2 files changed, 116 insertions, 0 deletions

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 9caca94f64b..4cd1bf65e74 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -71,6 +71,10 @@ static void set_plain_rel_size(PlannerInfo *root, RelOptInfo *rel,
 				   RangeTblEntry *rte);
 static void set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 					   RangeTblEntry *rte);
+static void set_tablesample_rel_size(PlannerInfo *root, RelOptInfo *rel,
+				   RangeTblEntry *rte);
+static void set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
+										 RangeTblEntry *rte);
 static void set_foreign_size(PlannerInfo *root, RelOptInfo *rel,
 				 RangeTblEntry *rte);
 static void set_foreign_pathlist(PlannerInfo *root, RelOptInfo *rel,
@@ -265,6 +269,11 @@ set_rel_size(PlannerInfo *root, RelOptInfo *rel,
 					/* Foreign table */
 					set_foreign_size(root, rel, rte);
 				}
+				else if (rte->tablesample != NULL)
+				{
+					/* Sampled relation */
+					set_tablesample_rel_size(root, rel, rte);
+				}
 				else
 				{
 					/* Plain relation */
@@ -332,6 +341,11 @@ set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 					/* Foreign table */
 					set_foreign_pathlist(root, rel, rte);
 				}
+				else if (rte->tablesample != NULL)
+				{
+					/* Build sample scan on relation */
+					set_tablesample_rel_pathlist(root, rel, rte);
+				}
 				else
 				{
 					/* Plain relation */
@@ -418,6 +432,41 @@ set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 }
 
 /*
+ * set_tablesample_rel_size
+ *	  Set size estimates for a sampled relation.
+ */
+static void
+set_tablesample_rel_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	/* Mark rel with estimated output rows, width, etc */
+	set_baserel_size_estimates(root, rel);
+}
+
+/*
+ * set_tablesample_rel_pathlist
+ *	  Build access paths for a sampled relation
+ *
+ * There is only one possible path - sampling scan
+ */
+static void
+set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
+{
+	Relids	required_outer;
+	Path   *path;
+
+	/*
+	 * We don't support pushing join clauses into the quals of a seqscan, but
+	 * it could still have required parameterization due to LATERAL refs in
+	 * its tlist.
+	 */
+	required_outer = rel->lateral_relids;
+
+	/* We only do sample scan if it was requested */
+	path = create_samplescan_path(root, rel, required_outer);
+	rel->pathlist = list_make1(path);
+}
+
+/*
  * set_foreign_size
  *		Set size estimates for a foreign table RTE
  */
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 1a0d358c5f7..c2b2b7622a6 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -220,6 +220,73 @@ cost_seqscan(Path *path, PlannerInfo *root,
 }
 
 /*
+ * cost_samplescan
+ *	  Determines and returns the cost of scanning a relation using sampling.
+ *
+ * From planner/optimizer perspective, we don't care all that much about cost
+ * itself since there is always only one scan path to consider when sampling
+ * scan is present, but number of rows estimation is still important.
+ *
+ * 'baserel' is the relation to be scanned
+ * 'param_info' is the ParamPathInfo if this is a parameterized path, else NULL
+ */
+void
+cost_samplescan(Path *path, PlannerInfo *root, RelOptInfo *baserel)
+{
+	Cost		startup_cost = 0;
+	Cost		run_cost = 0;
+	double		spc_seq_page_cost,
+				spc_random_page_cost,
+				spc_page_cost;
+	QualCost	qpqual_cost;
+	Cost		cpu_per_tuple;
+	BlockNumber pages;
+	double		tuples;
+	RangeTblEntry		   *rte = planner_rt_fetch(baserel->relid, root);
+	TableSampleClause	   *tablesample = rte->tablesample;
+
+	/* Should only be applied to base relations */
+	Assert(baserel->relid > 0);
+	Assert(baserel->rtekind == RTE_RELATION);
+
+	/* Mark the path with the correct row estimate */
+	if (path->param_info)
+		path->rows = path->param_info->ppi_rows;
+	else
+		path->rows = baserel->rows;
+
+	/* Call the sampling method's costing function. */
+	OidFunctionCall6(tablesample->tsmcost, PointerGetDatum(root),
+					 PointerGetDatum(path), PointerGetDatum(baserel),
+					 PointerGetDatum(tablesample->args),
+					 PointerGetDatum(&pages), PointerGetDatum(&tuples));
+
+	/* fetch estimated page cost for tablespace containing table */
+	get_tablespace_page_costs(baserel->reltablespace,
+							  &spc_random_page_cost,
+							  &spc_seq_page_cost);
+
+
+	spc_page_cost = tablesample->tsmseqscan ? spc_seq_page_cost :
+					spc_random_page_cost;
+
+	/*
+	 * disk costs
+	 */
+	run_cost += spc_page_cost * pages;
+
+	/* CPU costs */
+	get_restriction_qual_cost(root, baserel, path->param_info, &qpqual_cost);
+
+	startup_cost += qpqual_cost.startup;
+	cpu_per_tuple = cpu_tuple_cost + qpqual_cost.per_tuple;
+	run_cost += cpu_per_tuple * tuples;
+
+	path->startup_cost = startup_cost;
+	path->total_cost = startup_cost + run_cost;
+}
+
+/*
  * cost_index
  *	  Determines and returns the cost of scanning a relation using an index.
  *