Use hypertable selectedCols for building scan on compressed chunk

Since we do not adjust selectedCols for the Chunk RangeTblEntry
attribute numbers in selectedCols will be wrong if attribute numbers
on hypertable and chunk differ. This patch changes the target list
creation to use the hypertable selectedCols and look up names
on the hypertable to work around this.

tsl/src/decompress_chunk/decompress_chunk.c

@@ -65,6 +65,7 @@ ts_decompress_chunk_path_create(PlannerInfo *root, RelOptInfo *rel, Hypertable *
 	Index chunk_index = rel->relid;
 	Chunk *compressed_chunk = ts_chunk_get_by_id(chunk->fd.compressed_chunk_id, 0, true);
 	Oid compressed_relid = compressed_chunk->table_id;
+	AppendRelInfo *appinfo;
 
 	path = (DecompressChunkPath *) newNode(sizeof(DecompressChunkPath), T_CustomPath);
 
@@ -73,6 +74,14 @@ ts_decompress_chunk_path_create(PlannerInfo *root, RelOptInfo *rel, Hypertable *
 	path->hypertable_id = ht->fd.id;
 	path->compression_info = get_hypertablecompression_info(ht->fd.id);
 
+#if PG96 || PG10
+	appinfo = find_childrel_appendrelinfo(root, rel);
+#else
+	appinfo = root->append_rel_array[rel->relid];
+#endif
+
+	path->ht_rte = planner_rt_fetch(appinfo->parent_relid, root);
+
 	path->cpath.path.pathtype = T_CustomScan;
 	path->cpath.path.parent = rel;
 	path->cpath.path.pathtarget = rel->reltarget;
@@ -210,23 +219,22 @@ get_column_compressioninfo(List *hypertable_compression_info, char *column_name)
 		if (namestrcmp(&fd->attname, column_name) == 0)
 			return fd;
 	}
-
 	elog(ERROR, "No compression information for column \"%s\" found.", column_name);
 
 	pg_unreachable();
 }
 
 /*
- * find matching column attno for compressed chunk
+ * find matching column attno for compressed chunk based on hypertable attno
  *
  * since we dont want aliasing to interfere we lookup directly in catalog
  * instead of using RangeTblEntry
  */
 AttrNumber
-get_compressed_attno(DecompressChunkPath *dcpath, AttrNumber chunk_attno)
+get_compressed_attno(DecompressChunkPath *dcpath, AttrNumber ht_attno)
 {
 	AttrNumber compressed_attno;
-	char *chunk_col = get_attname_compat(dcpath->chunk_rte->relid, chunk_attno, false);
+	char *chunk_col = get_attname_compat(dcpath->ht_rte->relid, ht_attno, false);
 	compressed_attno = get_attnum(dcpath->compressed_rte->relid, chunk_col);
 
 	if (compressed_attno == InvalidAttrNumber)

tsl/src/decompress_chunk/decompress_chunk.h

@@ -20,6 +20,7 @@ typedef struct DecompressChunkPath
 	RelOptInfo *compressed_rel;
 	RangeTblEntry *chunk_rte;
 	RangeTblEntry *compressed_rte;
+	RangeTblEntry *ht_rte;
 	List *varattno_map;
 	int hypertable_id;
 	List *compression_info;

tsl/src/decompress_chunk/planner.c

@@ -69,24 +69,28 @@ lookup_compressed_data_oid()
 }
 
 static TargetEntry *
-make_compressed_scan_targetentry(DecompressChunkPath *path, Relation r, AttrNumber chunk_attno,
-								 int tle_index)
+make_compressed_scan_targetentry(DecompressChunkPath *path, AttrNumber ht_attno, int tle_index)
 {
 	Var *scan_var;
-	if (chunk_attno > 0)
+	if (ht_attno > 0)
 	{
-		TupleDesc desc = RelationGetDescr(r);
-		Form_pg_attribute attribute = TupleDescAttr(desc, AttrNumberGetAttrOffset(chunk_attno));
+		char *ht_attname = get_attname_compat(path->ht_rte->relid, ht_attno, false);
 		FormData_hypertable_compression *ht_info =
-			get_column_compressioninfo(path->compression_info, NameStr(attribute->attname));
-		AttrNumber scan_varattno = get_compressed_attno(path, chunk_attno);
+			get_column_compressioninfo(path->compression_info, ht_attname);
+		AttrNumber scan_varattno = get_compressed_attno(path, ht_attno);
+		AttrNumber chunk_attno = get_attnum(path->chunk_rte->relid, ht_attname);
 
 		if (ht_info->algo_id == 0)
-			scan_var =
-				makeVar(path->compressed_rel->relid, scan_varattno, attribute->atttypid, -1, 0, 0);
+			scan_var = makeVar(path->compressed_rel->relid,
+							   scan_varattno,
+							   get_atttype(path->ht_rte->relid, ht_attno),
+							   -1,
+							   0,
+							   0);
 		else
 			scan_var =
 				makeVar(path->compressed_rel->relid, scan_varattno, COMPRESSEDDATAOID, -1, 0, 0);
+		path->varattno_map = lappend_int(path->varattno_map, chunk_attno);
 	}
 	else
 	{
@@ -95,27 +99,32 @@ make_compressed_scan_targetentry(DecompressChunkPath *path, Relation r, AttrNumb
 			elog(ERROR, "lookup failed for column \"%s\"", META_COUNT_COLUMN_NAME);
 
 		scan_var = makeVar(path->compressed_rel->relid, count_attno, INT4OID, -1, 0, 0);
+		path->varattno_map = lappend_int(path->varattno_map, 0);
 	}
 	return makeTargetEntry((Expr *) scan_var, tle_index, NULL, false);
 }
 
 /*
  * build targetlist for scan on compressed chunk
+ *
+ * Since we do not adjust selectedCols in RangeTblEntry for chunks
+ * we use selectedCols from the hypertable RangeTblEntry to
+ * build the target list for the compressed chunk and adjust
+ * attno accordingly
  */
 static List *
-build_scan_tlist(DecompressChunkPath *dcpath)
+build_scan_tlist(DecompressChunkPath *path)
 {
 	List *scan_tlist = NIL;
-	List *varattno_map = NIL;
-	Bitmapset *attrs_used = dcpath->chunk_rte->selectedCols;
+	Bitmapset *attrs_used = path->ht_rte->selectedCols;
 	TargetEntry *tle;
 	int bit;
-	Relation r = heap_open(dcpath->chunk_rte->relid, NoLock);
+
+	path->varattno_map = NIL;
 
 	/* add count column */
-	tle = make_compressed_scan_targetentry(dcpath, r, 0, list_length(scan_tlist) + 1);
+	tle = make_compressed_scan_targetentry(path, 0, list_length(scan_tlist) + 1);
 	scan_tlist = lappend(scan_tlist, tle);
-	varattno_map = lappend_int(varattno_map, 0);
 
 	bit = bms_next_member(attrs_used, -1);
 	if (bit > 0 && bit + FirstLowInvalidHeapAttributeNumber < 0)
@@ -125,24 +134,20 @@ build_scan_tlist(DecompressChunkPath *dcpath)
 	if (bms_is_member(0 - FirstLowInvalidHeapAttributeNumber, attrs_used))
 	{
 		ListCell *lc;
-		AttrNumber chunk_attno = 0;
+		AttrNumber ht_attno = 0;
 
-		foreach (lc, dcpath->chunk_rte->eref->colnames)
+		foreach (lc, path->ht_rte->eref->colnames)
 		{
 			Value *chunk_col = (Value *) lfirst(lc);
-			chunk_attno++;
+			ht_attno++;
 
 			/*
 			 * dropped columns have empty string
 			 */
 			if (IsA(lfirst(lc), String) && strlen(chunk_col->val.str) > 0)
 			{
-				tle = make_compressed_scan_targetentry(dcpath,
-													   r,
-													   chunk_attno,
-													   list_length(scan_tlist) + 1);
+				tle = make_compressed_scan_targetentry(path, ht_attno, list_length(scan_tlist) + 1);
 				scan_tlist = lappend(scan_tlist, tle);
-				varattno_map = lappend_int(varattno_map, chunk_attno);
 			}
 		}
 	}
@@ -157,24 +162,13 @@ build_scan_tlist(DecompressChunkPath *dcpath)
 		for (bit = bms_next_member(attrs_used, -1); bit > 0; bit = bms_next_member(attrs_used, bit))
 		{
 			/* bits are offset by FirstLowInvalidHeapAttributeNumber */
-			AttrNumber uc_attno = bit + FirstLowInvalidHeapAttributeNumber;
+			AttrNumber ht_attno = bit + FirstLowInvalidHeapAttributeNumber;
 
-			tle =
-				make_compressed_scan_targetentry(dcpath, r, uc_attno, list_length(scan_tlist) + 1);
+			tle = make_compressed_scan_targetentry(path, ht_attno, list_length(scan_tlist) + 1);
 			scan_tlist = lappend(scan_tlist, tle);
-			varattno_map = lappend_int(varattno_map, uc_attno);
 		}
 	}
 
-	dcpath->varattno_map = varattno_map;
-
-	/*
-	 * Drop the rel refcount, but keep the access lock till end of transaction
-	 * so that the table can't be deleted or have its schema modified
-	 * underneath us.
-	 */
-	heap_close(r, NoLock);
-
 	return scan_tlist;
 }