	tuple = get_tuple_of_interest(rel, pkattnums, pknumatts, src_pkattvals);
+	if (!tuple)
+		ereport(ERROR,
+				(errcode(ERRCODE_CARDINALITY_VIOLATION),
+				 errmsg("source row not found")));
+
+	appendStringInfo(&buf, "UPDATE %s SET ", relname);
+
+	/*
+	 * Note: i is physical column number (counting from 0).
+	 */
+	needComma = false;
+	for (i = 0; i < natts; i++)
+	{
+		Form_pg_attribute attr = TupleDescAttr(tupdesc, i);
+
+		if (attr->attisdropped)
+			continue;
+
+		if (needComma)
+			appendStringInfoString(&buf, ", ");
+
+		appendStringInfo(&buf, "%s = ",
+						 quote_ident_cstr(NameStr(attr->attname)));
+
+		key = get_attnum_pk_pos(pkattnums, pknumatts, i);
+
+		if (key >= 0)
+			val = tgt_pkattvals[key] ? pstrdup(tgt_pkattvals[key]) : NULL;
+		else
+			val = SPI_getvalue(tuple, tupdesc, i + 1);
+
+		if (val != NULL)
+		{
+			appendStringInfoString(&buf, quote_literal_cstr(val));
+			pfree(val);
+		}
+		else
+			appendStringInfoString(&buf, "NULL");
+		needComma = true;
+	}
+
+	appendStringInfoString(&buf, " WHERE ");
+
+	for (i = 0; i < pknumatts; i++)
+	{
+		int			pkattnum = pkattnums[i];
+		Form_pg_attribute attr = TupleDescAttr(tupdesc, pkattnum);
+
+		if (i > 0)
+			appendStringInfoString(&buf, " AND ");
+
+		appendStringInfoString(&buf,
+							   quote_ident_cstr(NameStr(attr->attname)));
+
+		val = tgt_pkattvals[i];
+
+		if (val != NULL)
+			appendStringInfo(&buf, " = %s", quote_literal_cstr(val));
+		else
+			appendStringInfoString(&buf, " IS NULL");
+	}
+
+	return buf.data;
+}
+
+/*
+ * Return a properly quoted identifier.
+ * Uses quote_ident in quote.c
+ */
+static char *
+quote_ident_cstr(char *rawstr)
+{
+	text	   *rawstr_text;
+	text	   *result_text;
+	char	   *result;
+
+	rawstr_text = cstring_to_text(rawstr);
+	result_text = DatumGetTextPP(DirectFunctionCall1(quote_ident,
+													 PointerGetDatum(rawstr_text)));
+	result = text_to_cstring(result_text);
+
+	return result;
+}
+
+static int
+get_attnum_pk_pos(int *pkattnums, int pknumatts, int key)
+{
+	int			i;
+
+	/*
+	 * Not likely a long list anyway, so just scan for the value
+	 */
+	for (i = 0; i < pknumatts; i++)
+		if (key == pkattnums[i])
+			return i;
+
+	return -1;
+}
+
+static HeapTuple
+get_tuple_of_interest(Relation rel, int *pkattnums, int pknumatts, char **src_pkattvals)
+{
+	char	   *relname;
+	TupleDesc	tupdesc;
+	int			natts;
+	StringInfoData buf;
+	int			ret;
+	HeapTuple	tuple;
+	int			i;
+
+	/*
+	 * Connect to SPI manager
+	 */
+	if ((ret = SPI_connect()) < 0)
+		/* internal error */
+		elog(ERROR, "SPI connect failure - returned %d", ret);
+
+	initStringInfo(&buf);
+
+	/* get relation name including any needed schema prefix and quoting */
+	relname = generate_relation_name(rel);
+
+	tupdesc = rel->rd_att;
+	natts = tupdesc->natts;
+
+	/*
+	 * Build sql statement to look up tuple of interest, ie, the one matching
+	 * src_pkattvals.  We used to use "SELECT *" here, but it's simpler to
+	 * generate a result tuple that matches the table's physical structure,
+	 * with NULLs for any dropped columns.  Otherwise we have to deal with two
+	 * different tupdescs and everything's very confusing.
+	 */
+	appendStringInfoString(&buf, "SELECT ");
+
+	for (i = 0; i < natts; i++)
+	{
+		Form_pg_attribute attr = TupleDescAttr(tupdesc, i);
+
+		if (i > 0)
+			appendStringInfoString(&buf, ", ");
+
+		if (attr->attisdropped)
+			appendStringInfoString(&buf, "NULL");
+		else
+			appendStringInfoString(&buf,
+								   quote_ident_cstr(NameStr(attr->attname)));
+	}
+
+	appendStringInfo(&buf, " FROM %s WHERE ", relname);
+
+	for (i = 0; i < pknumatts; i++)
+	{
+		int			pkattnum = pkattnums[i];
+		Form_pg_attribute attr = TupleDescAttr(tupdesc, pkattnum);
+
+		if (i > 0)
+			appendStringInfoString(&buf, " AND ");
+
+		appendStringInfoString(&buf,
+							   quote_ident_cstr(NameStr(attr->attname)));
+
+		if (src_pkattvals[i] != NULL)
+			appendStringInfo(&buf, " = %s",
+							 quote_literal_cstr(src_pkattvals[i]));
+		else
+			appendStringInfoString(&buf, " IS NULL");
+	}
+
+	/*
+	 * Retrieve the desired tuple
+	 */
+	ret = SPI_exec(buf.data, 0);
+	pfree(buf.data);
+
+	/*
+	 * Only allow one qualifying tuple
+	 */
+	if ((ret == SPI_OK_SELECT) && (SPI_processed > 1))
+		ereport(ERROR,
+				(errcode(ERRCODE_CARDINALITY_VIOLATION),
+				 errmsg("source criteria matched more than one record")));
+
+	else if (ret == SPI_OK_SELECT && SPI_processed == 1)
+	{
+		SPITupleTable *tuptable = SPI_tuptable;
+
+		tuple = SPI_copytuple(tuptable->vals[0]);
+		SPI_finish();
+
+		return tuple;
+	}
+	else
+	{
+		/*
+		 * no qualifying tuples
+		 */
+		SPI_finish();
+
+		return NULL;
+	}
+
+	/*
+	 * never reached, but keep compiler quiet
+	 */
+	return NULL;
+}
+
+/*
+ * Open the relation named by relname_text, acquire specified type of lock,
+ * verify we have specified permissions.
+ * Caller must close rel when done with it.
+ */
+static Relation
+get_rel_from_relname(text *relname_text, LOCKMODE lockmode, AclMode aclmode)
+{
+	RangeVar   *relvar;
+	Relation	rel;
+	AclResult	aclresult;
+
+	relvar = makeRangeVarFromNameList(textToQualifiedNameList(relname_text));
+	rel = table_openrv(relvar, lockmode);
+
+	aclresult = pg_class_aclcheck(RelationGetRelid(rel), GetUserId(),
+								  aclmode);
+	if (aclresult != ACLCHECK_OK)
+		aclcheck_error(aclresult, get_relkind_objtype(rel->rd_rel->relkind),
+					   RelationGetRelationName(rel));
+
+	return rel;
+}
+
+/*
+ * generate_relation_name - copied from ruleutils.c
+ *		Compute the name to display for a relation
+ *
+ * The result includes all necessary quoting and schema-prefixing.
+ */
+static char *
+generate_relation_name(Relation rel)
+{
+	char	   *nspname;
+	char	   *result;
+
+	/* Qualify the name if not visible in search path */
+	if (RelationIsVisible(RelationGetRelid(rel)))
+		nspname = NULL;
+	else
+		nspname = get_namespace_name(rel->rd_rel->relnamespace);
+
+	result = quote_qualified_identifier(nspname, RelationGetRelationName(rel));
+
+	return result;
+}
+
+
+static remoteConn *
+getConnectionByName(const char *name)
+{
+	remoteConnHashEnt *hentry;
+	char	   *key;
+
+	if (!remoteConnHash)
+		remoteConnHash = createConnHash();
+
+	key = pstrdup(name);
+	truncate_identifier(key, strlen(key), false);
+	hentry = (remoteConnHashEnt *) hash_search(remoteConnHash,
+											   key, HASH_FIND, NULL);
+
+	if (hentry)
+		return hentry->rconn;
+
+	return NULL;
+}
+
+static HTAB *
+createConnHash(void)
+{
+	HASHCTL		ctl;
+
+	ctl.keysize = NAMEDATALEN;
+	ctl.entrysize = sizeof(remoteConnHashEnt);
+
+	return hash_create("Remote Con hash", NUMCONN, &ctl,
+					   HASH_ELEM | HASH_STRINGS);
+}
+
+static void
+createNewConnection(const char *name, remoteConn *rconn)
+{
+	remoteConnHashEnt *hentry;
+	bool		found;
+	char	   *key;
+
+	if (!remoteConnHash)
+		remoteConnHash = createConnHash();
+
+	key = pstrdup(name);
+	truncate_identifier(key, strlen(key), true);
+	hentry = (remoteConnHashEnt *) hash_search(remoteConnHash, key,
+											   HASH_ENTER, &found);
+
+	if (found)
+	{
+		PQfinish(rconn->conn);
+		ReleaseExternalFD();
+		pfree(rconn);
+
+		ereport(ERROR,
+				(errcode(ERRCODE_DUPLICATE_OBJECT),
+				 errmsg("duplicate connection name")));
+	}
+
+	hentry->rconn = rconn;
+	strlcpy(hentry->name, name, sizeof(hentry->name));
+}
+
+static void
+deleteConnection(const char *name)
+{
+	remoteConnHashEnt *hentry;
+	bool		found;
+	char	   *key;
+
+	if (!remoteConnHash)
+		remoteConnHash = createConnHash();
+
+	key = pstrdup(name);
+	truncate_identifier(key, strlen(key), false);
+	hentry = (remoteConnHashEnt *) hash_search(remoteConnHash,
+											   key, HASH_REMOVE, &found);
+
+	if (!hentry)
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("undefined connection name")));
+}
+
+static void
+dblink_security_check(PGconn *conn, remoteConn *rconn)
+{
+	if (!superuser())
+	{
+		if (!PQconnectionUsedPassword(conn))
+		{
+			PQfinish(conn);
+			ReleaseExternalFD();
+			if (rconn)
+				pfree(rconn);
+
+			ereport(ERROR,
+					(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
+					 errmsg("password is required"),
+					 errdetail("Non-superuser cannot connect if the server does not request a password."),
+					 errhint("Target server's authentication method must be changed.")));
+		}
+	}
+}
+
+/*
+ * For non-superusers, insist that the connstr specify a password.  This
+ * prevents a password from being picked up from .pgpass, a service file,
+ * the environment, etc.  We don't want the postgres user's passwords
+ * to be accessible to non-superusers.
+ */
+static void
+dblink_connstr_check(const char *connstr)
+{
+	if (!superuser())
+	{
+		PQconninfoOption *options;
+		PQconninfoOption *option;
+		bool		connstr_gives_password = false;
+
+		options = PQconninfoParse(connstr, NULL);
+		if (options)
+		{
+			for (option = options; option->keyword != NULL; option++)
+			{
+				if (strcmp(option->keyword, "password") == 0)
+				{
+					if (option->val != NULL && option->val[0] != '\0')
+					{
+						connstr_gives_password = true;
+						break;
+					}
+				}
+			}
+			PQconninfoFree(options);
+		}
+
+		if (!connstr_gives_password)
+			ereport(ERROR,
+					(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
+					 errmsg("password is required"),
+					 errdetail("Non-superusers must provide a password in the connection string.")));
+	}
+}
+
+/*
+ * Report an error received from the remote server
+ *
+ * res: the received error result (will be freed)
+ * fail: true for ERROR ereport, false for NOTICE
+ * fmt and following args: sprintf-style format and values for errcontext;
+ * the resulting string should be worded like "while <some action>"
+ */
+static void
+dblink_res_error(PGconn *conn, const char *conname, PGresult *res,
+				 bool fail, const char *fmt,...)
+{
+	int			level;
+	char	   *pg_diag_sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);
+	char	   *pg_diag_message_primary = PQresultErrorField(res, PG_DIAG_MESSAGE_PRIMARY);
+	char	   *pg_diag_message_detail = PQresultErrorField(res, PG_DIAG_MESSAGE_DETAIL);
+	char	   *pg_diag_message_hint = PQresultErrorField(res, PG_DIAG_MESSAGE_HINT);
+	char	   *pg_diag_context = PQresultErrorField(res, PG_DIAG_CONTEXT);
+	int			sqlstate;
+	char	   *message_primary;
+	char	   *message_detail;
+	char	   *message_hint;
+	char	   *message_context;
+	va_list		ap;
+	char		dblink_context_msg[512];
+
+	if (fail)
+		level = ERROR;
+	else
+		level = NOTICE;
+
+	if (pg_diag_sqlstate)
+		sqlstate = MAKE_SQLSTATE(pg_diag_sqlstate[0],
+								 pg_diag_sqlstate[1],
+								 pg_diag_sqlstate[2],
+								 pg_diag_sqlstate[3],
+								 pg_diag_sqlstate[4]);
+	else
+		sqlstate = ERRCODE_CONNECTION_FAILURE;
+
+	message_primary = xpstrdup(pg_diag_message_primary);
+	message_detail = xpstrdup(pg_diag_message_detail);
+	message_hint = xpstrdup(pg_diag_message_hint);
+	message_context = xpstrdup(pg_diag_context);
+
+	/*
+	 * If we don't get a message from the PGresult, try the PGconn.  This is
+	 * needed because for connection-level failures, PQexec may just return
+	 * NULL, not a PGresult at all.
+	 */
+	if (message_primary == NULL)
+		message_primary = pchomp(PQerrorMessage(conn));
+
+	/*
+	 * Now that we've copied all the data we need out of the PGresult, it's
+	 * safe to free it.  We must do this to avoid PGresult leakage.  We're
+	 * leaking all the strings too, but those are in palloc'd memory that will
+	 * get cleaned up eventually.
+	 */
+	if (res)
+		PQclear(res);
+
+	/*
+	 * Format the basic errcontext string.  Below, we'll add on something
+	 * about the connection name.  That's a violation of the translatability
+	 * guidelines about constructing error messages out of parts, but since
+	 * there's no translation support for dblink, there's no need to worry
+	 * about that (yet).
+	 */
+	va_start(ap, fmt);
+	vsnprintf(dblink_context_msg, sizeof(dblink_context_msg), fmt, ap);
+	va_end(ap);
+
+	ereport(level,
+			(errcode(sqlstate),
+			 (message_primary != NULL && message_primary[0] != '\0') ?
+			 errmsg_internal("%s", message_primary) :
+			 errmsg("could not obtain message string for remote error"),
+			 message_detail ? errdetail_internal("%s", message_detail) : 0,
+			 message_hint ? errhint("%s", message_hint) : 0,
+			 message_context ? (errcontext("%s", message_context)) : 0,
+			 conname ?
+			 (errcontext("%s on dblink connection named \"%s\"",
+						 dblink_context_msg, conname)) :
+			 (errcontext("%s on unnamed dblink connection",
+						 dblink_context_msg))));
+}
+
+/*
+ * Obtain connection string for a foreign server
+ */
+static char *
+get_connect_string(const char *servername)
+{
+	ForeignServer *foreign_server = NULL;
+	UserMapping *user_mapping;
+	ListCell   *cell;
+	StringInfoData buf;
+	ForeignDataWrapper *fdw;
+	AclResult	aclresult;
+	char	   *srvname;
+
+	static const PQconninfoOption *options = NULL;
+
+	initStringInfo(&buf);
+
+	/*
+	 * Get list of valid libpq options.
+	 *
+	 * To avoid unnecessary work, we get the list once and use it throughout
+	 * the lifetime of this backend process.  We don't need to care about
+	 * memory context issues, because PQconndefaults allocates with malloc.
+	 */
+	if (!options)
+	{
+		options = PQconndefaults();
+		if (!options)			/* assume reason for failure is OOM */
+			ereport(ERROR,
+					(errcode(ERRCODE_FDW_OUT_OF_MEMORY),
+					 errmsg("out of memory"),
+					 errdetail("Could not get libpq's default connection options.")));
+	}
+
+	/* first gather the server connstr options */
+	srvname = pstrdup(servername);
+	truncate_identifier(srvname, strlen(srvname), false);
+	foreign_server = GetForeignServerByName(srvname, true);
+
+	if (foreign_server)
+	{
+		Oid			serverid = foreign_server->serverid;
+		Oid			fdwid = foreign_server->fdwid;
+		Oid			userid = GetUserId();
+
+		user_mapping = GetUserMapping(userid, serverid);
+		fdw = GetForeignDataWrapper(fdwid);
+
+		/* Check permissions, user must have usage on the server. */
+		aclresult = pg_foreign_server_aclcheck(serverid, userid, ACL_USAGE);
+		if (aclresult != ACLCHECK_OK)
+			aclcheck_error(aclresult, OBJECT_FOREIGN_SERVER, foreign_server->servername);
+
+		foreach(cell, fdw->options)
+		{
+			DefElem    *def = lfirst(cell);
+
+			if (is_valid_dblink_option(options, def->defname, ForeignDataWrapperRelationId))
+				appendStringInfo(&buf, "%s='%s' ", def->defname,
+								 escape_param_str(strVal(def->arg)));
+		}
+
+		foreach(cell, foreign_server->options)
+		{
+			DefElem    *def = lfirst(cell);
+
+			if (is_valid_dblink_option(options, def->defname, ForeignServerRelationId))
+				appendStringInfo(&buf, "%s='%s' ", def->defname,
+								 escape_param_str(strVal(def->arg)));
+		}
+
+		foreach(cell, user_mapping->options)
+		{
+
+			DefElem    *def = lfirst(cell);
+
+			if (is_valid_dblink_option(options, def->defname, UserMappingRelationId))
+				appendStringInfo(&buf, "%s='%s' ", def->defname,
+								 escape_param_str(strVal(def->arg)));
+		}
+
+		return buf.data;
+	}
+	else
+		return NULL;
+}
+
+/*
+ * Escaping libpq connect parameter strings.
+ *
+ * Replaces "'" with "\'" and "\" with "\\".
+ */
+static char *
+escape_param_str(const char *str)
+{
+	const char *cp;
+	StringInfoData buf;
+
+	initStringInfo(&buf);
+
+	for (cp = str; *cp; cp++)
+	{
+		if (*cp == '\\' || *cp == '\'')
+			appendStringInfoChar(&buf, '\\');
+		appendStringInfoChar(&buf, *cp);
+	}
+
+	return buf.data;
+}
+
+/*
+ * Validate the PK-attnums argument for dblink_build_sql_insert() and related
+ * functions, and translate to the internal representation.
+ *
+ * The user supplies an int2vector of 1-based logical attnums, plus a count
+ * argument (the need for the separate count argument is historical, but we
+ * still check it).  We check that each attnum corresponds to a valid,
+ * non-dropped attribute of the rel.  We do *not* prevent attnums from being
+ * listed twice, though the actual use-case for such things is dubious.
+ * Note that before Postgres 9.0, the user's attnums were interpreted as
+ * physical not logical column numbers; this was changed for future-proofing.
+ *
+ * The internal representation is a palloc'd int array of 0-based physical
+ * attnums.
+ */
+static void
+validate_pkattnums(Relation rel,
+				   int2vector *pkattnums_arg, int32 pknumatts_arg,
+				   int **pkattnums, int *pknumatts)
+{
+	TupleDesc	tupdesc = rel->rd_att;
+	int			natts = tupdesc->natts;
+	int			i;
+
+	/* Don't take more array elements than there are */
+	pknumatts_arg = Min(pknumatts_arg, pkattnums_arg->dim1);
+
+	/* Must have at least one pk attnum selected */
+	if (pknumatts_arg <= 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("number of key attributes must be > 0")));
+
+	/* Allocate output array */
+	*pkattnums = (int *) palloc(pknumatts_arg * sizeof(int));
+	*pknumatts = pknumatts_arg;
+
+	/* Validate attnums and convert to internal form */
+	for (i = 0; i < pknumatts_arg; i++)
+	{
+		int			pkattnum = pkattnums_arg->values[i];
+		int			lnum;
+		int			j;
+
+		/* Can throw error immediately if out of range */
+		if (pkattnum <= 0 || pkattnum > natts)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("invalid attribute number %d", pkattnum)));
+
+		/* Identify which physical column has this logical number */
+		lnum = 0;
+		for (j = 0; j < natts; j++)
+		{
+			/* dropped columns don't count */
+			if (TupleDescAttr(tupdesc, j)->attisdropped)
+				continue;
+
+			if (++lnum == pkattnum)
+				break;
+		}
+
+		if (j < natts)
+			(*pkattnums)[i] = j;
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("invalid attribute number %d", pkattnum)));
+	}
+}
+
+/*
+ * Check if the specified connection option is valid.
+ *
+ * We basically allow whatever libpq thinks is an option, with these
+ * restrictions:
+ *		debug options: disallowed
+ *		"client_encoding": disallowed
+ *		"user": valid only in USER MAPPING options
+ *		secure options (eg password): valid only in USER MAPPING options
+ *		others: valid only in FOREIGN SERVER options
+ *
+ * We disallow client_encoding because it would be overridden anyway via
+ * PQclientEncoding; allowing it to be specified would merely promote
+ * confusion.
+ */
+static bool
+is_valid_dblink_option(const PQconninfoOption *options, const char *option,
+					   Oid context)
+{
+	const PQconninfoOption *opt;
+
+	/* Look up the option in libpq result */
+	for (opt = options; opt->keyword; opt++)
+	{
+		if (strcmp(opt->keyword, option) == 0)
+			break;
+	}
+	if (opt->keyword == NULL)
+		return false;
+
+	/* Disallow debug options (particularly "replication") */
+	if (strchr(opt->dispchar, 'D'))
+		return false;
+
+	/* Disallow "client_encoding" */
+	if (strcmp(opt->keyword, "client_encoding") == 0)
+		return false;
+
+	/*
+	 * If the option is "user" or marked secure, it should be specified only
+	 * in USER MAPPING.  Others should be specified only in SERVER.
+	 */
+	if (strcmp(opt->keyword, "user") == 0 || strchr(opt->dispchar, '*'))
+	{
+		if (context != UserMappingRelationId)
+			return false;
+	}
+	else
+	{
+		if (context != ForeignServerRelationId)
+			return false;
+	}
+
+	return true;
+}
+
+/*
+ * Copy the remote session's values of GUCs that affect datatype I/O
+ * and apply them locally in a new GUC nesting level.  Returns the new
+ * nestlevel (which is needed by restoreLocalGucs to undo the settings),
+ * or -1 if no new nestlevel was needed.
+ *
+ * We use the equivalent of a function SET option to allow the settings to
+ * persist only until the caller calls restoreLocalGucs.  If an error is
+ * thrown in between, guc.c will take care of undoing the settings.
+ */
+static int
+applyRemoteGucs(PGconn *conn)
+{
+	static const char *const GUCsAffectingIO[] = {
+		"DateStyle",
+		"IntervalStyle"
+	};
+
+	int			nestlevel = -1;
+	int			i;
+
+	for (i = 0; i < lengthof(GUCsAffectingIO); i++)
+	{
+		const char *gucName = GUCsAffectingIO[i];
+		const char *remoteVal = PQparameterStatus(conn, gucName);
+		const char *localVal;
+
+		/*
+		 * If the remote server is pre-8.4, it won't have IntervalStyle, but
+		 * that's okay because its output format won't be ambiguous.  So just
+		 * skip the GUC if we don't get a value for it.  (We might eventually
+		 * need more complicated logic with remote-version checks here.)
+		 */
+		if (remoteVal == NULL)
+			continue;
+
+		/*
+		 * Avoid GUC-setting overhead if the remote and local GUCs already
+		 * have the same value.
+		 */
+		localVal = GetConfigOption(gucName, false, false);
+		Assert(localVal != NULL);
+
+		if (strcmp(remoteVal, localVal) == 0)
+			continue;
+
+		/* Create new GUC nest level if we didn't already */
+		if (nestlevel < 0)
+			nestlevel = NewGUCNestLevel();
+
+		/* Apply the option (this will throw error on failure) */
+		(void) set_config_option(gucName, remoteVal,
+								 PGC_USERSET, PGC_S_SESSION,
+								 GUC_ACTION_SAVE, true, 0, false);
+	}
+
+	return nestlevel;
+}
+
+/*
+ * Restore local GUCs after they have been overlaid with remote settings.
+ */
+static void
+restoreLocalGucs(int nestlevel)
+{
+	/* Do nothing if no new nestlevel was created */
+	if (nestlevel > 0)
+		AtEOXact_GUC(true, nestlevel);
+}