4 files changed, 124 insertions, 9 deletions

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 903e80aea35..298eebf5e67 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -32,6 +32,7 @@
 #include "catalog/pg_opclass.h"
 #include "catalog/pg_operator.h"
 #include "catalog/pg_proc.h"
+#include "catalog/pg_tablesample_method.h"
 #include "catalog/pg_trigger.h"
 #include "catalog/pg_type.h"
 #include "commands/defrem.h"
@@ -345,6 +346,8 @@ static void make_ruledef(StringInfo buf, HeapTuple ruletup, TupleDesc rulettc,
 			 int prettyFlags);
 static void make_viewdef(StringInfo buf, HeapTuple ruletup, TupleDesc rulettc,
 			 int prettyFlags, int wrapColumn);
+static void get_tablesample_def(TableSampleClause *tablesample,
+								deparse_context *context);
 static void get_query_def(Query *query, StringInfo buf, List *parentnamespace,
 			  TupleDesc resultDesc,
 			  int prettyFlags, int wrapColumn, int startIndent);
@@ -4220,6 +4223,50 @@ make_viewdef(StringInfo buf, HeapTuple ruletup, TupleDesc rulettc,
 	heap_close(ev_relation, AccessShareLock);
 }
 
+/* ----------
+ * get_tablesample_def			- Convert TableSampleClause back to SQL
+ * ----------
+ */
+static void
+get_tablesample_def(TableSampleClause *tablesample, deparse_context *context)
+{
+	StringInfo	buf = context->buf;
+	HeapTuple	tuple;
+	Form_pg_tablesample_method tsm;
+	char	   *tsmname;
+	int			nargs;
+	ListCell   *l;
+
+	/* Load the tablesample method */
+	tuple = SearchSysCache1(TABLESAMPLEMETHODOID, ObjectIdGetDatum(tablesample->tsmid));
+	if (!HeapTupleIsValid(tuple))
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("cache lookup failed for tablesample method %u",
+						tablesample->tsmid)));
+
+	tsm = (Form_pg_tablesample_method) GETSTRUCT(tuple);
+	tsmname = NameStr(tsm->tsmname);
+	appendStringInfo(buf, " TABLESAMPLE %s (", quote_identifier(tsmname));
+
+	ReleaseSysCache(tuple);
+
+	nargs = 0;
+	foreach(l, tablesample->args)
+	{
+		if (nargs++ > 0)
+			appendStringInfoString(buf, ", ");
+		get_rule_expr((Node *) lfirst(l), context, true);
+	}
+	appendStringInfoChar(buf, ')');
+
+	if (tablesample->repeatable != NULL)
+	{
+		appendStringInfoString(buf, " REPEATABLE (");
+		get_rule_expr(tablesample->repeatable, context, true);
+		appendStringInfoChar(buf, ')');
+	}
+}
 
 /* ----------
  * get_query_def			- Parse back one query parsetree
@@ -8529,6 +8576,9 @@ get_from_clause_item(Node *jtnode, Query *query, deparse_context *context)
 								 only_marker(rte),
 								 generate_relation_name(rte->relid,
 														context->namespaces));
+
+				if (rte->tablesample)
+					get_tablesample_def(rte->tablesample, context);
 				break;
 			case RTE_SUBQUERY:
 				/* Subquery RTE */
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 1dc293297d9..f259751e157 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -32,6 +32,7 @@
 #include "catalog/pg_range.h"
 #include "catalog/pg_statistic.h"
 #include "catalog/pg_transform.h"
+#include "catalog/pg_tablesample_method.h"
 #include "catalog/pg_type.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -2996,3 +2997,29 @@ get_range_subtype(Oid rangeOid)
 	else
 		return InvalidOid;
 }
+
+/*				---------- PG_TABLESAMPLE_METHOD CACHE ----------			 */
+
+/*
+ * get_tablesample_method_name - given a tablesample method OID,
+ * look up the name or NULL if not found
+ */
+char *
+get_tablesample_method_name(Oid tsmid)
+{
+	HeapTuple	tuple;
+
+	tuple = SearchSysCache1(TABLESAMPLEMETHODOID, ObjectIdGetDatum(tsmid));
+	if (HeapTupleIsValid(tuple))
+	{
+		Form_pg_tablesample_method	tup =
+			(Form_pg_tablesample_method) GETSTRUCT(tuple);
+		char	   *result;
+
+		result = pstrdup(NameStr(tup->tsmname));
+		ReleaseSysCache(tuple);
+		return result;
+	}
+	else
+		return NULL;
+}
diff --git a/src/backend/utils/cache/syscache.c b/src/backend/utils/cache/syscache.c
index f58e1cebf2a..7def1be32ae 100644
--- a/src/backend/utils/cache/syscache.c
+++ b/src/backend/utils/cache/syscache.c
@@ -56,6 +56,7 @@
 #include "catalog/pg_shseclabel.h"
 #include "catalog/pg_replication_origin.h"
 #include "catalog/pg_statistic.h"
+#include "catalog/pg_tablesample_method.h"
 #include "catalog/pg_tablespace.h"
 #include "catalog/pg_transform.h"
 #include "catalog/pg_ts_config.h"
@@ -666,6 +667,28 @@ static const struct cachedesc cacheinfo[] = {
 		},
 		128
 	},
+	{TableSampleMethodRelationId,		/* TABLESAMPLEMETHODNAME */
+		TableSampleMethodNameIndexId,
+		1,
+		{
+			Anum_pg_tablesample_method_tsmname,
+			0,
+			0,
+			0,
+		},
+		2
+	},
+	{TableSampleMethodRelationId,		/* TABLESAMPLEMETHODOID */
+		TableSampleMethodOidIndexId,
+		1,
+		{
+			ObjectIdAttributeNumber,
+			0,
+			0,
+			0,
+		},
+		2
+	},
 	{TableSpaceRelationId,		/* TABLESPACEOID */
 		TablespaceOidIndexId,
 		1,
diff --git a/src/backend/utils/misc/sampling.c b/src/backend/utils/misc/sampling.c
index 1eeabaf1588..9becc63bf82 100644
--- a/src/backend/utils/misc/sampling.c
+++ b/src/backend/utils/misc/sampling.c
@@ -46,6 +46,8 @@ BlockSampler_Init(BlockSampler bs, BlockNumber nblocks, int samplesize,
 	bs->n = samplesize;
 	bs->t = 0;					/* blocks scanned so far */
 	bs->m = 0;					/* blocks selected so far */
+
+	sampler_random_init_state(randseed, bs->randstate);
 }
 
 bool
@@ -92,7 +94,7 @@ BlockSampler_Next(BlockSampler bs)
 	 * less than k, which means that we cannot fail to select enough blocks.
 	 *----------
 	 */
-	V = sampler_random_fract();
+	V = sampler_random_fract(bs->randstate);
 	p = 1.0 - (double) k / (double) K;
 	while (V < p)
 	{
@@ -126,8 +128,14 @@ BlockSampler_Next(BlockSampler bs)
 void
 reservoir_init_selection_state(ReservoirState rs, int n)
 {
+	/*
+	 * Reservoir sampling is not used anywhere where it would need to return
+	 * repeatable results so we can initialize it randomly.
+	 */
+	sampler_random_init_state(random(), rs->randstate);
+
 	/* Initial value of W (for use when Algorithm Z is first applied) */
-	*rs = exp(-log(sampler_random_fract()) / n);
+	rs->W = exp(-log(sampler_random_fract(rs->randstate)) / n);
 }
 
 double
@@ -142,7 +150,7 @@ reservoir_get_next_S(ReservoirState rs, double t, int n)
 		double		V,
 					quot;
 
-		V = sampler_random_fract(); /* Generate V */
+		V = sampler_random_fract(rs->randstate); /* Generate V */
 		S = 0;
 		t += 1;
 		/* Note: "num" in Vitter's code is always equal to t - n */
@@ -158,7 +166,7 @@ reservoir_get_next_S(ReservoirState rs, double t, int n)
 	else
 	{
 		/* Now apply Algorithm Z */
-		double		W = *rs;
+		double		W = rs->W;
 		double		term = t - (double) n + 1;
 
 		for (;;)
@@ -174,7 +182,7 @@ reservoir_get_next_S(ReservoirState rs, double t, int n)
 						tmp;
 
 			/* Generate U and X */
-			U = sampler_random_fract();
+			U = sampler_random_fract(rs->randstate);
 			X = t * (W - 1.0);
 			S = floor(X);		/* S is tentatively set to floor(X) */
 			/* Test if U <= h(S)/cg(X) in the manner of (6.3) */
@@ -203,11 +211,11 @@ reservoir_get_next_S(ReservoirState rs, double t, int n)
 				y *= numer / denom;
 				denom -= 1;
 			}
-			W = exp(-log(sampler_random_fract()) / n);		/* Generate W in advance */
+			W = exp(-log(sampler_random_fract(rs->randstate)) / n);		/* Generate W in advance */
 			if (exp(log(y) / n) <= (t + X) / t)
 				break;
 		}
-		*rs = W;
+		rs->W = W;
 	}
 	return S;
 }
@@ -217,10 +225,17 @@ reservoir_get_next_S(ReservoirState rs, double t, int n)
  * Random number generator used by sampling
  *----------
  */
+void
+sampler_random_init_state(long seed, SamplerRandomState randstate)
+{
+	randstate[0] = RAND48_SEED_0;
+	randstate[1] = (unsigned short) seed;
+	randstate[2] = (unsigned short) (seed >> 16);
+}
 
 /* Select a random value R uniformly distributed in (0 - 1) */
 double
-sampler_random_fract()
+sampler_random_fract(SamplerRandomState randstate)
 {
-	return ((double) random() + 1) / ((double) MAX_RANDOM_VALUE + 2);
+	return pg_erand48(randstate);
 }