Allow postgres_fdw to ship extension funcs/operators for remote execution.

The user can whitelist specified extension(s) in the foreign server's
options, whereupon we will treat immutable functions and operators of those
extensions as candidates to be sent for remote execution.

Whitelisting an extension in this way basically promises that the extension
exists on the remote server and behaves compatibly with the local instance.
We have no way to prove that formally, so we have to rely on the user to
get it right.  But this seems like something that people can usually get
right in practice.

We might in future allow functions and operators to be whitelisted
individually, but extension granularity is a very convenient special case,
so it got done first.

The patch as-committed lacks any regression tests, which is unfortunate,
but introducing dependencies on other extensions for testing purposes
would break "make installcheck" scenarios, which is worse.  I have some
ideas about klugy ways around that, but it seems like material for a
separate patch.  For the moment, leave the problem open.

Paul Ramsey, hacked up a bit more by me

Author: tglsfdc

contrib/postgres_fdw/Makefile

@@ -1,7 +1,7 @@
 # contrib/postgres_fdw/Makefile
 
 MODULE_big = postgres_fdw
-OBJS = postgres_fdw.o option.o deparse.o connection.o $(WIN32RES)
+OBJS = postgres_fdw.o option.o deparse.o connection.o shippable.o $(WIN32RES)
 PGFILEDESC = "postgres_fdw - foreign data wrapper for PostgreSQL"
 
 PG_CPPFLAGS = -I$(libpq_srcdir)

contrib/postgres_fdw/deparse.c

@@ -38,7 +38,6 @@
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "access/sysattr.h"
-#include "access/transam.h"
 #include "catalog/pg_collation.h"
 #include "catalog/pg_namespace.h"
 #include "catalog/pg_operator.h"
@@ -102,7 +101,7 @@ typedef struct deparse_expr_cxt
 static bool foreign_expr_walker(Node *node,
 					foreign_glob_cxt *glob_cxt,
 					foreign_loc_cxt *outer_cxt);
-static bool is_builtin(Oid procid);
+static char *deparse_type_name(Oid type_oid, int32 typemod);
 
 /*
  * Functions to construct string representation of a node tree.
@@ -220,18 +219,20 @@ is_foreign_expr(PlannerInfo *root,
  * In addition, *outer_cxt is updated with collation information.
  *
  * We must check that the expression contains only node types we can deparse,
- * that all types/functions/operators are safe to send (which we approximate
- * as being built-in), and that all collations used in the expression derive
- * from Vars of the foreign table.  Because of the latter, the logic is
- * pretty close to assign_collations_walker() in parse_collate.c, though we
- * can assume here that the given expression is valid.
+ * that all types/functions/operators are safe to send (they are "shippable"),
+ * and that all collations used in the expression derive from Vars of the
+ * foreign table.  Because of the latter, the logic is pretty close to
+ * assign_collations_walker() in parse_collate.c, though we can assume here
+ * that the given expression is valid.  Note function mutability is not
+ * currently considered here.
  */
 static bool
 foreign_expr_walker(Node *node,
 					foreign_glob_cxt *glob_cxt,
 					foreign_loc_cxt *outer_cxt)
 {
 	bool		check_type = true;
+	PgFdwRelationInfo *fpinfo;
 	foreign_loc_cxt inner_cxt;
 	Oid			collation;
 	FDWCollateState state;
@@ -240,6 +241,9 @@ foreign_expr_walker(Node *node,
 	if (node == NULL)
 		return true;
 
+	/* May need server info from baserel's fdw_private struct */
+	fpinfo = (PgFdwRelationInfo *) (glob_cxt->foreignrel->fdw_private);
+
 	/* Set up inner_cxt for possible recursion to child nodes */
 	inner_cxt.collation = InvalidOid;
 	inner_cxt.state = FDW_COLLATE_NONE;
@@ -377,11 +381,11 @@ foreign_expr_walker(Node *node,
 				FuncExpr   *fe = (FuncExpr *) node;
 
 				/*
-				 * If function used by the expression is not built-in, it
+				 * If function used by the expression is not shippable, it
 				 * can't be sent to remote because it might have incompatible
 				 * semantics on remote side.
 				 */
-				if (!is_builtin(fe->funcid))
+				if (!is_shippable(fe->funcid, ProcedureRelationId, fpinfo))
 					return false;
 
 				/*
@@ -425,11 +429,11 @@ foreign_expr_walker(Node *node,
 				OpExpr	   *oe = (OpExpr *) node;
 
 				/*
-				 * Similarly, only built-in operators can be sent to remote.
-				 * (If the operator is, surely its underlying function is
-				 * too.)
+				 * Similarly, only shippable operators can be sent to remote.
+				 * (If the operator is shippable, we assume its underlying
+				 * function is too.)
 				 */
-				if (!is_builtin(oe->opno))
+				if (!is_shippable(oe->opno, OperatorRelationId, fpinfo))
 					return false;
 
 				/*
@@ -467,9 +471,9 @@ foreign_expr_walker(Node *node,
 				ScalarArrayOpExpr *oe = (ScalarArrayOpExpr *) node;
 
 				/*
-				 * Again, only built-in operators can be sent to remote.
+				 * Again, only shippable operators can be sent to remote.
 				 */
-				if (!is_builtin(oe->opno))
+				if (!is_shippable(oe->opno, OperatorRelationId, fpinfo))
 					return false;
 
 				/*
@@ -616,10 +620,10 @@ foreign_expr_walker(Node *node,
 	}
 
 	/*
-	 * If result type of given expression is not built-in, it can't be sent to
-	 * remote because it might have incompatible semantics on remote side.
+	 * If result type of given expression is not shippable, it can't be sent
+	 * to remote because it might have incompatible semantics on remote side.
 	 */
-	if (check_type && !is_builtin(exprType(node)))
+	if (check_type && !is_shippable(exprType(node), TypeRelationId, fpinfo))
 		return false;
 
 	/*
@@ -672,27 +676,23 @@ foreign_expr_walker(Node *node,
 }
 
 /*
- * Return true if given object is one of PostgreSQL's built-in objects.
- *
- * We use FirstBootstrapObjectId as the cutoff, so that we only consider
- * objects with hand-assigned OIDs to be "built in", not for instance any
- * function or type defined in the information_schema.
+ * Convert type OID + typmod info into a type name we can ship to the remote
+ * server.  Someplace else had better have verified that this type name is
+ * expected to be known on the remote end.
  *
- * Our constraints for dealing with types are tighter than they are for
- * functions or operators: we want to accept only types that are in pg_catalog,
- * else format_type might incorrectly fail to schema-qualify their names.
- * (This could be fixed with some changes to format_type, but for now there's
- * no need.)  Thus we must exclude information_schema types.
- *
- * XXX there is a problem with this, which is that the set of built-in
- * objects expands over time.  Something that is built-in to us might not
- * be known to the remote server, if it's of an older version.  But keeping
- * track of that would be a huge exercise.
+ * This is almost just format_type_with_typemod(), except that if left to its
+ * own devices, that function will make schema-qualification decisions based
+ * on the local search_path, which is wrong.  We must schema-qualify all
+ * type names that are not in pg_catalog.  We assume here that built-in types
+ * are all in pg_catalog and need not be qualified; otherwise, qualify.
  */
-static bool
-is_builtin(Oid oid)
+static char *
+deparse_type_name(Oid type_oid, int32 typemod)
 {
-	return (oid < FirstBootstrapObjectId);
+	if (is_builtin(type_oid))
+		return format_type_with_typemod(type_oid, typemod);
+	else
+		return format_type_with_typemod_qualified(type_oid, typemod);
 }
 
 
@@ -1358,8 +1358,8 @@ deparseConst(Const *node, deparse_expr_cxt *context)
 	{
 		appendStringInfoString(buf, "NULL");
 		appendStringInfo(buf, "::%s",
-						 format_type_with_typemod(node->consttype,
-												  node->consttypmod));
+						 deparse_type_name(node->consttype,
+										   node->consttypmod));
 		return;
 	}
 
@@ -1432,8 +1432,8 @@ deparseConst(Const *node, deparse_expr_cxt *context)
 	}
 	if (needlabel)
 		appendStringInfo(buf, "::%s",
-						 format_type_with_typemod(node->consttype,
-												  node->consttypmod));
+						 deparse_type_name(node->consttype,
+										   node->consttypmod));
 }
 
 /*
@@ -1558,7 +1558,7 @@ deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context)
 
 		deparseExpr((Expr *) linitial(node->args), context);
 		appendStringInfo(buf, "::%s",
-						 format_type_with_typemod(rettype, coercedTypmod));
+						 deparse_type_name(rettype, coercedTypmod));
 		return;
 	}
 
@@ -1753,8 +1753,8 @@ deparseRelabelType(RelabelType *node, deparse_expr_cxt *context)
 	deparseExpr(node->arg, context);
 	if (node->relabelformat != COERCE_IMPLICIT_CAST)
 		appendStringInfo(context->buf, "::%s",
-						 format_type_with_typemod(node->resulttype,
-												  node->resulttypmod));
+						 deparse_type_name(node->resulttype,
+										   node->resulttypmod));
 }
 
 /*
@@ -1834,7 +1834,7 @@ deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context)
 	/* If the array is empty, we need an explicit cast to the array type. */
 	if (node->elements == NIL)
 		appendStringInfo(buf, "::%s",
-						 format_type_with_typemod(node->array_typeid, -1));
+						 deparse_type_name(node->array_typeid, -1));
 }
 
 /*
@@ -1850,7 +1850,7 @@ printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
 				 deparse_expr_cxt *context)
 {
 	StringInfo	buf = context->buf;
-	char	   *ptypename = format_type_with_typemod(paramtype, paramtypmod);
+	char	   *ptypename = deparse_type_name(paramtype, paramtypmod);
 
 	appendStringInfo(buf, "$%d::%s", paramindex, ptypename);
 }
@@ -1876,7 +1876,7 @@ printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
 					   deparse_expr_cxt *context)
 {
 	StringInfo	buf = context->buf;
-	char	   *ptypename = format_type_with_typemod(paramtype, paramtypmod);
+	char	   *ptypename = deparse_type_name(paramtype, paramtypmod);
 
 	appendStringInfo(buf, "((SELECT null::%s)::%s)", ptypename, ptypename);
 }
@@ -1890,10 +1890,10 @@ void
 appendOrderByClause(StringInfo buf, PlannerInfo *root, RelOptInfo *baserel,
 					List *pathkeys)
 {
-	ListCell			*lcell;
-	deparse_expr_cxt	context;
-	int					nestlevel;
-	char				*delim = " ";
+	ListCell   *lcell;
+	deparse_expr_cxt context;
+	int			nestlevel;
+	char	   *delim = " ";
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -1907,8 +1907,8 @@ appendOrderByClause(StringInfo buf, PlannerInfo *root, RelOptInfo *baserel,
 	appendStringInfo(buf, " ORDER BY");
 	foreach(lcell, pathkeys)
 	{
-		PathKey				*pathkey = lfirst(lcell);
-		Expr				*em_expr;
+		PathKey    *pathkey = lfirst(lcell);
+		Expr	   *em_expr;
 
 		em_expr = find_em_expr_for_rel(pathkey->pk_eclass, baserel);
 		Assert(em_expr != NULL);

contrib/postgres_fdw/option.c

@@ -19,6 +19,8 @@
 #include "catalog/pg_foreign_table.h"
 #include "catalog/pg_user_mapping.h"
 #include "commands/defrem.h"
+#include "commands/extension.h"
+#include "utils/builtins.h"
 
 
 /*
@@ -124,6 +126,11 @@ postgres_fdw_validator(PG_FUNCTION_ARGS)
 						 errmsg("%s requires a non-negative numeric value",
 								def->defname)));
 		}
+		else if (strcmp(def->defname, "extensions") == 0)
+		{
+			/* check list syntax, warn about uninstalled extensions */
+			(void) ExtractExtensionList(defGetString(def), true);
+		}
 	}
 
 	PG_RETURN_VOID();
@@ -150,6 +157,8 @@ InitPgFdwOptions(void)
 		/* cost factors */
 		{"fdw_startup_cost", ForeignServerRelationId, false},
 		{"fdw_tuple_cost", ForeignServerRelationId, false},
+		/* shippable extensions */
+		{"extensions", ForeignServerRelationId, false},
 		/* updatable is available on both server and table */
 		{"updatable", ForeignServerRelationId, false},
 		{"updatable", ForeignTableRelationId, false},
@@ -293,3 +302,48 @@ ExtractConnectionOptions(List *defelems, const char **keywords,
 	}
 	return i;
 }
+
+/*
+ * Parse a comma-separated string and return a List of the OIDs of the
+ * extensions named in the string.  If any names in the list cannot be
+ * found, report a warning if warnOnMissing is true, else just silently
+ * ignore them.
+ */
+List *
+ExtractExtensionList(const char *extensionsString, bool warnOnMissing)
+{
+	List	   *extensionOids = NIL;
+	List	   *extlist;
+	ListCell   *lc;
+
+	/* SplitIdentifierString scribbles on its input, so pstrdup first */
+	if (!SplitIdentifierString(pstrdup(extensionsString), ',', &extlist))
+	{
+		/* syntax error in name list */
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("parameter \"%s\" must be a list of extension names",
+						"extensions")));
+	}
+
+	foreach(lc, extlist)
+	{
+		const char *extension_name = (const char *) lfirst(lc);
+		Oid			extension_oid = get_extension_oid(extension_name, true);
+
+		if (OidIsValid(extension_oid))
+		{
+			extensionOids = lappend_oid(extensionOids, extension_oid);
+		}
+		else if (warnOnMissing)
+		{
+			ereport(WARNING,
+					(errcode(ERRCODE_UNDEFINED_OBJECT),
+					 errmsg("extension \"%s\" is not installed",
+							extension_name)));
+		}
+	}
+
+	list_free(extlist);
+	return extensionOids;
+}

contrib/postgres_fdw/postgres_fdw.c

@@ -50,40 +50,6 @@ PG_MODULE_MAGIC;
 /* If no remote estimates, assume a sort costs 20% extra */
 #define DEFAULT_FDW_SORT_MULTIPLIER 1.2
 
-/*
- * FDW-specific planner information kept in RelOptInfo.fdw_private for a
- * foreign table.  This information is collected by postgresGetForeignRelSize.
- */
-typedef struct PgFdwRelationInfo
-{
-	/* baserestrictinfo clauses, broken down into safe and unsafe subsets. */
-	List	   *remote_conds;
-	List	   *local_conds;
-
-	/* Bitmap of attr numbers we need to fetch from the remote server. */
-	Bitmapset  *attrs_used;
-
-	/* Cost and selectivity of local_conds. */
-	QualCost	local_conds_cost;
-	Selectivity local_conds_sel;
-
-	/* Estimated size and cost for a scan with baserestrictinfo quals. */
-	double		rows;
-	int			width;
-	Cost		startup_cost;
-	Cost		total_cost;
-
-	/* Options extracted from catalogs. */
-	bool		use_remote_estimate;
-	Cost		fdw_startup_cost;
-	Cost		fdw_tuple_cost;
-
-	/* Cached catalog information. */
-	ForeignTable *table;
-	ForeignServer *server;
-	UserMapping *user;			/* only set in use_remote_estimate mode */
-} PgFdwRelationInfo;
-
 /*
  * Indexes of FDW-private information stored in fdw_private lists.
  *
@@ -409,6 +375,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 	fpinfo->use_remote_estimate = false;
 	fpinfo->fdw_startup_cost = DEFAULT_FDW_STARTUP_COST;
 	fpinfo->fdw_tuple_cost = DEFAULT_FDW_TUPLE_COST;
+	fpinfo->shippable_extensions = NIL;
 
 	foreach(lc, fpinfo->server->options)
 	{
@@ -420,6 +387,9 @@ postgresGetForeignRelSize(PlannerInfo *root,
 			fpinfo->fdw_startup_cost = strtod(defGetString(def), NULL);
 		else if (strcmp(def->defname, "fdw_tuple_cost") == 0)
 			fpinfo->fdw_tuple_cost = strtod(defGetString(def), NULL);
+		else if (strcmp(def->defname, "extensions") == 0)
+			fpinfo->shippable_extensions =
+				ExtractExtensionList(defGetString(def), false);
 	}
 	foreach(lc, fpinfo->table->options)
 	{