Add infrastructure to support EphemeralNamedRelation references.

A QueryEnvironment concept is added, which allows new types of
objects to be passed into queries from parsing on through
execution.  At this point, the only thing implemented is a
collection of EphemeralNamedRelation objects -- relations which
can be referenced by name in queries, but do not exist in the
catalogs.  The only type of ENR implemented is NamedTuplestore, but
provision is made to add more types fairly easily.

An ENR can carry its own TupleDesc or reference a relation in the
catalogs by relid.

Although these features can be used without SPI, convenience
functions are added to SPI so that ENRs can easily be used by code
run through SPI.

The initial use of all this is going to be transition tables in
AFTER triggers, but that will be added to each PL as a separate
commit.

An incidental effect of this patch is to produce a more informative
error message if an attempt is made to modify the contents of a CTE
from a referencing DML statement.  No tests previously covered that
possibility, so one is added.

Kevin Grittner and Thomas Munro
Reviewed by Heikki Linnakangas, David Fetter, and Thomas Munro
with valuable comments and suggestions from many others

src/backend/optimizer/path/allpaths.c

@@ -111,6 +111,8 @@ static void set_tablefunc_pathlist(PlannerInfo *root, RelOptInfo *rel,
 					   RangeTblEntry *rte);
 static void set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel,
 				 RangeTblEntry *rte);
+static void set_namedtuplestore_pathlist(PlannerInfo *root, RelOptInfo *rel,
+				 RangeTblEntry *rte);
 static void set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel,
 					   RangeTblEntry *rte);
 static RelOptInfo *make_rel_from_joinlist(PlannerInfo *root, List *joinlist);
@@ -396,6 +398,9 @@ set_rel_size(PlannerInfo *root, RelOptInfo *rel,
 				else
 					set_cte_pathlist(root, rel, rte);
 				break;
+			case RTE_NAMEDTUPLESTORE:
+				set_namedtuplestore_pathlist(root, rel, rte);
+				break;
 			default:
 				elog(ERROR, "unexpected rtekind: %d", (int) rel->rtekind);
 				break;
@@ -464,6 +469,9 @@ set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 			case RTE_CTE:
 				/* CTE reference --- fully handled during set_rel_size */
 				break;
+			case RTE_NAMEDTUPLESTORE:
+				/* tuplestore reference --- fully handled during set_rel_size */
+				break;
 			default:
 				elog(ERROR, "unexpected rtekind: %d", (int) rel->rtekind);
 				break;
@@ -639,6 +647,13 @@ set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
 			 * executed only once.
 			 */
 			return;
+
+		case RTE_NAMEDTUPLESTORE:
+			/*
+			 * tuplestore cannot be shared, at least without more
+			 * infrastructure to support that.
+			 */
+			return;
 	}
 
 	/*
@@ -2089,6 +2104,36 @@ set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 	add_path(rel, create_ctescan_path(root, rel, required_outer));
 }
 
+/*
+ * set_namedtuplestore_pathlist
+ *		Build the (single) access path for a named tuplestore RTE
+ *
+ * There's no need for a separate set_namedtuplestore_size phase, since we
+ * don't support join-qual-parameterized paths for tuplestores.
+ */
+static void
+set_namedtuplestore_pathlist(PlannerInfo *root, RelOptInfo *rel,
+							 RangeTblEntry *rte)
+{
+	Relids		required_outer;
+
+	/* Mark rel with estimated output rows, width, etc */
+	set_namedtuplestore_size_estimates(root, rel);
+
+	/*
+	 * We don't support pushing join clauses into the quals of a tuplestore
+	 * scan, but it could still have required parameterization due to LATERAL
+	 * refs in its tlist.
+	 */
+	required_outer = rel->lateral_relids;
+
+	/* Generate appropriate path */
+	add_path(rel, create_namedtuplestorescan_path(root, rel, required_outer));
+
+	/* Select cheapest path (pretty easy in this case...) */
+	set_cheapest(rel);
+}
+
 /*
  * set_worktable_pathlist
  *		Build the (single) access path for a self-reference CTE RTE

src/backend/optimizer/path/costsize.c

@@ -1516,6 +1516,43 @@ cost_ctescan(Path *path, PlannerInfo *root,
 	path->total_cost = startup_cost + run_cost;
 }
 
+/*
+ * cost_namedtuplestorescan
+ *	  Determines and returns the cost of scanning a named tuplestore.
+ */
+void
+cost_namedtuplestorescan(Path *path, PlannerInfo *root,
+						 RelOptInfo *baserel, ParamPathInfo *param_info)
+{
+	Cost		startup_cost = 0;
+	Cost		run_cost = 0;
+	QualCost	qpqual_cost;
+	Cost		cpu_per_tuple;
+
+	/* Should only be applied to base relations that are Tuplestores */
+	Assert(baserel->relid > 0);
+	Assert(baserel->rtekind == RTE_NAMEDTUPLESTORE);
+
+	/* Mark the path with the correct row estimate */
+	if (param_info)
+		path->rows = param_info->ppi_rows;
+	else
+		path->rows = baserel->rows;
+
+	/* Charge one CPU tuple cost per row for tuplestore manipulation */
+	cpu_per_tuple = cpu_tuple_cost;
+
+	/* Add scanning CPU costs */
+	get_restriction_qual_cost(root, baserel, param_info, &qpqual_cost);
+
+	startup_cost += qpqual_cost.startup;
+	cpu_per_tuple += cpu_tuple_cost + qpqual_cost.per_tuple;
+	run_cost += cpu_per_tuple * baserel->tuples;
+
+	path->startup_cost = startup_cost;
+	path->total_cost = startup_cost + run_cost;
+}
+
 /*
  * cost_recursive_union
  *	  Determines and returns the cost of performing a recursive union,
@@ -4684,6 +4721,39 @@ set_cte_size_estimates(PlannerInfo *root, RelOptInfo *rel, double cte_rows)
 	set_baserel_size_estimates(root, rel);
 }
 
+/*
+ * set_namedtuplestore_size_estimates
+ *		Set the size estimates for a base relation that is a tuplestore reference.
+ *
+ * The rel's targetlist and restrictinfo list must have been constructed
+ * already.
+ *
+ * We set the same fields as set_baserel_size_estimates.
+ */
+void
+set_namedtuplestore_size_estimates(PlannerInfo *root, RelOptInfo *rel)
+{
+	RangeTblEntry *rte;
+
+	/* Should only be applied to base relations that are tuplestore references */
+	Assert(rel->relid > 0);
+	rte = planner_rt_fetch(rel->relid, root);
+	Assert(rte->rtekind == RTE_NAMEDTUPLESTORE);
+
+	/*
+	 * Use the estimate provided by the code which is generating the named
+	 * tuplestore.  In some cases, the actual number might be available; in
+	 * others the same plan will be re-used, so a "typical" value might be
+	 * estimated and used.
+	 */
+	rel->tuples = rte->enrtuples;
+	if (rel->tuples < 0)
+		rel->tuples = 1000;
+
+	/* Now estimate number of output rows, etc */
+	set_baserel_size_estimates(root, rel);
+}
+
 /*
  * set_foreign_size_estimates
  *		Set the size estimates for a base relation that is a foreign table.