Fix building of large (bigger than shared_buffers) hash indexes.

When the index is predicted to need more than NBuffers buckets,
CREATE INDEX attempts to sort the index entries by hash key before
insertion, so as to reduce thrashing.  This code path got broken by
commit 9f03ca915196dfc8, which overlooked that _hash_form_tuple() is not
just an alias for index_form_tuple().  The index got built anyway, but
with garbage data, so that searches for pre-existing tuples always
failed.  Fix by refactoring to separate construction of the indexable
data from calling index_form_tuple().

Per bug #14210 from Daniel Newman.  Back-patch to 9.5 where the
bug was introduced.

Report: <20160623162507.17237.39471@wrigleys.postgresql.org>

1 files changed, 27 insertions, 17 deletions

diff --git a/src/backend/access/hash/hashutil.c b/src/backend/access/hash/hashutil.c
index 3d662164749..9f8fcc96a3b 100644
--- a/src/backend/access/hash/hashutil.c
+++ b/src/backend/access/hash/hashutil.c
@@ -248,27 +248,37 @@ _hash_get_indextuple_hashkey(IndexTuple itup)
 }
 
 /*
- * _hash_form_tuple - form an index tuple containing hash code only
+ * _hash_convert_tuple - convert raw index data to hash key
+ *
+ * Inputs: values and isnull arrays for the user data column(s)
+ * Outputs: values and isnull arrays for the index tuple, suitable for
+ *		passing to index_form_tuple().
+ *
+ * Returns true if successful, false if not (because there are null values).
+ * On a false result, the given data need not be indexed.
+ *
+ * Note: callers know that the index-column arrays are always of length 1.
+ * In principle, there could be more than one input column, though we do not
+ * currently support that.
  */
-IndexTuple
-_hash_form_tuple(Relation index, Datum *values, bool *isnull)
+bool
+_hash_convert_tuple(Relation index,
+					Datum *user_values, bool *user_isnull,
+					Datum *index_values, bool *index_isnull)
 {
-	IndexTuple	itup;
 	uint32		hashkey;
-	Datum		hashkeydatum;
-	TupleDesc	hashdesc;
 
-	if (isnull[0])
-		hashkeydatum = (Datum) 0;
-	else
-	{
-		hashkey = _hash_datum2hashkey(index, values[0]);
-		hashkeydatum = UInt32GetDatum(hashkey);
-	}
-	hashdesc = RelationGetDescr(index);
-	Assert(hashdesc->natts == 1);
-	itup = index_form_tuple(hashdesc, &hashkeydatum, isnull);
-	return itup;
+	/*
+	 * We do not insert null values into hash indexes.  This is okay because
+	 * the only supported search operator is '=', and we assume it is strict.
+	 */
+	if (user_isnull[0])
+		return false;
+
+	hashkey = _hash_datum2hashkey(index, user_values[0]);
+	index_values[0] = UInt32GetDatum(hashkey);
+	index_isnull[0] = false;
+	return true;
 }
 
 /*