Revise FDW planning API, again.

Further reflection shows that a single callback isn't very workable if we
desire to let FDWs generate multiple Paths, because that forces the FDW to
do all work necessary to generate a valid Plan node for each Path.  Instead
split the former PlanForeignScan API into three steps: GetForeignRelSize,
GetForeignPaths, GetForeignPlan.  We had already bit the bullet of breaking
the 9.1 FDW API for 9.2, so this shouldn't cause very much additional pain,
and it's substantially more flexible for complex FDWs.

Add an fdw_private field to RelOptInfo so that the new functions can save
state there rather than possibly having to recalculate information two or
three times.

In addition, we'd not thought through what would be needed to allow an FDW
to set up subexpressions of its choice for runtime execution.  We could
treat ForeignScan.fdw_private as an executable expression but that seems
likely to break existing FDWs unnecessarily (in particular, it would
restrict the set of node types allowable in fdw_private to those supported
by expression_tree_walker).  Instead, invent a separate field fdw_exprs
which will receive the postprocessing appropriate for expression trees.
(One field is enough since it can be a list of expressions; also, we assume
the corresponding expression state tree(s) will be held within fdw_state,
so we don't need to add anything to ForeignScanState.)

Per review of Hanada Shigeru's pgsql_fdw patch.  We may need to tweak this
further as we continue to work on that patch, but to me it feels a lot
closer to being right now.

contrib/file_fdw/file_fdw.c

@@ -26,6 +26,8 @@
 #include "nodes/makefuncs.h"
 #include "optimizer/cost.h"
 #include "optimizer/pathnode.h"
+#include "optimizer/planmain.h"
+#include "optimizer/restrictinfo.h"
 #include "utils/rel.h"
 
 PG_MODULE_MAGIC;
@@ -48,7 +50,7 @@ struct FileFdwOption
  * Note: If you are adding new option for user mapping, you need to modify
  * fileGetOptions(), which currently doesn't bother to look at user mappings.
  */
-static struct FileFdwOption valid_options[] = {
+static const struct FileFdwOption valid_options[] = {
 	/* File options */
 	{"filename", ForeignTableRelationId},
 
@@ -71,6 +73,17 @@ static struct FileFdwOption valid_options[] = {
 	{NULL, InvalidOid}
 };
 
+/*
+ * FDW-specific information for RelOptInfo.fdw_private.
+ */
+typedef struct FileFdwPlanState
+{
+	char	   *filename;		/* file to read */
+	List	   *options;		/* merged COPY options, excluding filename */
+	BlockNumber pages;			/* estimate of file's physical size */
+	double		ntuples;		/* estimate of number of rows in file */
+} FileFdwPlanState;
+
 /*
  * FDW-specific information for ForeignScanState.fdw_state.
  */
@@ -93,9 +106,18 @@ PG_FUNCTION_INFO_V1(file_fdw_validator);
 /*
  * FDW callback routines
  */
-static void filePlanForeignScan(Oid foreigntableid,
-					PlannerInfo *root,
-					RelOptInfo *baserel);
+static void fileGetForeignRelSize(PlannerInfo *root,
+								  RelOptInfo *baserel,
+								  Oid foreigntableid);
+static void fileGetForeignPaths(PlannerInfo *root,
+								RelOptInfo *baserel,
+								Oid foreigntableid);
+static ForeignScan *fileGetForeignPlan(PlannerInfo *root,
+									   RelOptInfo *baserel,
+									   Oid foreigntableid,
+									   ForeignPath *best_path,
+									   List *tlist,
+									   List *scan_clauses);
 static void fileExplainForeignScan(ForeignScanState *node, ExplainState *es);
 static void fileBeginForeignScan(ForeignScanState *node, int eflags);
 static TupleTableSlot *fileIterateForeignScan(ForeignScanState *node);
@@ -109,8 +131,10 @@ static bool is_valid_option(const char *option, Oid context);
 static void fileGetOptions(Oid foreigntableid,
 			   char **filename, List **other_options);
 static List *get_file_fdw_attribute_options(Oid relid);
+static void estimate_size(PlannerInfo *root, RelOptInfo *baserel,
+			  FileFdwPlanState *fdw_private);
 static void estimate_costs(PlannerInfo *root, RelOptInfo *baserel,
-			   const char *filename,
+			   FileFdwPlanState *fdw_private,
 			   Cost *startup_cost, Cost *total_cost);
 
 
@@ -123,7 +147,9 @@ file_fdw_handler(PG_FUNCTION_ARGS)
 {
 	FdwRoutine *fdwroutine = makeNode(FdwRoutine);
 
-	fdwroutine->PlanForeignScan = filePlanForeignScan;
+	fdwroutine->GetForeignRelSize = fileGetForeignRelSize;
+	fdwroutine->GetForeignPaths = fileGetForeignPaths;
+	fdwroutine->GetForeignPlan = fileGetForeignPlan;
 	fdwroutine->ExplainForeignScan = fileExplainForeignScan;
 	fdwroutine->BeginForeignScan = fileBeginForeignScan;
 	fdwroutine->IterateForeignScan = fileIterateForeignScan;
@@ -177,7 +203,7 @@ file_fdw_validator(PG_FUNCTION_ARGS)
 
 		if (!is_valid_option(def->defname, catalog))
 		{
-			struct FileFdwOption *opt;
+			const struct FileFdwOption *opt;
 			StringInfoData buf;
 
 			/*
@@ -249,7 +275,7 @@ file_fdw_validator(PG_FUNCTION_ARGS)
 static bool
 is_valid_option(const char *option, Oid context)
 {
-	struct FileFdwOption *opt;
+	const struct FileFdwOption *opt;
 
 	for (opt = valid_options; opt->optname; opt++)
 	{
@@ -381,7 +407,31 @@ get_file_fdw_attribute_options(Oid relid)
 }
 
 /*
- * filePlanForeignScan
+ * fileGetForeignRelSize
+ *		Obtain relation size estimates for a foreign table
+ */
+static void
+fileGetForeignRelSize(PlannerInfo *root,
+					  RelOptInfo *baserel,
+					  Oid foreigntableid)
+{
+	FileFdwPlanState *fdw_private;
+
+	/*
+	 * Fetch options.  We only need filename at this point, but we might
+	 * as well get everything and not need to re-fetch it later in planning.
+	 */
+	fdw_private = (FileFdwPlanState *) palloc(sizeof(FileFdwPlanState));
+	fileGetOptions(foreigntableid,
+				   &fdw_private->filename, &fdw_private->options);
+	baserel->fdw_private = (void *) fdw_private;
+
+	/* Estimate relation size */
+	estimate_size(root, baserel, fdw_private);
+}
+
+/*
+ * fileGetForeignPaths
  *		Create possible access paths for a scan on the foreign table
  *
  *		Currently we don't support any push-down feature, so there is only one
@@ -389,20 +439,16 @@ get_file_fdw_attribute_options(Oid relid)
  *		the data file.
  */
 static void
-filePlanForeignScan(Oid foreigntableid,
-					PlannerInfo *root,
-					RelOptInfo *baserel)
+fileGetForeignPaths(PlannerInfo *root,
+					RelOptInfo *baserel,
+					Oid foreigntableid)
 {
-	char	   *filename;
-	List	   *options;
+	FileFdwPlanState *fdw_private = (FileFdwPlanState *) baserel->fdw_private;
 	Cost		startup_cost;
 	Cost		total_cost;
 
-	/* Fetch options --- we only need filename at this point */
-	fileGetOptions(foreigntableid, &filename, &options);
-
-	/* Estimate costs and update baserel->rows */
-	estimate_costs(root, baserel, filename,
+	/* Estimate costs */
+	estimate_costs(root, baserel, fdw_private,
 				   &startup_cost, &total_cost);
 
 	/* Create a ForeignPath node and add it as only possible path */
@@ -422,6 +468,37 @@ filePlanForeignScan(Oid foreigntableid,
 	 */
 }
 
+/*
+ * fileGetForeignPlan
+ *		Create a ForeignScan plan node for scanning the foreign table
+ */
+static ForeignScan *
+fileGetForeignPlan(PlannerInfo *root,
+				   RelOptInfo *baserel,
+				   Oid foreigntableid,
+				   ForeignPath *best_path,
+				   List *tlist,
+				   List *scan_clauses)
+{
+	Index		scan_relid = baserel->relid;
+
+	/*
+	 * We have no native ability to evaluate restriction clauses, so we just
+	 * put all the scan_clauses into the plan node's qual list for the
+	 * executor to check.  So all we have to do here is strip RestrictInfo
+	 * nodes from the clauses and ignore pseudoconstants (which will be
+	 * handled elsewhere).
+	 */
+	scan_clauses = extract_actual_clauses(scan_clauses, false);
+
+	/* Create the ForeignScan node */
+	return make_foreignscan(tlist,
+							scan_clauses,
+							scan_relid,
+							NIL, /* no expressions to evaluate */
+							NIL); /* no private state either */
+}
+
 /*
  * fileExplainForeignScan
  *		Produce extra output for EXPLAIN
@@ -568,38 +645,38 @@ fileReScanForeignScan(ForeignScanState *node)
 }
 
 /*
- * Estimate costs of scanning a foreign table.
+ * Estimate size of a foreign table.
  *
- * In addition to setting *startup_cost and *total_cost, this should
- * update baserel->rows.
+ * The main result is returned in baserel->rows.  We also set
+ * fdw_private->pages and fdw_private->ntuples for later use in the cost
+ * calculation.
  */
 static void
-estimate_costs(PlannerInfo *root, RelOptInfo *baserel,
-			   const char *filename,
-			   Cost *startup_cost, Cost *total_cost)
+estimate_size(PlannerInfo *root, RelOptInfo *baserel,
+			  FileFdwPlanState *fdw_private)
 {
 	struct stat stat_buf;
 	BlockNumber pages;
 	int			tuple_width;
 	double		ntuples;
 	double		nrows;
-	Cost		run_cost = 0;
-	Cost		cpu_per_tuple;
 
 	/*
 	 * Get size of the file.  It might not be there at plan time, though, in
 	 * which case we have to use a default estimate.
 	 */
-	if (stat(filename, &stat_buf) < 0)
+	if (stat(fdw_private->filename, &stat_buf) < 0)
 		stat_buf.st_size = 10 * BLCKSZ;
 
 	/*
-	 * Convert size to pages for use in I/O cost estimate below.
+	 * Convert size to pages for use in I/O cost estimate later.
 	 */
 	pages = (stat_buf.st_size + (BLCKSZ - 1)) / BLCKSZ;
 	if (pages < 1)
 		pages = 1;
 
+	fdw_private->pages = pages;
+
 	/*
 	 * Estimate the number of tuples in the file.  We back into this estimate
 	 * using the planner's idea of the relation width; which is bogus if not
@@ -611,6 +688,8 @@ estimate_costs(PlannerInfo *root, RelOptInfo *baserel,
 
 	ntuples = clamp_row_est((double) stat_buf.st_size / (double) tuple_width);
 
+	fdw_private->ntuples = ntuples;
+
 	/*
 	 * Now estimate the number of rows returned by the scan after applying the
 	 * baserestrictinfo quals.	This is pretty bogus too, since the planner
@@ -627,12 +706,28 @@ estimate_costs(PlannerInfo *root, RelOptInfo *baserel,
 
 	/* Save the output-rows estimate for the planner */
 	baserel->rows = nrows;
+}
+
+/*
+ * Estimate costs of scanning a foreign table.
+ *
+ * Results are returned in *startup_cost and *total_cost.
+ */
+static void
+estimate_costs(PlannerInfo *root, RelOptInfo *baserel,
+			   FileFdwPlanState *fdw_private,
+			   Cost *startup_cost, Cost *total_cost)
+{
+	BlockNumber pages = fdw_private->pages;
+	double		ntuples = fdw_private->ntuples;
+	Cost		run_cost = 0;
+	Cost		cpu_per_tuple;
 
 	/*
-	 * Now estimate costs.	We estimate costs almost the same way as
-	 * cost_seqscan(), thus assuming that I/O costs are equivalent to a
-	 * regular table file of the same size.  However, we take per-tuple CPU
-	 * costs as 10x of a seqscan, to account for the cost of parsing records.
+	 * We estimate costs almost the same way as cost_seqscan(), thus assuming
+	 * that I/O costs are equivalent to a regular table file of the same size.
+	 * However, we take per-tuple CPU costs as 10x of a seqscan, to account
+	 * for the cost of parsing records.
 	 */
 	run_cost += seq_page_cost * pages;
 

doc/src/sgml/fdwhandler.sgml

@@ -89,52 +89,92 @@
     <para>
 <programlisting>
 void
-PlanForeignScan (Oid foreigntableid,
-                 PlannerInfo *root,
-                 RelOptInfo *baserel);
+GetForeignRelSize (PlannerInfo *root,
+                   RelOptInfo *baserel,
+                   Oid foreigntableid);
 </programlisting>
 
-     Create possible access paths for a scan on a foreign table. This is
-     called when a query is planned.
+     Obtain relation size estimates for a foreign table.  This is called
+     at the beginning of planning for a query involving a foreign table.
+     <literal>root</> is the planner's global information about the query;
+     <literal>baserel</> is the planner's information about this table; and
      <literal>foreigntableid</> is the <structname>pg_class</> OID of the
-     foreign table.  <literal>root</> is the planner's global information
-     about the query, and <literal>baserel</> is the planner's information
-     about this table.
+     foreign table.  (<literal>foreigntableid</> could be obtained from the
+     planner data structures, but it's passed explicitly to save effort.)
     </para>
 
     <para>
-     The function must generate at least one access path (ForeignPath node)
-     for a scan on the foreign table and must call <function>add_path</> to
-     add the path to <literal>baserel-&gt;pathlist</>.  It's recommended to
-     use <function>create_foreignscan_path</> to build the ForeignPath node.
-     The function may generate multiple access paths, e.g., a path which has
-     valid <literal>pathkeys</> to represent a pre-sorted result.  Each access
-     path must contain cost estimates, and can contain any FDW-private
-     information that is needed to execute the foreign scan at a later time.
-     (Note that the private information must be represented in a form that
-     <function>copyObject</> knows how to copy.)
+     This function should update <literal>baserel-&gt;rows</> to be the
+     expected number of rows returned by the table scan, after accounting for
+     the filtering done by the restriction quals.  The initial value of
+     <literal>baserel-&gt;rows</> is just a constant default estimate, which
+     should be replaced if at all possible.  The function may also choose to
+     update <literal>baserel-&gt;width</> if it can compute a better estimate
+     of the average result row width.
     </para>
 
     <para>
-     The information in <literal>root</> and <literal>baserel</> can be used
-     to reduce the amount of information that has to be fetched from the
-     foreign table (and therefore reduce the cost estimate).
-     <literal>baserel-&gt;baserestrictinfo</> is particularly interesting, as
-     it contains restriction quals (<literal>WHERE</> clauses) that can be
-     used to filter the rows to be fetched.  (The FDW is not required to
-     enforce these quals, as the finished plan will recheck them anyway.)
-     <literal>baserel-&gt;reltargetlist</> can be used to determine which
-     columns need to be fetched.
+     See <xref linkend="fdw-planning"> for additional information.
+    </para>
+
+    <para>
+<programlisting>
+void
+GetForeignPaths (PlannerInfo *root,
+                 RelOptInfo *baserel,
+                 Oid foreigntableid);
+</programlisting>
+
+     Create possible access paths for a scan on a foreign table.
+     This is called during query planning.
+     The parameters are the same as for <function>GetForeignRelSize</>,
+     which has already been called.
+    </para>
+
+    <para>
+     This function must generate at least one access path
+     (<structname>ForeignPath</> node) for a scan on the foreign table and
+     must call <function>add_path</> to add each such path to
+     <literal>baserel-&gt;pathlist</>.  It's recommended to use
+     <function>create_foreignscan_path</> to build the
+     <structname>ForeignPath</> nodes.  The function can generate multiple
+     access paths, e.g., a path which has valid <literal>pathkeys</> to
+     represent a pre-sorted result.  Each access path must contain cost
+     estimates, and can contain any FDW-private information that is needed to
+     identify the specific scan method intended.
+    </para>
+
+    <para>
+     See <xref linkend="fdw-planning"> for additional information.
+    </para>
+
+    <para>
+<programlisting>
+ForeignScan *
+GetForeignPlan (PlannerInfo *root,
+                RelOptInfo *baserel,
+                Oid foreigntableid,
+                ForeignPath *best_path,
+                List *tlist,
+                List *scan_clauses);
+</programlisting>
+
+     Create a <structname>ForeignScan</> plan node from the selected foreign
+     access path.  This is called at the end of query planning.
+     The parameters are as for <function>GetForeignRelSize</>, plus
+     the selected <structname>ForeignPath</> (previously produced by
+     <function>GetForeignPaths</>), the target list to be emitted by the
+     plan node, and the restriction clauses to be enforced by the plan node.
     </para>
 
     <para>
-     In addition to returning cost estimates, the function should update
-     <literal>baserel-&gt;rows</> to be the expected number of rows returned
-     by the scan, after accounting for the filtering done by the restriction
-     quals.  The initial value of <literal>baserel-&gt;rows</> is just a
-     constant default estimate, which should be replaced if at all possible.
-     The function may also choose to update <literal>baserel-&gt;width</> if
-     it can compute a better estimate of the average result row width.
+     This function must create and return a <structname>ForeignScan</> plan
+     node; it's recommended to use <function>make_foreignscan</> to build the
+     <structname>ForeignScan</> node.
+    </para>
+
+    <para>
+     See <xref linkend="fdw-planning"> for additional information.
     </para>
 
     <para>
@@ -170,7 +210,7 @@ BeginForeignScan (ForeignScanState *node,
      the table to scan is accessible through the
      <structname>ForeignScanState</> node (in particular, from the underlying
      <structname>ForeignScan</> plan node, which contains any FDW-private
-     information provided by <function>PlanForeignScan</>).
+     information provided by <function>GetForeignPlan</>).
     </para>
 
     <para>
@@ -347,6 +387,126 @@ GetForeignServerByName(const char *name, bool missing_ok);
      return NULL if missing_ok is true, otherwise raise an error.
     </para>
 
+   </sect1>
+
+   <sect1 id="fdw-planning">
+    <title>Foreign Data Wrapper Query Planning</title>
+
+    <para>
+     The FDW callback functions <function>GetForeignRelSize</>,
+     <function>GetForeignPaths</>, and <function>GetForeignPlan</> must fit
+     into the workings of the <productname>PostgreSQL</> planner.  Here are
+     some notes about what they must do.
+    </para>
+
+    <para>
+     The information in <literal>root</> and <literal>baserel</> can be used
+     to reduce the amount of information that has to be fetched from the
+     foreign table (and therefore reduce the cost).
+     <literal>baserel-&gt;baserestrictinfo</> is particularly interesting, as
+     it contains restriction quals (<literal>WHERE</> clauses) that should be
+     used to filter the rows to be fetched.  (The FDW itself is not required
+     to enforce these quals, as the core executor can check them instead.)
+     <literal>baserel-&gt;reltargetlist</> can be used to determine which
+     columns need to be fetched; but note that it only lists columns that
+     have to be emitted by the <structname>ForeignScan</> plan node, not
+     columns that are used in qual evaluation but not output by the query.
+    </para>
+
+    <para>
+     Various private fields are available for the FDW planning functions to
+     keep information in.  Generally, whatever you store in FDW private fields
+     should be palloc'd, so that it will be reclaimed at the end of planning.
+    </para>
+
+    <para>
+     <literal>baserel-&gt;fdw_private</> is a <type>void</> pointer that is
+     available for FDW planning functions to store information relevant to
+     the particular foreign table.  The core planner does not touch it except
+     to initialize it to NULL when the <literal>baserel</> node is created.
+     It is useful for passing information forward from
+     <function>GetForeignRelSize</> to <function>GetForeignPaths</> and/or
+     <function>GetForeignPaths</> to <function>GetForeignPlan</>, thereby
+     avoiding recalculation.
+    </para>
+
+    <para>
+     <function>GetForeignPaths</> can identify the meaning of different
+     access paths by storing private information in the
+     <structfield>fdw_private</> field of <structname>ForeignPath</> nodes.
+     <structfield>fdw_private</> is declared as a <type>List</> pointer, but
+     could actually contain anything since the core planner does not touch
+     it.  However, best practice is to use a representation that's dumpable
+     by <function>nodeToString</>, for use with debugging support available
+     in the backend.
+    </para>
+
+    <para>
+     <function>GetForeignPlan</> can examine the <structfield>fdw_private</>
+     field of the selected <structname>ForeignPath</> node, and can generate
+     <structfield>fdw_exprs</> and <structfield>fdw_private</> lists to be
+     placed in the <structname>ForeignScan</> plan node, where they will be
+     available at execution time.  Both of these lists must be
+     represented in a form that <function>copyObject</> knows how to copy.
+     The <structfield>fdw_private</> list has no other restrictions and is
+     not interpreted by the core backend in any way.  The
+     <structfield>fdw_exprs</> list, if not NIL, is expected to contain
+     expression trees that are intended to be executed at runtime.  These
+     trees will undergo post-processing by the planner to make them fully
+     executable.
+    </para>
+
+    <para>
+     In <function>GetForeignPlan</>, generally the passed-in targetlist can
+     be copied into the plan node as-is.  The passed scan_clauses list
+     contains the same clauses as <literal>baserel-&gt;baserestrictinfo</>,
+     but may be re-ordered for better execution efficiency.  In simple cases
+     the FDW can just strip <structname>RestrictInfo</> nodes from the
+     scan_clauses list (using <function>extract_actual_clauses</>) and put
+     all the clauses into the plan node's qual list, which means that all the
+     clauses will be checked by the executor at runtime.  More complex FDWs
+     may be able to check some of the clauses internally, in which case those
+     clauses can be removed from the plan node's qual list so that the
+     executor doesn't waste time rechecking them.
+    </para>
+
+    <para>
+     As an example, the FDW might identify some restriction clauses of the
+     form <replaceable>foreign_variable</> <literal>=</>
+     <replaceable>sub_expression</>, which it determines can be executed on
+     the remote server given the locally-evaluated value of the
+     <replaceable>sub_expression</>.  The actual identification of such a
+     clause should happen during <function>GetForeignPaths</>, since it would
+     affect the cost estimate for the path.  The path's
+     <structfield>fdw_private</> field would probably include a pointer to
+     the identified clause's <structname>RestrictInfo</> node.  Then
+     <function>GetForeignPlan</> would remove that clause from scan_clauses,
+     but add the <replaceable>sub_expression</> to <structfield>fdw_exprs</>
+     to ensure that it gets massaged into executable form.  It would probably
+     also put control information into the plan node's
+     <structfield>fdw_private</> field to tell the execution functions what
+     to do at runtime.  The query transmitted to the remote server would
+     involve something like <literal>WHERE <replaceable>foreign_variable</> =
+     $1</literal>, with the parameter value obtained at runtime from
+     evaluation of the <structfield>fdw_exprs</> expression tree.
+    </para>
+
+    <para>
+     The FDW should always construct at least one path that depends only on
+     the table's restriction clauses.  In join queries, it might also choose
+     to construct path(s) that depend on join clauses, for example
+     <replaceable>foreign_variable</> <literal>=</>
+     <replaceable>local_variable</>.  Such clauses will not be found in
+     <literal>baserel-&gt;baserestrictinfo</> but must be sought in the
+     relation's join lists.  A path using such a clause is called a
+     <quote>parameterized path</>.  It must show the other relation(s) as
+     <literal>required_outer</> and list the specific join clause(s) in
+     <literal>param_clauses</>.  In <function>GetForeignPlan</>, the
+     <replaceable>local_variable</> portion of the join clause would be added
+     to <structfield>fdw_exprs</>, and then at runtime the case works the
+     same as for an ordinary restriction clause.
+    </para>
+
   </sect1>
 
  </chapter>

src/backend/nodes/copyfuncs.c

@@ -591,8 +591,9 @@ _copyForeignScan(const ForeignScan *from)
 	/*
 	 * copy remainder of node
 	 */
-	COPY_SCALAR_FIELD(fsSystemCol);
+	COPY_NODE_FIELD(fdw_exprs);
 	COPY_NODE_FIELD(fdw_private);
+	COPY_SCALAR_FIELD(fsSystemCol);
 
 	return newnode;
 }

src/backend/nodes/outfuncs.c

@@ -559,8 +559,9 @@ _outForeignScan(StringInfo str, const ForeignScan *node)
 
 	_outScanInfo(str, (const Scan *) node);
 
-	WRITE_BOOL_FIELD(fsSystemCol);
+	WRITE_NODE_FIELD(fdw_exprs);
 	WRITE_NODE_FIELD(fdw_private);
+	WRITE_BOOL_FIELD(fsSystemCol);
 }
 
 static void
@@ -1741,6 +1742,7 @@ _outRelOptInfo(StringInfo str, const RelOptInfo *node)
 	WRITE_FLOAT_FIELD(allvisfrac, "%.6f");
 	WRITE_NODE_FIELD(subplan);
 	WRITE_NODE_FIELD(subroot);
+	/* we don't try to print fdwroutine or fdw_private */
 	WRITE_NODE_FIELD(baserestrictinfo);
 	WRITE_NODE_FIELD(joininfo);
 	WRITE_BOOL_FIELD(has_eclass_joins);

src/backend/optimizer/path/allpaths.c

@@ -396,6 +396,12 @@ set_foreign_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 {
 	/* Mark rel with estimated output rows, width, etc */
 	set_foreign_size_estimates(root, rel);
+
+	/* Get FDW routine pointers for the rel */
+	rel->fdwroutine = GetFdwRoutineByRelId(rte->relid);
+
+	/* Let FDW adjust the size estimates, if it can */
+	rel->fdwroutine->GetForeignRelSize(root, rel, rte->relid);
 }
 
 /*
@@ -405,11 +411,8 @@ set_foreign_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 static void
 set_foreign_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 {
-	FdwRoutine *fdwroutine;
-
-	/* Call the FDW's PlanForeignScan function to generate path(s) */
-	fdwroutine = GetFdwRoutineByRelId(rte->relid);
-	fdwroutine->PlanForeignScan(rte->relid, root, rel);
+	/* Call the FDW's GetForeignPaths function to generate path(s) */
+	rel->fdwroutine->GetForeignPaths(root, rel, rte->relid);
 
 	/* Select cheapest path */
 	set_cheapest(rel);

src/backend/optimizer/path/costsize.c

@@ -3745,7 +3745,7 @@ set_cte_size_estimates(PlannerInfo *root, RelOptInfo *rel, Plan *cteplan)
  * using what will be purely datatype-driven estimates from the targetlist.
  * There is no way to do anything sane with the rows value, so we just put
  * a default estimate and hope that the wrapper can improve on it.	The
- * wrapper's PlanForeignScan function will be called momentarily.
+ * wrapper's GetForeignRelSize function will be called momentarily.
  *
  * The rel's targetlist and restrictinfo list must have been constructed
  * already.

src/backend/optimizer/plan/createplan.c

@@ -20,6 +20,7 @@
 #include <math.h>
 
 #include "access/skey.h"
+#include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
@@ -119,8 +120,6 @@ static CteScan *make_ctescan(List *qptlist, List *qpqual,
 			 Index scanrelid, int ctePlanId, int cteParam);
 static WorkTableScan *make_worktablescan(List *qptlist, List *qpqual,
 				   Index scanrelid, int wtParam);
-static ForeignScan *make_foreignscan(List *qptlist, List *qpqual,
-				 Index scanrelid, bool fsSystemCol, List *fdw_private);
 static BitmapAnd *make_bitmap_and(List *bitmapplans);
 static BitmapOr *make_bitmap_or(List *bitmapplans);
 static NestLoop *make_nestloop(List *tlist,
@@ -1816,7 +1815,6 @@ create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
 	RelOptInfo *rel = best_path->path.parent;
 	Index		scan_relid = rel->relid;
 	RangeTblEntry *rte;
-	bool		fsSystemCol;
 	int			i;
 
 	/* it should be a base rel... */
@@ -1825,31 +1823,56 @@ create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
 	rte = planner_rt_fetch(scan_relid, root);
 	Assert(rte->rtekind == RTE_RELATION);
 
-	/* Sort clauses into best execution order */
+	/*
+	 * Sort clauses into best execution order.  We do this first since the
+	 * FDW might have more info than we do and wish to adjust the ordering.
+	 */
 	scan_clauses = order_qual_clauses(root, scan_clauses);
 
-	/* Reduce RestrictInfo list to bare expressions; ignore pseudoconstants */
-	scan_clauses = extract_actual_clauses(scan_clauses, false);
+	/*
+	 * Let the FDW perform its processing on the restriction clauses and
+	 * generate the plan node.  Note that the FDW might remove restriction
+	 * clauses that it intends to execute remotely, or even add more (if it
+	 * has selected some join clauses for remote use but also wants them
+	 * rechecked locally).
+	 */
+	scan_plan = rel->fdwroutine->GetForeignPlan(root, rel, rte->relid,
+												best_path,
+												tlist, scan_clauses);
+
+	/* Copy cost data from Path to Plan; no need to make FDW do this */
+	copy_path_costsize(&scan_plan->scan.plan, &best_path->path);
 
-	/* Detect whether any system columns are requested from rel */
-	fsSystemCol = false;
+	/*
+	 * Replace any outer-relation variables with nestloop params in the qual
+	 * and fdw_exprs expressions.  We do this last so that the FDW doesn't
+	 * have to be involved.  (Note that parts of fdw_exprs could have come
+	 * from join clauses, so doing this beforehand on the scan_clauses
+	 * wouldn't work.)
+	 */
+	if (best_path->path.required_outer)
+	{
+		scan_plan->scan.plan.qual = (List *)
+			replace_nestloop_params(root, (Node *) scan_plan->scan.plan.qual);
+		scan_plan->fdw_exprs = (List *)
+			replace_nestloop_params(root, (Node *) scan_plan->fdw_exprs);
+	}
+
+	/*
+	 * Detect whether any system columns are requested from rel.  This is a
+	 * bit of a kluge and might go away someday, so we intentionally leave it
+	 * out of the API presented to FDWs.
+	 */
+	scan_plan->fsSystemCol = false;
 	for (i = rel->min_attr; i < 0; i++)
 	{
 		if (!bms_is_empty(rel->attr_needed[i - rel->min_attr]))
 		{
-			fsSystemCol = true;
+			scan_plan->fsSystemCol = true;
 			break;
 		}
 	}
 
-	scan_plan = make_foreignscan(tlist,
-								 scan_clauses,
-								 scan_relid,
-								 fsSystemCol,
-								 best_path->fdw_private);
-
-	copy_path_costsize(&scan_plan->scan.plan, &best_path->path);
-
 	return scan_plan;
 }
 
@@ -3183,24 +3206,26 @@ make_worktablescan(List *qptlist,
 	return node;
 }
 
-static ForeignScan *
+ForeignScan *
 make_foreignscan(List *qptlist,
 				 List *qpqual,
 				 Index scanrelid,
-				 bool fsSystemCol,
+				 List *fdw_exprs,
 				 List *fdw_private)
 {
 	ForeignScan *node = makeNode(ForeignScan);
 	Plan	   *plan = &node->scan.plan;
 
-	/* cost should be inserted by caller */
+	/* cost will be filled in by create_foreignscan_plan */
 	plan->targetlist = qptlist;
 	plan->qual = qpqual;
 	plan->lefttree = NULL;
 	plan->righttree = NULL;
 	node->scan.scanrelid = scanrelid;
-	node->fsSystemCol = fsSystemCol;
+	node->fdw_exprs = fdw_exprs;
 	node->fdw_private = fdw_private;
+	/* fsSystemCol will be filled in by create_foreignscan_plan */
+	node->fsSystemCol = false;
 
 	return node;
 }

src/backend/optimizer/plan/setrefs.c

@@ -428,6 +428,8 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 					fix_scan_list(root, splan->scan.plan.targetlist, rtoffset);
 				splan->scan.plan.qual =
 					fix_scan_list(root, splan->scan.plan.qual, rtoffset);
+				splan->fdw_exprs =
+					fix_scan_list(root, splan->fdw_exprs, rtoffset);
 			}
 			break;
 

src/backend/optimizer/plan/subselect.c

@@ -2137,6 +2137,8 @@ finalize_plan(PlannerInfo *root, Plan *plan, Bitmapset *valid_params,
 			break;
 
 		case T_ForeignScan:
+			finalize_primnode((Node *) ((ForeignScan *) plan)->fdw_exprs,
+							  &context);
 			context.paramids = bms_add_members(context.paramids, scan_params);
 			break;
 

src/backend/optimizer/util/pathnode.c

@@ -1767,7 +1767,7 @@ create_worktablescan_path(PlannerInfo *root, RelOptInfo *rel)
  *	  returning the pathnode.
  *
  * This function is never called from core Postgres; rather, it's expected
- * to be called by the PlanForeignScan function of a foreign data wrapper.
+ * to be called by the GetForeignPaths function of a foreign data wrapper.
  * We make the FDW supply all fields of the path, since we do not have any
  * way to calculate them in core.
  */

src/backend/optimizer/util/relnode.c

@@ -113,6 +113,8 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->allvisfrac = 0;
 	rel->subplan = NULL;
 	rel->subroot = NULL;
+	rel->fdwroutine = NULL;
+	rel->fdw_private = NULL;
 	rel->baserestrictinfo = NIL;
 	rel->baserestrictcost.startup = 0;
 	rel->baserestrictcost.per_tuple = 0;
@@ -366,6 +368,8 @@ build_join_rel(PlannerInfo *root,
 	joinrel->allvisfrac = 0;
 	joinrel->subplan = NULL;
 	joinrel->subroot = NULL;
+	joinrel->fdwroutine = NULL;
+	joinrel->fdw_private = NULL;
 	joinrel->baserestrictinfo = NIL;
 	joinrel->baserestrictcost.startup = 0;
 	joinrel->baserestrictcost.per_tuple = 0;

src/include/foreign/fdwapi.h

@@ -23,9 +23,20 @@ struct ExplainState;
  * Callback function signatures --- see fdwhandler.sgml for more info.
  */
 
-typedef void (*PlanForeignScan_function) (Oid foreigntableid,
-										  PlannerInfo *root,
-										  RelOptInfo *baserel);
+typedef void (*GetForeignRelSize_function) (PlannerInfo *root,
+											RelOptInfo *baserel,
+											Oid foreigntableid);
+
+typedef void (*GetForeignPaths_function) (PlannerInfo *root,
+										  RelOptInfo *baserel,
+										  Oid foreigntableid);
+
+typedef ForeignScan *(*GetForeignPlan_function) (PlannerInfo *root,
+												 RelOptInfo *baserel,
+												 Oid foreigntableid,
+												 ForeignPath *best_path,
+												 List *tlist,
+												 List *scan_clauses);
 
 typedef void (*ExplainForeignScan_function) (ForeignScanState *node,
 													struct ExplainState *es);
@@ -53,7 +64,9 @@ typedef struct FdwRoutine
 {
 	NodeTag		type;
 
-	PlanForeignScan_function PlanForeignScan;
+	GetForeignRelSize_function GetForeignRelSize;
+	GetForeignPaths_function GetForeignPaths;
+	GetForeignPlan_function GetForeignPlan;
 	ExplainForeignScan_function ExplainForeignScan;
 	BeginForeignScan_function BeginForeignScan;
 	IterateForeignScan_function IterateForeignScan;

src/include/nodes/plannodes.h

@@ -462,13 +462,22 @@ typedef struct WorkTableScan
 
 /* ----------------
  *		ForeignScan node
+ *
+ * fdw_exprs and fdw_private are both under the control of the foreign-data
+ * wrapper, but fdw_exprs is presumed to contain expression trees and will
+ * be post-processed accordingly by the planner; fdw_private won't be.
+ * Note that everything in both lists must be copiable by copyObject().
+ * One way to store an arbitrary blob of bytes is to represent it as a bytea
+ * Const.  Usually, though, you'll be better off choosing a representation
+ * that can be dumped usefully by nodeToString().
  * ----------------
  */
 typedef struct ForeignScan
 {
 	Scan		scan;
-	bool		fsSystemCol;	/* true if any "system column" is needed */
+	List	   *fdw_exprs;		/* expressions that FDW may evaluate */
 	List	   *fdw_private;	/* private data for FDW */
+	bool		fsSystemCol;	/* true if any "system column" is needed */
 } ForeignScan;
 
 

src/include/nodes/relation.h

@@ -334,10 +334,13 @@ typedef struct PlannerInfo
  *		allvisfrac - fraction of disk pages that are marked all-visible
  *		subplan - plan for subquery (NULL if it's not a subquery)
  *		subroot - PlannerInfo for subquery (NULL if it's not a subquery)
+ *		fdwroutine - function hooks for FDW, if foreign table (else NULL)
+ *		fdw_private - private state for FDW, if foreign table (else NULL)
  *
  *		Note: for a subquery, tuples, subplan, subroot are not set immediately
  *		upon creation of the RelOptInfo object; they are filled in when
- *		set_base_rel_pathlist processes the object.
+ *		set_subquery_pathlist processes the object.  Likewise, fdwroutine
+ *		and fdw_private are filled during initial path creation.
  *
  *		For otherrels that are appendrel members, these fields are filled
  *		in just as for a baserel.
@@ -414,8 +417,12 @@ typedef struct RelOptInfo
 	BlockNumber pages;			/* size estimates derived from pg_class */
 	double		tuples;
 	double		allvisfrac;
+	/* use "struct Plan" to avoid including plannodes.h here */
 	struct Plan *subplan;		/* if subquery */
 	PlannerInfo *subroot;		/* if subquery */
+	/* use "struct FdwRoutine" to avoid including fdwapi.h here */
+	struct FdwRoutine *fdwroutine;	/* if foreign table */
+	void	   *fdw_private;	/* if foreign table */
 
 	/* used by various scans and joins: */
 	List	   *baserestrictinfo;		/* RestrictInfo structures (if base
@@ -793,14 +800,13 @@ typedef struct TidPath
 } TidPath;
 
 /*
- * ForeignPath represents a scan of a foreign table
- *
- * fdw_private contains FDW private data about the scan, which will be copied
- * to the final ForeignScan plan node so that it is available at execution
- * time.  Note that everything in this list must be copiable by copyObject().
- * One way to store an arbitrary blob of bytes is to represent it as a bytea
- * Const.  Usually, though, you'll be better off choosing a representation
- * that can be dumped usefully by nodeToString().
+ * ForeignPath represents a potential scan of a foreign table
+ *
+ * fdw_private stores FDW private data about the scan.  While fdw_private is
+ * not actually touched by the core code during normal operations, it's
+ * generally a good idea to use a representation that can be dumped by
+ * nodeToString(), so that you can examine the structure during debugging
+ * with tools like pprint().
  */
 typedef struct ForeignPath
 {

src/include/optimizer/planmain.h

@@ -42,6 +42,8 @@ extern Plan *optimize_minmax_aggregates(PlannerInfo *root, List *tlist,
 extern Plan *create_plan(PlannerInfo *root, Path *best_path);
 extern SubqueryScan *make_subqueryscan(List *qptlist, List *qpqual,
 				  Index scanrelid, Plan *subplan);
+extern ForeignScan *make_foreignscan(List *qptlist, List *qpqual,
+				 Index scanrelid, List *fdw_exprs, List *fdw_private);
 extern Append *make_append(List *appendplans, List *tlist);
 extern RecursiveUnion *make_recursive_union(List *tlist,
 					 Plan *lefttree, Plan *righttree, int wtParam,