Simplify dealing with attnos during decompression

We fetch key column attribute numbers from indexes
on uncompressed chunks. These should not contain
system attribute numbers so there is no point in
adding/subtracting FirstLowInvalidHeapAttributeNumber.

Author: antekresic

tsl/src/compression/compression_dml.c

@@ -805,12 +805,13 @@ get_batch_keys_for_unique_constraints(const ChunkInsertState *cis, Relation rela
 		 */
 		for (int i = 0; i < indexDesc->rd_index->indnkeyatts; i++)
 		{
-			int attno = indexDesc->rd_index->indkey.values[i];
+			AttrNumber attno = indexDesc->rd_index->indkey.values[i];
 			/* We are not interested in expression columns which will have attno = 0 */
 			if (!attno)
 				continue;
 
-			idx_attrs = bms_add_member(idx_attrs, attno - FirstLowInvalidHeapAttributeNumber);
+			Assert(AttrNumberIsForUserDefinedAttr(attno));
+			idx_attrs = bms_add_member(idx_attrs, attno);
 		}
 		index_close(indexDesc, AccessShareLock);
 
@@ -1351,11 +1352,9 @@ key_column_is_null(tuple_filtering_constraints *constraints, Relation chunk_rel,
 	if (!constraints->covered || constraints->nullsnotdistinct)
 		return false;
 
-	int i = -1;
-	while ((i = bms_next_member(constraints->key_columns, i)) > 0)
+	AttrNumber chunk_attno = -1;
+	while ((chunk_attno = bms_next_member(constraints->key_columns, chunk_attno)) > 0)
 	{
-		AttrNumber chunk_attno = i + FirstLowInvalidHeapAttributeNumber;
-
 		/*
 		 * slot has the physical layout of the hypertable, so we need to
 		 * get the attribute number of the hypertable for the column.

tsl/src/compression/compression_dml.h

@@ -13,6 +13,11 @@
 
 typedef struct tuple_filtering_constraints
 {
+	/*
+	 * All key column heap attribute numbers on uncompressed chunk.
+	 * We shouldn't be dealing with system columns so no need to
+	 * add/subtract FirstLowInvalidHeapAttributeNumber from these.
+	 */
 	Bitmapset *key_columns;
 	/*
 	 * The covered flag is set to true if we have a single constraint that is covered

tsl/src/compression/compression_scankey.c

@@ -45,10 +45,9 @@ build_mem_scankeys_from_slot(Oid ht_relid, CompressionSettings *settings, Relati
 
 	scankeys = palloc(sizeof(ScanKeyData) * bms_num_members(constraints->key_columns));
 
-	int i = -1;
-	while ((i = bms_next_member(constraints->key_columns, i)) > 0)
+	AttrNumber attno = -1;
+	while ((attno = bms_next_member(constraints->key_columns, attno)) > 0)
 	{
-		AttrNumber attno = i + FirstLowInvalidHeapAttributeNumber;
 		bool isnull;
 
 		/*
@@ -125,10 +124,9 @@ build_heap_scankeys(Oid hypertable_relid, Relation in_rel, Relation out_rel,
 	if (!bms_is_empty(key_columns))
 	{
 		scankeys = palloc0(bms_num_members(key_columns) * 2 * sizeof(ScanKeyData));
-		int i = -1;
-		while ((i = bms_next_member(key_columns, i)) > 0)
+		AttrNumber attno = -1;
+		while ((attno = bms_next_member(key_columns, attno)) > 0)
 		{
-			AttrNumber attno = i + FirstLowInvalidHeapAttributeNumber;
 			char *attname = get_attname(out_rel->rd_id, attno, false);
 			bool isnull;
 			AttrNumber ht_attno = get_attnum(hypertable_relid, attname);
@@ -322,8 +320,7 @@ build_index_scankeys_using_slot(Oid hypertable_relid, Relation in_rel, Relation
 			AttrNumber idx_attnum = AttrOffsetGetAttrNumber(i);
 			AttrNumber in_attnum = index_rel->rd_index->indkey.values[i];
 			const NameData *attname = attnumAttName(in_rel, in_attnum);
-			AttrNumber column_attno =
-				get_attnum(out_rel->rd_id, NameStr(*attname)) - FirstLowInvalidHeapAttributeNumber;
+			AttrNumber column_attno = get_attnum(out_rel->rd_id, NameStr(*attname));
 
 			/* Make sure we find columns in key columns in order to select the right index */
 			if (!bms_is_member(column_attno, key_columns))