postgres/contrib/dblink/dblink.c

/*
 * 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>
 *
 * Copyright (c) 2001, 2002, 2003 by 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 "libpq-fe.h"
#include "fmgr.h"
#include "funcapi.h"
#include "access/tupdesc.h"
#include "access/heapam.h"
#include "catalog/catname.h"
#include "catalog/namespace.h"
#include "catalog/pg_index.h"
#include "catalog/pg_type.h"
#include "executor/executor.h"
#include "executor/spi.h"
#include "lib/stringinfo.h"
#include "nodes/nodes.h"
#include "nodes/execnodes.h"
#include "nodes/pg_list.h"
#include "parser/parse_type.h"
#include "tcop/tcopprot.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/array.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"
#include "utils/dynahash.h"
#include "utils/hsearch.h"
#include "utils/memutils.h"

#include "dblink.h"

typedef struct remoteConn
{
	PGconn *con;			/* Hold the remote connection */
	bool remoteTrFlag;		/* Indicates whether or not a transaction
							 * on remote database is in progress*/
} remoteConn;

/*
 * Internal declarations
 */
static remoteConn *getConnectionByName(const char *name);
static HTAB *createConnHash(void);
static void createNewConnection(const char *name,remoteConn *con);
static void deleteConnection(const char *name);
static char **get_pkey_attnames(Oid relid, int16 *numatts);
static char *get_sql_insert(Oid relid, int16 *pkattnums, int16 pknumatts, char **src_pkattvals, char **tgt_pkattvals);
static char *get_sql_delete(Oid relid, int16 *pkattnums, int16 pknumatts, char **tgt_pkattvals);
static char *get_sql_update(Oid relid, int16 *pkattnums, int16 pknumatts, char **src_pkattvals, char **tgt_pkattvals);
static char *quote_literal_cstr(char *rawstr);
static char *quote_ident_cstr(char *rawstr);
static int16 get_attnum_pk_pos(int16 *pkattnums, int16 pknumatts, int16 key);
static HeapTuple get_tuple_of_interest(Oid relid, int16 *pkattnums, int16 pknumatts, char **src_pkattvals);
static Oid	get_relid_from_relname(text *relname_text);
static TupleDesc pgresultGetTupleDesc(PGresult *res);
static char *generate_relation_name(Oid relid);

/* Global */
List   *res_id = NIL;
int		res_id_index = 0;
PGconn *persistent_conn = 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 *rcon;
} remoteConnHashEnt;

/* initial number of connection hashes */
#define NUMCONN 16

/* general utility */
#define GET_TEXT(cstrp) DatumGetTextP(DirectFunctionCall1(textin, CStringGetDatum(cstrp)))
#define GET_STR(textp) DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(textp)))
#define xpfree(var_) \
	do { \
		if (var_ != NULL) \
		{ \
			pfree(var_); \
			var_ = NULL; \
		} \
	} while (0)
#define DBLINK_RES_INTERNALERROR(p2) \
	do { \
			msg = pstrdup(PQerrorMessage(conn)); \
			if (res) \
				PQclear(res); \
			elog(ERROR, "%s: %s", p2, msg); \
	} while (0)
#define DBLINK_RES_ERROR(p2) \
	do { \
			msg = pstrdup(PQerrorMessage(conn)); \
			if (res) \
				PQclear(res); \
			ereport(ERROR, \
					(errcode(ERRCODE_SYNTAX_ERROR), \
					 errmsg("%s", p2), \
					 errdetail("%s", msg))); \
	} while (0)
#define DBLINK_CONN_NOT_AVAIL \
	do { \
		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"))); \
	} while (0)
#define DBLINK_GET_CONN \
	do { \
			char *conname_or_str = GET_STR(PG_GETARG_TEXT_P(0)); \
			rcon = getConnectionByName(conname_or_str); \
			if(rcon) \
			{ \
				conn = rcon->con; \
				freeconn = false; \
			} \
			else \
			{ \
				connstr = conname_or_str; \
				conn = PQconnectdb(connstr); \
				if (PQstatus(conn) == CONNECTION_BAD) \
				{ \
					msg = pstrdup(PQerrorMessage(conn)); \
					PQfinish(conn); \
					ereport(ERROR, \
							(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION), \
							 errmsg("could not establish connection"), \
							 errdetail("%s", msg))); \
				} \
			} \
	} while (0)


/*
 * Create a persistent connection to another database
 */
PG_FUNCTION_INFO_V1(dblink_connect);
Datum
dblink_connect(PG_FUNCTION_ARGS)
{
	char	   *connstr = NULL;
	char	   *connname = NULL;
	char	   *msg;
	MemoryContext oldcontext;
	PGconn	   *conn = NULL;
	remoteConn *rcon = NULL;

	if(PG_NARGS()==2)
	{
		connstr = GET_STR(PG_GETARG_TEXT_P(1));
		connname = GET_STR(PG_GETARG_TEXT_P(0));
	}
	else if(PG_NARGS()==1)
		connstr = GET_STR(PG_GETARG_TEXT_P(0));

	oldcontext = MemoryContextSwitchTo(TopMemoryContext);

	if(connname)
		rcon=(remoteConn *) palloc(sizeof(remoteConn));
	conn = PQconnectdb(connstr);

	MemoryContextSwitchTo(oldcontext);

	if (PQstatus(conn) == CONNECTION_BAD)
	{
		msg = pstrdup(PQerrorMessage(conn));
		PQfinish(conn);
		if(rcon)
			pfree(rcon);

		ereport(ERROR,
				(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
				 errmsg("could not establish connection"),
				 errdetail("%s", msg)));
	}

	if(connname)
	{
		rcon->con = conn;
		createNewConnection(connname, rcon);
	}
	else
		persistent_conn = conn;

	PG_RETURN_TEXT_P(GET_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 *rcon = NULL;
	PGconn	   *conn = NULL;

	if (PG_NARGS() ==1 )
	{
		conname = GET_STR(PG_GETARG_TEXT_P(0));
		rcon = getConnectionByName(conname);
		if (rcon)
			conn = rcon->con;
	}
	else
		conn = persistent_conn;

	if (!conn)
		DBLINK_CONN_NOT_AVAIL;

	PQfinish(conn);
	if (rcon)
	{
		deleteConnection(conname);
		pfree(rcon);
	}

	PG_RETURN_TEXT_P(GET_TEXT("OK"));
}

/*
 * opens a cursor using a persistent connection
 */
PG_FUNCTION_INFO_V1(dblink_open);
Datum
dblink_open(PG_FUNCTION_ARGS)
{
	char	   *msg;
	PGresult   *res = NULL;
	PGconn	   *conn = NULL;
	char	   *curname = NULL;
	char	   *sql = NULL;
	char	   *conname = NULL;
	StringInfo	str = makeStringInfo();
	remoteConn *rcon = NULL;

	if(PG_NARGS() == 2)
	{
		curname = GET_STR(PG_GETARG_TEXT_P(0));
		sql = GET_STR(PG_GETARG_TEXT_P(1));
		conn = persistent_conn;
	}
	else if(PG_NARGS() == 3)
	{
		conname = GET_STR(PG_GETARG_TEXT_P(0));
		curname = GET_STR(PG_GETARG_TEXT_P(1));
		sql = GET_STR(PG_GETARG_TEXT_P(2));
		rcon = getConnectionByName(conname);
		if (rcon)
			conn = rcon->con;
	}

	if (!conn)
		DBLINK_CONN_NOT_AVAIL;

	res = PQexec(conn, "BEGIN");
	if (PQresultStatus(res) != PGRES_COMMAND_OK)
		DBLINK_RES_INTERNALERROR("begin error");

	PQclear(res);

	appendStringInfo(str, "DECLARE %s CURSOR FOR %s", curname, sql);
	res = PQexec(conn, str->data);
	if (!res ||
		(PQresultStatus(res) != PGRES_COMMAND_OK &&
		 PQresultStatus(res) != PGRES_TUPLES_OK))
		DBLINK_RES_ERROR("sql error");

	PQclear(res);

	PG_RETURN_TEXT_P(GET_TEXT("OK"));
}

/*
 * closes a cursor
 */
PG_FUNCTION_INFO_V1(dblink_close);
Datum
dblink_close(PG_FUNCTION_ARGS)
{
	PGconn	   *conn = NULL;
	PGresult   *res = NULL;
	char	   *curname = NULL;
	char	   *conname = NULL;
	StringInfo	str = makeStringInfo();
	char	   *msg;
	remoteConn *rcon = NULL;

	if (PG_NARGS() == 1)
	{
		curname = GET_STR(PG_GETARG_TEXT_P(0));
		conn = persistent_conn;
	}
	else if (PG_NARGS()==2)
	{
		conname = GET_STR(PG_GETARG_TEXT_P(0));
		curname = GET_STR(PG_GETARG_TEXT_P(1));
		rcon = getConnectionByName(conname);
		if(rcon)
			conn = rcon->con;
	}

	if (!conn)
		DBLINK_CONN_NOT_AVAIL;

	appendStringInfo(str, "CLOSE %s", curname);

	/* close the cursor */
	res = PQexec(conn, str->data);
	if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
		DBLINK_RES_ERROR("sql error");

	PQclear(res);

	/* commit the transaction */
	res = PQexec(conn, "COMMIT");
	if (PQresultStatus(res) != PGRES_COMMAND_OK)
		DBLINK_RES_INTERNALERROR("commit error");

	PQclear(res);

	PG_RETURN_TEXT_P(GET_TEXT("OK"));
}

/*
 * Fetch results from an open cursor
 */
PG_FUNCTION_INFO_V1(dblink_fetch);
Datum
dblink_fetch(PG_FUNCTION_ARGS)
{
	FuncCallContext *funcctx;
	TupleDesc	tupdesc = NULL;
	int			call_cntr;
	int			max_calls;
	TupleTableSlot *slot;
	AttInMetadata *attinmeta;
	char	   *msg;
	PGresult   *res = NULL;
	MemoryContext oldcontext;
	char	   *conname = NULL;
	remoteConn *rcon=NULL;

	/* stuff done only on the first call of the function */
	if (SRF_IS_FIRSTCALL())
	{
		Oid			functypeid;
		char		functyptype;
		Oid			funcid = fcinfo->flinfo->fn_oid;
		PGconn	   *conn = NULL;
		StringInfo	str = makeStringInfo();
		char	   *curname = NULL;
		int			howmany = 0;

		if (PG_NARGS() == 3)
		{
			conname = GET_STR(PG_GETARG_TEXT_P(0));
			curname = GET_STR(PG_GETARG_TEXT_P(1));
			howmany = PG_GETARG_INT32(2);

			rcon = getConnectionByName(conname);
			if(rcon)
				conn = rcon->con;
		}
		else if (PG_NARGS() == 2)
		{
			curname = GET_STR(PG_GETARG_TEXT_P(0));
			howmany = PG_GETARG_INT32(1);
			conn = persistent_conn;
		}

		if(!conn)
			DBLINK_CONN_NOT_AVAIL;

		/* 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);

		appendStringInfo(str, "FETCH %d FROM %s", howmany, curname);

		res = PQexec(conn, str->data);
		if (!res ||
			(PQresultStatus(res) != PGRES_COMMAND_OK &&
			 PQresultStatus(res) != PGRES_TUPLES_OK))
		{
			DBLINK_RES_ERROR("sql error");
		}
		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)));
		}

		funcctx->max_calls = PQntuples(res);

		/* got results, keep track of them */
		funcctx->user_fctx = res;

		/* fast track when no results */
		if (funcctx->max_calls < 1)
			SRF_RETURN_DONE(funcctx);

		/* check typtype to see if we have a predetermined return type */
		functypeid = get_func_rettype(funcid);
		functyptype = get_typtype(functypeid);

		if (functyptype == 'c')
			tupdesc = TypeGetTupleDesc(functypeid, NIL);
		else if (functyptype == 'p' && functypeid == RECORDOID)
			tupdesc = pgresultGetTupleDesc(res);
		else
			/* shouldn't happen */
			elog(ERROR, "return type must be a row type");

		/* store needed metadata for subsequent calls */
		slot = TupleDescGetSlot(tupdesc);
		funcctx->slot = slot;
		attinmeta = TupleDescGetAttInMetadata(tupdesc);
		funcctx->attinmeta = attinmeta;

		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;

	slot = funcctx->slot;

	res = (PGresult *) funcctx->user_fctx;
	attinmeta = funcctx->attinmeta;
	tupdesc = attinmeta->tupdesc;

	if (call_cntr < max_calls)	/* do when there is more left to send */
	{
		char	  **values;
		HeapTuple	tuple;
		Datum		result;
		int			i;
		int			nfields = PQnfields(res);

		values = (char **) palloc(nfields * sizeof(char *));
		for (i = 0; i < nfields; i++)
		{
			if (PQgetisnull(res, call_cntr, i) == 0)
				values[i] = PQgetvalue(res, call_cntr, i);
			else
				values[i] = NULL;
		}

		/* build the tuple */
		tuple = BuildTupleFromCStrings(attinmeta, values);

		/* make the tuple into a datum */
		result = TupleGetDatum(slot, tuple);

		SRF_RETURN_NEXT(funcctx, result);
	}
	else
	{
		/* do when there is no more left */
		PQclear(res);
		SRF_RETURN_DONE(funcctx);
	}
}

/*
 * Note: this is the new preferred version of dblink
 */
PG_FUNCTION_INFO_V1(dblink_record);
Datum
dblink_record(PG_FUNCTION_ARGS)
{
	FuncCallContext *funcctx;
	TupleDesc	tupdesc = NULL;
	int			call_cntr;
	int			max_calls;
	TupleTableSlot *slot;
	AttInMetadata *attinmeta;
	char	   *msg;
	PGresult   *res = NULL;
	bool		is_sql_cmd = false;
	char	   *sql_cmd_status = NULL;
	MemoryContext oldcontext;
	bool		freeconn = true;

	/* stuff done only on the first call of the function */
	if (SRF_IS_FIRSTCALL())
	{
		Oid			functypeid;
		char		functyptype;
		Oid			funcid = fcinfo->flinfo->fn_oid;
		PGconn	   *conn = NULL;
		char	   *connstr = NULL;
		char	   *sql = NULL;
		char	   *conname = NULL;
		remoteConn *rcon=NULL;

		/* 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);

		if (PG_NARGS() == 2)
		{
			DBLINK_GET_CONN;
			sql = GET_STR(PG_GETARG_TEXT_P(1));
		}
		else if (PG_NARGS() == 1)
		{
			conn = persistent_conn;
			sql = GET_STR(PG_GETARG_TEXT_P(0));
		}
		else
			/* shouldn't happen */
			elog(ERROR, "wrong number of arguments");

		if(!conn)
			DBLINK_CONN_NOT_AVAIL;

		res = PQexec(conn, sql);
		if (!res || (PQresultStatus(res) != PGRES_COMMAND_OK && PQresultStatus(res) != PGRES_TUPLES_OK))
			DBLINK_RES_ERROR("sql error");

		if (PQresultStatus(res) == PGRES_COMMAND_OK)
		{
			is_sql_cmd = true;

			/* need a tuple descriptor representing one TEXT column */
			tupdesc = CreateTemplateTupleDesc(1, false);
			TupleDescInitEntry(tupdesc, (AttrNumber) 1, "status",
							   TEXTOID, -1, 0, false);

			/*
			 * and save a copy of the command status string to return
			 * as our result tuple
			 */
			sql_cmd_status = PQcmdStatus(res);
			funcctx->max_calls = 1;
		}
		else
			funcctx->max_calls = PQntuples(res);

		/* got results, keep track of them */
		funcctx->user_fctx = res;

		/* if needed, close the connection to the database and cleanup */
		if (freeconn && PG_NARGS() == 2)
			PQfinish(conn);

		/* fast track when no results */
		if (funcctx->max_calls < 1)
			SRF_RETURN_DONE(funcctx);

		/* check typtype to see if we have a predetermined return type */
		functypeid = get_func_rettype(funcid);
		functyptype = get_typtype(functypeid);

		if (!is_sql_cmd)
		{
			if (functyptype == 'c')
				tupdesc = TypeGetTupleDesc(functypeid, NIL);
			else if (functyptype == 'p' && functypeid == RECORDOID)
				tupdesc = pgresultGetTupleDesc(res);
			else
				/* shouldn't happen */
				elog(ERROR, "return type must be a row type");
		}

		/* store needed metadata for subsequent calls */
		slot = TupleDescGetSlot(tupdesc);
		funcctx->slot = slot;
		attinmeta = TupleDescGetAttInMetadata(tupdesc);
		funcctx->attinmeta = attinmeta;

		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;

	slot = funcctx->slot;

	res = (PGresult *) funcctx->user_fctx;
	attinmeta = funcctx->attinmeta;
	tupdesc = attinmeta->tupdesc;

	if (call_cntr < max_calls)	/* do when there is more left to send */
	{
		char	  **values;
		HeapTuple	tuple;
		Datum		result;

		if (!is_sql_cmd)
		{
			int			i;
			int			nfields = PQnfields(res);

			values = (char **) palloc(nfields * sizeof(char *));
			for (i = 0; i < nfields; i++)
			{
				if (PQgetisnull(res, call_cntr, i) == 0)
					values[i] = PQgetvalue(res, call_cntr, i);
				else
					values[i] = NULL;
			}
		}
		else
		{
			values = (char **) palloc(1 * sizeof(char *));
			values[0] = sql_cmd_status;
		}

		/* build the tuple */
		tuple = BuildTupleFromCStrings(attinmeta, values);

		/* make the tuple into a datum */
		result = TupleGetDatum(slot, tuple);

		SRF_RETURN_NEXT(funcctx, result);
	}
	else
	{
		/* do when there is no more left */
		PQclear(res);
		SRF_RETURN_DONE(funcctx);
	}
}

/*
 * Execute an SQL non-SELECT command
 */
PG_FUNCTION_INFO_V1(dblink_exec);
Datum
dblink_exec(PG_FUNCTION_ARGS)
{
	char	   *msg;
	PGresult   *res = NULL;
	text	   *sql_cmd_status = NULL;
	TupleDesc	tupdesc = NULL;
	PGconn	   *conn = NULL;
	char	   *connstr = NULL;
	char	   *sql = NULL;
	char	   *conname = NULL;
	remoteConn *rcon=NULL;
	bool		freeconn = true;

	if (PG_NARGS() == 2)
	{
		DBLINK_GET_CONN;
		sql = GET_STR(PG_GETARG_TEXT_P(1));
	}
	else if (PG_NARGS() == 1)
	{
		conn = persistent_conn;
		sql = GET_STR(PG_GETARG_TEXT_P(0));
	}
	else
		/* shouldn't happen */
		elog(ERROR, "wrong number of arguments");

	if(!conn)
		DBLINK_CONN_NOT_AVAIL;

	res = PQexec(conn, sql);
	if (!res ||
		(PQresultStatus(res) != PGRES_COMMAND_OK &&
		 PQresultStatus(res) != PGRES_TUPLES_OK))
		DBLINK_RES_ERROR("sql error");

	if (PQresultStatus(res) == PGRES_COMMAND_OK)
	{
		/* need a tuple descriptor representing one TEXT column */
		tupdesc = CreateTemplateTupleDesc(1, false);
		TupleDescInitEntry(tupdesc, (AttrNumber) 1, "status",
						   TEXTOID, -1, 0, false);

		/*
		 * and save a copy of the command status string to return as
		 * our result tuple
		 */
		sql_cmd_status = GET_TEXT(PQcmdStatus(res));
	}
	else
		ereport(ERROR,
				(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
				 errmsg("statement returning results not allowed")));

	PQclear(res);

	/* if needed, close the connection to the database and cleanup */
	if (freeconn && fcinfo->nargs == 2)
		PQfinish(conn);

	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		numatts;
	Oid			relid;
	char	  **results;
	FuncCallContext *funcctx;
	int32		call_cntr;
	int32		max_calls;
	TupleTableSlot *slot;
	AttInMetadata *attinmeta;
	MemoryContext oldcontext;

	/* stuff done only on the first call of the function */
	if (SRF_IS_FIRSTCALL())
	{
		TupleDesc	tupdesc = NULL;

		/* 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);

		/* convert relname to rel Oid */
		relid = get_relid_from_relname(PG_GETARG_TEXT_P(0));
		if (!OidIsValid(relid))
			ereport(ERROR,
					(errcode(ERRCODE_UNDEFINED_TABLE),
					 errmsg("relation \"%s\" does not exist",
							GET_STR(PG_GETARG_TEXT_P(0)))));
		/*
		 * need a tuple descriptor representing one INT and one TEXT
		 * column
		 */
		tupdesc = CreateTemplateTupleDesc(2, false);
		TupleDescInitEntry(tupdesc, (AttrNumber) 1, "position",
						   INT4OID, -1, 0, false);
		TupleDescInitEntry(tupdesc, (AttrNumber) 2, "colname",
						   TEXTOID, -1, 0, false);

		/* allocate a slot for a tuple with this tupdesc */
		slot = TupleDescGetSlot(tupdesc);

		/* assign slot to function context */
		funcctx->slot = slot;

		/*
		 * Generate attribute metadata needed later to produce tuples from
		 * raw C strings
		 */
		attinmeta = TupleDescGetAttInMetadata(tupdesc);
		funcctx->attinmeta = attinmeta;

		/* get an array of attnums */
		results = get_pkey_attnames(relid, &numatts);

		if ((results != NULL) && (numatts > 0))
		{
			funcctx->max_calls = numatts;

			/* got results, keep track of them */
			funcctx->user_fctx = results;
		}
		else
			/* fast track when no results */
			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;

	slot = funcctx->slot;

	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] = (char *) palloc(12);		/* sign, 10 digits, '\0' */

		sprintf(values[0], "%d", call_cntr + 1);

		values[1] = results[call_cntr];

		/* build the tuple */
		tuple = BuildTupleFromCStrings(attinmeta, values);

		/* make the tuple into a datum */
		result = TupleGetDatum(slot, tuple);

		SRF_RETURN_NEXT(funcctx, result);
	}
	else
	{
		/* do when there is no more left */
		SRF_RETURN_DONE(funcctx);
	}
}


#ifndef SHRT_MAX
#define SHRT_MAX (0x7FFF)
#endif
/*
 * 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)
{
	Oid			relid;
	text	   *relname_text;
	int16	   *pkattnums;
	int			pknumatts_tmp;
	int16		pknumatts = 0;
	char	  **src_pkattvals;
	char	  **tgt_pkattvals;
	ArrayType  *src_pkattvals_arry;
	ArrayType  *tgt_pkattvals_arry;
	int			src_ndim;
	int		   *src_dim;
	int			src_nitems;
	int			tgt_ndim;
	int		   *tgt_dim;
	int			tgt_nitems;
	int			i;
	char	   *ptr;
	char	   *sql;
	int16		typlen;
	bool		typbyval;
	char		typalign;

	relname_text = PG_GETARG_TEXT_P(0);

	/*
	 * Convert relname to rel OID.
	 */
	relid = get_relid_from_relname(relname_text);
	if (!OidIsValid(relid))
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_TABLE),
				 errmsg("relation \"%s\" does not exist",
						GET_STR(relname_text))));

	pkattnums = (int16 *) PG_GETARG_POINTER(1);
	pknumatts_tmp = PG_GETARG_INT32(2);
	if (pknumatts_tmp <= SHRT_MAX)
		pknumatts = pknumatts_tmp;
	else
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("input for number of primary key " \
						"attributes too large")));

	/*
	 * There should be at least one key attribute
	 */
	if (pknumatts == 0)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("number of key attributes must be > 0")));

	src_pkattvals_arry = PG_GETARG_ARRAYTYPE_P(3);
	tgt_pkattvals_arry = PG_GETARG_ARRAYTYPE_P(4);

	/*
	 * Source array is made up of key values that will be used to locate
	 * the tuple of interest from the local system.
	 */
	src_ndim = ARR_NDIM(src_pkattvals_arry);
	src_dim = ARR_DIMS(src_pkattvals_arry);
	src_nitems = ArrayGetNItems(src_ndim, src_dim);

	/*
	 * 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")));

	/*
	 * get array of pointers to c-strings from the input source array
	 */
	Assert(ARR_ELEMTYPE(src_pkattvals_arry) == TEXTOID);
	get_typlenbyvalalign(ARR_ELEMTYPE(src_pkattvals_arry),
						 &typlen, &typbyval, &typalign);

	src_pkattvals = (char **) palloc(src_nitems * sizeof(char *));
	ptr = ARR_DATA_PTR(src_pkattvals_arry);
	for (i = 0; i < src_nitems; i++)
	{
		src_pkattvals[i] = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(ptr)));
		ptr = att_addlength(ptr, typlen, PointerGetDatum(ptr));
		ptr = (char *) att_align(ptr, typalign);
	}

	/*
	 * Target array is made up of key values that will be used to build
	 * the SQL string for use on the remote system.
	 */
	tgt_ndim = ARR_NDIM(tgt_pkattvals_arry);
	tgt_dim = ARR_DIMS(tgt_pkattvals_arry);
	tgt_nitems = ArrayGetNItems(tgt_ndim, tgt_dim);

	/*
	 * 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")));

	/*
	 * get array of pointers to c-strings from the input target array
	 */
	Assert(ARR_ELEMTYPE(tgt_pkattvals_arry) == TEXTOID);
	get_typlenbyvalalign(ARR_ELEMTYPE(tgt_pkattvals_arry),
						 &typlen, &typbyval, &typalign);

	tgt_pkattvals = (char **) palloc(tgt_nitems * sizeof(char *));
	ptr = ARR_DATA_PTR(tgt_pkattvals_arry);
	for (i = 0; i < tgt_nitems; i++)
	{
		tgt_pkattvals[i] = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(ptr)));
		ptr = att_addlength(ptr, typlen, PointerGetDatum(ptr));
		ptr = (char *) att_align(ptr, typalign);
	}

	/*
	 * Prep work is finally done. Go get the SQL string.
	 */
	sql = get_sql_insert(relid, pkattnums, pknumatts, src_pkattvals, tgt_pkattvals);

	/*
	 * And send it
	 */
	PG_RETURN_TEXT_P(GET_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)
{
	Oid			relid;
	text	   *relname_text;
	int16	   *pkattnums;
	int			pknumatts_tmp;
	int16		pknumatts = 0;
	char	  **tgt_pkattvals;
	ArrayType  *tgt_pkattvals_arry;
	int			tgt_ndim;
	int		   *tgt_dim;
	int			tgt_nitems;
	int			i;
	char	   *ptr;
	char	   *sql;
	int16		typlen;
	bool		typbyval;
	char		typalign;

	relname_text = PG_GETARG_TEXT_P(0);

	/*
	 * Convert relname to rel OID.
	 */
	relid = get_relid_from_relname(relname_text);
	if (!OidIsValid(relid))
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_TABLE),
				 errmsg("relation \"%s\" does not exist",
						GET_STR(relname_text))));

	pkattnums = (int16 *) PG_GETARG_POINTER(1);
	pknumatts_tmp = PG_GETARG_INT32(2);
	if (pknumatts_tmp <= SHRT_MAX)
		pknumatts = pknumatts_tmp;
	else
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("input for number of primary key " \
						"attributes too large")));

	/*
	 * There should be at least one key attribute
	 */
	if (pknumatts == 0)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("number of key attributes must be > 0")));

	tgt_pkattvals_arry = PG_GETARG_ARRAYTYPE_P(3);

	/*
	 * Target array is made up of key values that will be used to build
	 * the SQL string for use on the remote system.
	 */
	tgt_ndim = ARR_NDIM(tgt_pkattvals_arry);
	tgt_dim = ARR_DIMS(tgt_pkattvals_arry);
	tgt_nitems = ArrayGetNItems(tgt_ndim, tgt_dim);

	/*
	 * 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")));

	/*
	 * get array of pointers to c-strings from the input target array
	 */
	Assert(ARR_ELEMTYPE(tgt_pkattvals_arry) == TEXTOID);
	get_typlenbyvalalign(ARR_ELEMTYPE(tgt_pkattvals_arry),
						 &typlen, &typbyval, &typalign);

	tgt_pkattvals = (char **) palloc(tgt_nitems * sizeof(char *));
	ptr = ARR_DATA_PTR(tgt_pkattvals_arry);
	for (i = 0; i < tgt_nitems; i++)
	{
		tgt_pkattvals[i] = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(ptr)));
		ptr = att_addlength(ptr, typlen, PointerGetDatum(ptr));
		ptr = (char *) att_align(ptr, typalign);
	}

	/*
	 * Prep work is finally done. Go get the SQL string.
	 */
	sql = get_sql_delete(relid, pkattnums, pknumatts, tgt_pkattvals);

	/*
	 * And send it
	 */
	PG_RETURN_TEXT_P(GET_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)
{
	Oid			relid;
	text	   *relname_text;
	int16	   *pkattnums;
	int			pknumatts_tmp;
	int16		pknumatts = 0;
	char	  **src_pkattvals;
	char	  **tgt_pkattvals;
	ArrayType  *src_pkattvals_arry;
	ArrayType  *tgt_pkattvals_arry;
	int			src_ndim;
	int		   *src_dim;
	int			src_nitems;
	int			tgt_ndim;
	int		   *tgt_dim;
	int			tgt_nitems;
	int			i;
	char	   *ptr;
	char	   *sql;
	int16		typlen;
	bool		typbyval;
	char		typalign;

	relname_text = PG_GETARG_TEXT_P(0);

	/*
	 * Convert relname to rel OID.
	 */
	relid = get_relid_from_relname(relname_text);
	if (!OidIsValid(relid))
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_TABLE),
				 errmsg("relation \"%s\" does not exist",
						GET_STR(relname_text))));

	pkattnums = (int16 *) PG_GETARG_POINTER(1);
	pknumatts_tmp = PG_GETARG_INT32(2);
	if (pknumatts_tmp <= SHRT_MAX)
		pknumatts = pknumatts_tmp;
	else
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("input for number of primary key " \
						"attributes too large")));

	/*
	 * There should be one source array key values for each key attnum
	 */
	if (pknumatts == 0)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("number of key attributes must be > 0")));

	src_pkattvals_arry = PG_GETARG_ARRAYTYPE_P(3);
	tgt_pkattvals_arry = PG_GETARG_ARRAYTYPE_P(4);

	/*
	 * Source array is made up of key values that will be used to locate
	 * the tuple of interest from the local system.
	 */
	src_ndim = ARR_NDIM(src_pkattvals_arry);
	src_dim = ARR_DIMS(src_pkattvals_arry);
	src_nitems = ArrayGetNItems(src_ndim, src_dim);

	/*
	 * 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")));

	/*
	 * get array of pointers to c-strings from the input source array
	 */
	Assert(ARR_ELEMTYPE(src_pkattvals_arry) == TEXTOID);
	get_typlenbyvalalign(ARR_ELEMTYPE(src_pkattvals_arry),
						 &typlen, &typbyval, &typalign);

	src_pkattvals = (char **) palloc(src_nitems * sizeof(char *));
	ptr = ARR_DATA_PTR(src_pkattvals_arry);
	for (i = 0; i < src_nitems; i++)
	{
		src_pkattvals[i] = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(ptr)));
		ptr = att_addlength(ptr, typlen, PointerGetDatum(ptr));
		ptr = (char *) att_align(ptr, typalign);
	}

	/*
	 * Target array is made up of key values that will be used to build
	 * the SQL string for use on the remote system.
	 */
	tgt_ndim = ARR_NDIM(tgt_pkattvals_arry);
	tgt_dim = ARR_DIMS(tgt_pkattvals_arry);
	tgt_nitems = ArrayGetNItems(tgt_ndim, tgt_dim);

	/*
	 * 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")));

	/*
	 * get array of pointers to c-strings from the input target array
	 */
	Assert(ARR_ELEMTYPE(tgt_pkattvals_arry) == TEXTOID);
	get_typlenbyvalalign(ARR_ELEMTYPE(tgt_pkattvals_arry),
						 &typlen, &typbyval, &typalign);

	tgt_pkattvals = (char **) palloc(tgt_nitems * sizeof(char *));
	ptr = ARR_DATA_PTR(tgt_pkattvals_arry);
	for (i = 0; i < tgt_nitems; i++)
	{
		tgt_pkattvals[i] = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(ptr)));
		ptr = att_addlength(ptr, typlen, PointerGetDatum(ptr));
		ptr = (char *) att_align(ptr, typalign);
	}

	/*
	 * Prep work is finally done. Go get the SQL string.
	 */
	sql = get_sql_update(relid, pkattnums, pknumatts, src_pkattvals, tgt_pkattvals);

	/*
	 * And send it
	 */
	PG_RETURN_TEXT_P(GET_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)
{
	PG_RETURN_TEXT_P(GET_TEXT(debug_query_string));
}


/*************************************************************
 * internal functions
 */


/*
 * get_pkey_attnames
 *
 * Get the primary key attnames for the given relation.
 * Return NULL, and set numatts = 0, if no primary key exists.
 */
static char **
get_pkey_attnames(Oid relid, int16 *numatts)
{
	Relation	indexRelation;
	ScanKeyData entry;
	HeapScanDesc scan;
	HeapTuple	indexTuple;
	int			i;
	char	  **result = NULL;
	Relation	rel;
	TupleDesc	tupdesc;

	/* open relation using relid, get tupdesc */
	rel = relation_open(relid, AccessShareLock);
	tupdesc = rel->rd_att;

	/* initialize numatts to 0 in case no primary key exists */
	*numatts = 0;

	/* use relid to get all related indexes */
	indexRelation = heap_openr(IndexRelationName, AccessShareLock);
	ScanKeyEntryInitialize(&entry, 0, Anum_pg_index_indrelid,
						   F_OIDEQ, ObjectIdGetDatum(relid));
	scan = heap_beginscan(indexRelation, SnapshotNow, 1, &entry);

	while ((indexTuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
	{
		Form_pg_index index = (Form_pg_index) GETSTRUCT(indexTuple);

		/* we're only interested if it is the primary key */
		if (index->indisprimary == TRUE)
		{
			i = 0;
			while (index->indkey[i++] != 0)
				(*numatts)++;

			if (*numatts > 0)
			{
				result = (char **) palloc(*numatts * sizeof(char *));

				for (i = 0; i < *numatts; i++)
					result[i] = SPI_fname(tupdesc, index->indkey[i]);
			}
			break;
		}
	}
	heap_endscan(scan);
	heap_close(indexRelation, AccessShareLock);
	relation_close(rel, AccessShareLock);

	return result;
}

static char *
get_sql_insert(Oid relid, int16 *pkattnums, int16 pknumatts, char **src_pkattvals, char **tgt_pkattvals)
{
	Relation	rel;
	char	   *relname;
	HeapTuple	tuple;
	TupleDesc	tupdesc;
	int			natts;
	StringInfo	str = makeStringInfo();
	char	   *sql;
	char	   *val;
	int16		key;
	int			i;
	bool		needComma;

	/* get relation name including any needed schema prefix and quoting */
	relname = generate_relation_name(relid);

	/*
	 * Open relation using relid
	 */
	rel = relation_open(relid, AccessShareLock);
	tupdesc = rel->rd_att;
	natts = tupdesc->natts;

	tuple = get_tuple_of_interest(relid, pkattnums, pknumatts, src_pkattvals);
	if (!tuple)
		ereport(ERROR,
				(errcode(ERRCODE_CARDINALITY_VIOLATION),
				 errmsg("source row not found")));

	appendStringInfo(str, "INSERT INTO %s(", relname);

	needComma = false;
	for (i = 0; i < natts; i++)
	{
		if (tupdesc->attrs[i]->attisdropped)
			continue;

		if (needComma)
			appendStringInfo(str, ",");

		appendStringInfo(str, "%s",
				  quote_ident_cstr(NameStr(tupdesc->attrs[i]->attname)));
		needComma = true;
	}

	appendStringInfo(str, ") VALUES(");

	/*
	 * remember attvals are 1 based
	 */
	needComma = false;
	for (i = 0; i < natts; i++)
	{
		if (tupdesc->attrs[i]->attisdropped)
			continue;

		if (needComma)
			appendStringInfo(str, ",");

		if (tgt_pkattvals != NULL)
			key = get_attnum_pk_pos(pkattnums, pknumatts, i + 1);
		else
			key = -1;

		if (key > -1)
			val = pstrdup(tgt_pkattvals[key]);
		else
			val = SPI_getvalue(tuple, tupdesc, i + 1);

		if (val != NULL)
		{
			appendStringInfo(str, "%s", quote_literal_cstr(val));
			pfree(val);
		}
		else
			appendStringInfo(str, "NULL");
		needComma = true;
	}
	appendStringInfo(str, ")");

	sql = pstrdup(str->data);
	pfree(str->data);
	pfree(str);
	relation_close(rel, AccessShareLock);

	return (sql);
}

static char *
get_sql_delete(Oid relid, int16 *pkattnums, int16 pknumatts, char **tgt_pkattvals)
{
	Relation	rel;
	char	   *relname;
	TupleDesc	tupdesc;
	int			natts;
	StringInfo	str = makeStringInfo();
	char	   *sql;
	char	   *val = NULL;
	int			i;

	/* get relation name including any needed schema prefix and quoting */
	relname = generate_relation_name(relid);

	/*
	 * Open relation using relid
	 */
	rel = relation_open(relid, AccessShareLock);
	tupdesc = rel->rd_att;
	natts = tupdesc->natts;

	appendStringInfo(str, "DELETE FROM %s WHERE ", relname);
	for (i = 0; i < pknumatts; i++)
	{
		int16		pkattnum = pkattnums[i];

		if (i > 0)
			appendStringInfo(str, " AND ");

		appendStringInfo(str, "%s",
		quote_ident_cstr(NameStr(tupdesc->attrs[pkattnum - 1]->attname)));

		if (tgt_pkattvals != NULL)
			val = pstrdup(tgt_pkattvals[i]);
		else
			/* internal error */
			elog(ERROR, "target key array must not be NULL");

		if (val != NULL)
		{
			appendStringInfo(str, " = %s", quote_literal_cstr(val));
			pfree(val);
		}
		else
			appendStringInfo(str, " IS NULL");
	}

	sql = pstrdup(str->data);
	pfree(str->data);
	pfree(str);
	relation_close(rel, AccessShareLock);

	return (sql);
}

static char *
get_sql_update(Oid relid, int16 *pkattnums, int16 pknumatts, char **src_pkattvals, char **tgt_pkattvals)
{
	Relation	rel;
	char	   *relname;
	HeapTuple	tuple;
	TupleDesc	tupdesc;
	int			natts;
	StringInfo	str = makeStringInfo();
	char	   *sql;
	char	   *val;
	int16		key;
	int			i;
	bool		needComma;

	/* get relation name including any needed schema prefix and quoting */
	relname = generate_relation_name(relid);

	/*
	 * Open relation using relid
	 */
	rel = relation_open(relid, AccessShareLock);
	tupdesc = rel->rd_att;
	natts = tupdesc->natts;

	tuple = get_tuple_of_interest(relid, pkattnums, pknumatts, src_pkattvals);
	if (!tuple)
		ereport(ERROR,
				(errcode(ERRCODE_CARDINALITY_VIOLATION),
				 errmsg("source row not found")));

	appendStringInfo(str, "UPDATE %s SET ", relname);

	needComma = false;
	for (i = 0; i < natts; i++)
	{
		if (tupdesc->attrs[i]->attisdropped)
			continue;

		if (needComma)
			appendStringInfo(str, ", ");

		appendStringInfo(str, "%s = ",
				  quote_ident_cstr(NameStr(tupdesc->attrs[i]->attname)));

		if (tgt_pkattvals != NULL)
			key = get_attnum_pk_pos(pkattnums, pknumatts, i + 1);
		else
			key = -1;

		if (key > -1)
			val = pstrdup(tgt_pkattvals[key]);
		else
			val = SPI_getvalue(tuple, tupdesc, i + 1);

		if (val != NULL)
		{
			appendStringInfo(str, "%s", quote_literal_cstr(val));
			pfree(val);
		}
		else
			appendStringInfo(str, "NULL");
		needComma = true;
	}

	appendStringInfo(str, " WHERE ");

	for (i = 0; i < pknumatts; i++)
	{
		int16		pkattnum = pkattnums[i];

		if (i > 0)
			appendStringInfo(str, " AND ");

		appendStringInfo(str, "%s",
		quote_ident_cstr(NameStr(tupdesc->attrs[pkattnum - 1]->attname)));

		if (tgt_pkattvals != NULL)
			val = pstrdup(tgt_pkattvals[i]);
		else
			val = SPI_getvalue(tuple, tupdesc, pkattnum);

		if (val != NULL)
		{
			appendStringInfo(str, " = %s", quote_literal_cstr(val));
			pfree(val);
		}
		else
			appendStringInfo(str, " IS NULL");
	}

	sql = pstrdup(str->data);
	pfree(str->data);
	pfree(str);
	relation_close(rel, AccessShareLock);

	return (sql);
}

/*
 * Return a properly quoted literal value.
 * Uses quote_literal in quote.c
 */
static char *
quote_literal_cstr(char *rawstr)
{
	text	   *rawstr_text;
	text	   *result_text;
	char	   *result;

	rawstr_text = DatumGetTextP(DirectFunctionCall1(textin, CStringGetDatum(rawstr)));
	result_text = DatumGetTextP(DirectFunctionCall1(quote_literal, PointerGetDatum(rawstr_text)));
	result = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(result_text)));

	return result;
}

/*
 * 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 = DatumGetTextP(DirectFunctionCall1(textin, CStringGetDatum(rawstr)));
	result_text = DatumGetTextP(DirectFunctionCall1(quote_ident, PointerGetDatum(rawstr_text)));
	result = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(result_text)));

	return result;
}

static int16
get_attnum_pk_pos(int16 *pkattnums, int16 pknumatts, int16 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(Oid relid, int16 *pkattnums, int16 pknumatts, char **src_pkattvals)
{
	Relation	rel;
	char	   *relname;
	TupleDesc	tupdesc;
	StringInfo	str = makeStringInfo();
	char	   *sql = NULL;
	int			ret;
	HeapTuple	tuple;
	int			i;
	char	   *val = NULL;

	/* get relation name including any needed schema prefix and quoting */
	relname = generate_relation_name(relid);

	/*
	 * Open relation using relid
	 */
	rel = relation_open(relid, AccessShareLock);
	tupdesc = CreateTupleDescCopy(rel->rd_att);
	relation_close(rel, AccessShareLock);

	/*
	 * Connect to SPI manager
	 */
	if ((ret = SPI_connect()) < 0)
		/* internal error */
		elog(ERROR, "SPI connect failure - returned %d", ret);

	/*
	 * Build sql statement to look up tuple of interest Use src_pkattvals
	 * as the criteria.
	 */
	appendStringInfo(str, "SELECT * FROM %s WHERE ", relname);

	for (i = 0; i < pknumatts; i++)
	{
		int16		pkattnum = pkattnums[i];

		if (i > 0)
			appendStringInfo(str, " AND ");

		appendStringInfo(str, "%s",
		quote_ident_cstr(NameStr(tupdesc->attrs[pkattnum - 1]->attname)));

		val = pstrdup(src_pkattvals[i]);
		if (val != NULL)
		{
			appendStringInfo(str, " = %s", quote_literal_cstr(val));
			pfree(val);
		}
		else
			appendStringInfo(str, " IS NULL");
	}

	sql = pstrdup(str->data);
	pfree(str->data);
	pfree(str);

	/*
	 * Retrieve the desired tuple
	 */
	ret = SPI_exec(sql, 0);
	pfree(sql);

	/*
	 * 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]);

		return tuple;
	}
	else
	{
		/*
		 * no qualifying tuples
		 */
		return NULL;
	}

	/*
	 * never reached, but keep compiler quiet
	 */
	return NULL;
}

static Oid
get_relid_from_relname(text *relname_text)
{
	RangeVar   *relvar;
	Relation	rel;
	Oid			relid;

	relvar = makeRangeVarFromNameList(textToQualifiedNameList(relname_text, "get_relid_from_relname"));
	rel = heap_openrv(relvar, AccessShareLock);
	relid = RelationGetRelid(rel);
	relation_close(rel, AccessShareLock);

	return relid;
}

static TupleDesc
pgresultGetTupleDesc(PGresult *res)
{
	int			natts;
	AttrNumber	attnum;
	TupleDesc	desc;
	char	   *attname;
	int32		atttypmod;
	int			attdim;
	bool		attisset;
	Oid			atttypid;
	int			i;

	/*
	 * allocate a new tuple descriptor
	 */
	natts = PQnfields(res);
	if (natts < 1)
		/* shouldn't happen */
		elog(ERROR, "cannot create a description for empty results");

	desc = CreateTemplateTupleDesc(natts, false);

	attnum = 0;

	for (i = 0; i < natts; i++)
	{
		/*
		 * for each field, get the name and type information from the
		 * query result and have TupleDescInitEntry fill in the attribute
		 * information we need.
		 */
		attnum++;

		attname = PQfname(res, i);
		atttypid = PQftype(res, i);
		atttypmod = PQfmod(res, i);

		if (PQfsize(res, i) != get_typlen(atttypid))
			ereport(ERROR,
					(errcode(ERRCODE_MOST_SPECIFIC_TYPE_MISMATCH),
					 errmsg("field size mismatch"),
					 errdetail("Size of remote field \"%s\" does not match " \
								"size of local type \"%s\".", attname,
								format_type_with_typemod(atttypid,
														 atttypmod))));

		attdim = 0;
		attisset = false;

		TupleDescInitEntry(desc, attnum, attname, atttypid,
						   atttypmod, attdim, attisset);
	}

	return desc;
}

/*
 * generate_relation_name - copied from ruleutils.c
 *		Compute the name to display for a relation specified by OID
 *
 * The result includes all necessary quoting and schema-prefixing.
 */
static char *
generate_relation_name(Oid relid)
{
	HeapTuple	tp;
	Form_pg_class reltup;
	char	   *nspname;
	char	   *result;

	tp = SearchSysCache(RELOID,
						ObjectIdGetDatum(relid),
						0, 0, 0);
	if (!HeapTupleIsValid(tp))
		elog(ERROR, "cache lookup failed for relation %u", relid);

	reltup = (Form_pg_class) GETSTRUCT(tp);

	/* Qualify the name if not visible in search path */
	if (RelationIsVisible(relid))
		nspname = NULL;
	else
		nspname = get_namespace_name(reltup->relnamespace);

	result = quote_qualified_identifier(nspname, NameStr(reltup->relname));

	ReleaseSysCache(tp);

	return result;
}


static remoteConn *
getConnectionByName(const char *name)
{
	remoteConnHashEnt  *hentry;
	char				key[NAMEDATALEN];

	if(!remoteConnHash)
		remoteConnHash=createConnHash();

	MemSet(key, 0, NAMEDATALEN);
	snprintf(key, NAMEDATALEN - 1, "%s", name);
	hentry = (remoteConnHashEnt*) hash_search(remoteConnHash,
											  key, HASH_FIND, NULL);

	if(hentry)
		return(hentry->rcon);

	return(NULL);
}

static HTAB *
createConnHash(void)
{
	HASHCTL	ctl;
	HTAB   *ptr;

	ctl.keysize = NAMEDATALEN;
	ctl.entrysize = sizeof(remoteConnHashEnt);

	ptr=hash_create("Remote Con hash", NUMCONN, &ctl, HASH_ELEM);

	if(!ptr)
		ereport(ERROR,
				(errcode(ERRCODE_OUT_OF_MEMORY),
				 errmsg("out of memory")));

	return(ptr);
}

static void
createNewConnection(const char *name, remoteConn *con)
{
	remoteConnHashEnt  *hentry;
	bool				found;
	char				key[NAMEDATALEN];

	if(!remoteConnHash)
		remoteConnHash = createConnHash();

	MemSet(key, 0, NAMEDATALEN);
	snprintf(key, NAMEDATALEN - 1, "%s", name);
	hentry = (remoteConnHashEnt *) hash_search(remoteConnHash, key,
											   HASH_ENTER, &found);

	if(!hentry)
		ereport(ERROR,
				(errcode(ERRCODE_OUT_OF_MEMORY),
				 errmsg("out of memory")));

	if(found)
		ereport(ERROR,
				(errcode(ERRCODE_DUPLICATE_OBJECT),
				 errmsg("duplicate connection name")));

	hentry->rcon = con;
	strncpy(hentry->name, name, NAMEDATALEN - 1);
}

static void
deleteConnection(const char *name)
{
	remoteConnHashEnt  *hentry;
	bool				found;
	char				key[NAMEDATALEN];

	if(!remoteConnHash)
		remoteConnHash=createConnHash();

	MemSet(key, 0, NAMEDATALEN);
	snprintf(key, NAMEDATALEN - 1, "%s", name);

	hentry = (remoteConnHashEnt *) hash_search(remoteConnHash,
											   key, HASH_REMOVE, &found);

	if(!hentry)
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_OBJECT),
				 errmsg("undefined connection name")));

}