Fix some problems in check_new_partition_bound().

Account for the fact that the highest bound less than or equal to the
upper bound might be either the lower or the upper bound of the
overlapping partition, depending on whether the proposed partition
completely contains the existing partition or merely overlaps it.

Also, we need not continue searching for even greater bound in
partition_bound_bsearch() once we find the first bound that is *equal*
to the probe, because we don't have duplicate datums.  That spends
cycles needlessly.

Amit Langote, per a report from Amul Sul.  Cosmetic changes by me.

Discussion: http://postgr.es/m/CAAJ_b94XgbqVoXMyxxs63CaqWoMS1o2gpHiU0F7yGnJBnvDc_A%40mail.gmail.com

src/backend/catalog/partition.c

@@ -741,37 +741,68 @@ check_new_partition_bound(char *relname, Relation parent, Node *bound)
 						   boundinfo->strategy == PARTITION_STRATEGY_RANGE);
 
 					/*
-					 * Find the greatest index of a range bound that is less
+					 * Firstly, find the greatest range bound that is less
-					 * than or equal with the new lower bound.
+					 * than or equal to the new lower bound.
 					 */
 					off1 = partition_bound_bsearch(key, boundinfo, lower, true,
 												   &equal);
 
 					/*
-					 * If equal has been set to true, that means the new lower
+					 * off1 == -1 means that all existing bounds are greater
-					 * bound is found to be equal with the bound at off1,
+					 * than the new lower bound.  In that case and the case
-					 * which clearly means an overlap with the partition at
+					 * where no partition is defined between the bounds at
-					 * index off1+1).
+					 * off1 and off1 + 1, we have a "gap" in the range that
-					 *
+					 * could be occupied by the new partition.  We confirm if
-					 * Otherwise, check if there is a "gap" that could be
+					 * so by checking whether the new upper bound is confined
-					 * occupied by the new partition.  In case of a gap, the
+					 * within the gap.
-					 * new upper bound should not cross past the upper
-					 * boundary of the gap, that is, off2 == off1 should be
-					 * true.
 					 */
 					if (!equal && boundinfo->indexes[off1 + 1] < 0)
 					{
 						off2 = partition_bound_bsearch(key, boundinfo, upper,
 													   true, &equal);
 
+						/*
+						 * If the new upper bound is returned to be equal to
+						 * the bound at off2, the latter must be the upper
+						 * bound of some partition with which the new
+						 * partition clearly overlaps.
+						 *
+						 * Also, if bound at off2 is not same as the one
+						 * returned for the new lower bound (IOW, off1 !=
+						 * off2), then the new partition overlaps at least one
+						 * partition.
+						 */
 						if (equal || off1 != off2)
 						{
 							overlap = true;
-							with = boundinfo->indexes[off2 + 1];
+
+							/*
+							 * The bound at off2 could be the lower bound of
+							 * the partition with which the new partition
+							 * overlaps.  In that case, use the upper bound
+							 * (that is, the bound at off2 + 1) to get the
+							 * index of that partition.
+							 */
+							if (boundinfo->indexes[off2] < 0)
+								with = boundinfo->indexes[off2 + 1];
+							else
+								with = boundinfo->indexes[off2];
 						}
 					}
 					else
 					{
+						/*
+						 * Equal has been set to true and there is no "gap"
+						 * between the bound at off1 and that at off1 + 1, so
+						 * the new partition will overlap some partition. In
+						 * the former case, the new lower bound is found to be
+						 * equal to the bound at off1, which could only ever
+						 * be true if the latter is the lower bound of some
+						 * partition.  It's clear in such a case that the new
+						 * partition overlaps that partition, whose index we
+						 * get using its upper bound (that is, using the bound
+						 * at off1 + 1).
+						 */
 						overlap = true;
 						with = boundinfo->indexes[off1 + 1];
 					}
@@ -1957,8 +1988,8 @@ partition_bound_cmp(PartitionKey key, PartitionBoundInfo boundinfo,
 }
 
 /*
- * Binary search on a collection of partition bounds. Returns greatest index
+ * Binary search on a collection of partition bounds. Returns greatest
- * of bound in array boundinfo->datums which is less or equal with *probe.
+ * bound in array boundinfo->datums which is less than or equal to *probe
  * If all bounds in the array are greater than *probe, -1 is returned.
  *
  * *probe could either be a partition bound or a Datum array representing
@@ -1990,6 +2021,9 @@ partition_bound_bsearch(PartitionKey key, PartitionBoundInfo boundinfo,
 		{
 			lo = mid;
 			*is_equal = (cmpval == 0);
+
+			if (*is_equal)
+				break;
 		}
 		else
 			hi = mid - 1;

src/test/regress/expected/create_table.out

@@ -551,6 +551,12 @@ ERROR:  partition "fail_part" would overlap partition "part0"
 CREATE TABLE part1 PARTITION OF range_parted2 FOR VALUES FROM (1) TO (10);
 CREATE TABLE fail_part PARTITION OF range_parted2 FOR VALUES FROM (9) TO (unbounded);
 ERROR:  partition "fail_part" would overlap partition "part1"
+CREATE TABLE part2 PARTITION OF range_parted2 FOR VALUES FROM (20) TO (30);
+CREATE TABLE part3 PARTITION OF range_parted2 FOR VALUES FROM (30) TO (40);
+CREATE TABLE fail_part PARTITION OF range_parted2 FOR VALUES FROM (10) TO (30);
+ERROR:  partition "fail_part" would overlap partition "part2"
+CREATE TABLE fail_part PARTITION OF range_parted2 FOR VALUES FROM (10) TO (50);
+ERROR:  partition "fail_part" would overlap partition "part3"
 -- now check for multi-column range partition key
 CREATE TABLE range_parted3 (
 	a int,
@@ -655,13 +661,15 @@ table part_c depends on table parted
 table part_c_1_10 depends on table part_c
 HINT:  Use DROP ... CASCADE to drop the dependent objects too.
 DROP TABLE parted, list_parted, range_parted, list_parted2, range_parted2, range_parted3 CASCADE;
-NOTICE:  drop cascades to 14 other objects
+NOTICE:  drop cascades to 16 other objects
 DETAIL:  drop cascades to table part00
 drop cascades to table part10
 drop cascades to table part11
 drop cascades to table part12
 drop cascades to table part0
 drop cascades to table part1
+drop cascades to table part2
+drop cascades to table part3
 drop cascades to table part_null_z
 drop cascades to table part_ab
 drop cascades to table part_1

src/test/regress/sql/create_table.sql

@@ -519,6 +519,10 @@ CREATE TABLE part0 PARTITION OF range_parted2 FOR VALUES FROM (unbounded) TO (1)
 CREATE TABLE fail_part PARTITION OF range_parted2 FOR VALUES FROM (unbounded) TO (2);
 CREATE TABLE part1 PARTITION OF range_parted2 FOR VALUES FROM (1) TO (10);
 CREATE TABLE fail_part PARTITION OF range_parted2 FOR VALUES FROM (9) TO (unbounded);
+CREATE TABLE part2 PARTITION OF range_parted2 FOR VALUES FROM (20) TO (30);
+CREATE TABLE part3 PARTITION OF range_parted2 FOR VALUES FROM (30) TO (40);
+CREATE TABLE fail_part PARTITION OF range_parted2 FOR VALUES FROM (10) TO (30);
+CREATE TABLE fail_part PARTITION OF range_parted2 FOR VALUES FROM (10) TO (50);
 
 -- now check for multi-column range partition key
 CREATE TABLE range_parted3 (