Support sub-second intervals in hierarchical caggs

Previously we used date_part("epoch", interval) and integer division
internally to determine whether the top cagg's interval is a
multiple of its parent's.
This led to precision loss and wrong results
in the case of intervals with sub-second components.

Fixed by using the `ts_interval_value_to_internal` function to convert
intervals to appropriate integer representation for division.

Fixes #5277

CHANGELOG.md

@@ -13,6 +13,7 @@ accidentally triggering the load of a previous DB version.**
 * #5317 Fix some incorrect memory handling
 * #5367 Rename columns in old-style continuous aggregates
 * #5384 Fix Hierarchical Continuous Aggregates chunk_interval_size
+* #5304 Support sub-second intervals in hierarchical caggs
 
 **Thanks**
 * @Medvecrab for discovering an issue with copying NameData when forming heap tuples.

tsl/src/continuous_aggs/create.c

@@ -1128,7 +1128,7 @@ cagg_query_supported(const Query *query, StringInfo hint, StringInfo detail, con
 static inline int64
 get_bucket_width(CAggTimebucketInfo bucket_info)
 {
-	int64 width = 0;
+	float8 width = 0;
 
 	/* Calculate the width. */
 	switch (bucket_info.bucket_width_type)
@@ -1151,11 +1151,9 @@ get_bucket_width(CAggTimebucketInfo bucket_info)
 				bucket_info.interval->day = bucket_info.interval->month * DAYS_PER_MONTH;
 				bucket_info.interval->month = 0;
 			}
-			Datum epoch = DirectFunctionCall2(interval_part,
-											  PointerGetDatum(cstring_to_text("epoch")),
-											  IntervalPGetDatum(bucket_info.interval));
-			/* Cast float8 to int8. */
-			width = DatumGetInt64(DirectFunctionCall1(dtoi8, epoch));
+
+			/* Convert Interval to int64 */
+			width = ts_interval_value_to_internal(IntervalPGetDatum(bucket_info.interval), INTERVALOID);
 			break;
 		}
 		default:
@@ -1546,9 +1544,9 @@ cagg_validate_query(const Query *query, const bool finalized, const char *cagg_s
 		if (bucket_width_parent != 0)
 		{
 			if (bucket_width_parent > bucket_width && bucket_width != 0)
-				is_multiple_of_parent = ((bucket_width_parent % bucket_width) == 0);
+				is_multiple_of_parent = (fmod(bucket_width_parent, bucket_width) == 0);
 			else
-				is_multiple_of_parent = ((bucket_width % bucket_width_parent) == 0);
+				is_multiple_of_parent = (fmod(bucket_width, bucket_width_parent) == 0);
 		}
 
 		/* Proceed with validation errors. */