Fix segmentby typmod and collation of compressed chunks

.unreleased/pr_6332

@@ -0,0 +1 @@
+Fixes: #6332 Fix typmod and collation for segmentby columns

sql/updates/latest-dev.sql

@@ -403,3 +403,42 @@ BEGIN
   END LOOP;
 END;
 $$ LANGUAGE PLPGSQL;
+
+-- fix atttypmod and attcollation for segmentby columns
+DO $$
+DECLARE
+  htc_id INTEGER;
+  htc REGCLASS;
+  _attname NAME;
+  _atttypmod INTEGER;
+  _attcollation OID;
+BEGIN
+  -- find any segmentby columns where typmod and collation in
+  -- the compressed hypertable does not match the uncompressed
+  -- hypertable values
+  FOR htc_id, htc, _attname, _atttypmod, _attcollation IN
+    SELECT cat.htc_id, cat.htc, pga.attname, ht_mod, ht_coll
+    FROM pg_attribute pga
+    INNER JOIN
+    (
+      SELECT
+        htc.id AS htc_id,
+        format('%I.%I',htc.schema_name,htc.table_name) AS htc,
+        att_ht.atttypmod AS ht_mod,
+        att_ht.attcollation AS ht_coll,
+        c.attname
+      FROM _timescaledb_catalog.hypertable_compression c
+      INNER JOIN _timescaledb_catalog.hypertable ht ON ht.id=c.hypertable_id
+      INNER JOIN pg_attribute att_ht ON att_ht.attname = c.attname AND att_ht.attrelid = format('%I.%I',ht.schema_name,ht.table_name)::regclass
+      INNER JOIN _timescaledb_catalog.hypertable htc ON htc.id=ht.compressed_hypertable_id
+      WHERE c.segmentby_column_index > 0
+    ) cat ON cat.htc::regclass = pga.attrelid AND cat.attname = pga.attname
+    WHERE pga.atttypmod <> ht_mod OR pga.attcollation <> ht_coll
+  LOOP
+    -- fix typmod and collation for the compressed hypertable and all compressed chunks
+    UPDATE pg_attribute SET atttypmod = _atttypmod, attcollation = _attcollation WHERE attname = _attname AND attrelid IN (
+      SELECT format('%I.%I',schema_name,table_name)::regclass from _timescaledb_catalog.chunk WHERE hypertable_id = htc_id AND NOT dropped UNION ALL SELECT htc
+    );
+  END LOOP;
+END
+$$;

tsl/src/nodes/decompress_chunk/planner.c

@@ -177,30 +177,9 @@ build_decompression_map(PlannerInfo *root, DecompressChunkPath *path, List *scan
 			/*
 			 * Normal column, not a metadata column.
 			 */
-			AttrNumber hypertable_attno = get_attnum(path->info->ht_rte->relid, column_name);
 			AttrNumber chunk_attno = get_attnum(path->info->chunk_rte->relid, column_name);
-			Assert(hypertable_attno != InvalidAttrNumber);
 			Assert(chunk_attno != InvalidAttrNumber);
 
-			/*
-			 * The versions older than this commit didn't set up the proper
-			 * collation and typmod for segmentby columns in compressed chunks,
-			 * so we have to determine them from the main hypertable.
-			 * Additionally, we have to set the proper type for the compressed
-			 * columns. It would be cool to get rid of this code someday and
-			 * just use the types from the compressed chunk, but the problem is
-			 * that we have to support the chunks created by the older versions
-			 * of TimescaleDB.
-			 */
-			if (compression_info->algo_id == _INVALID_COMPRESSION_ALGORITHM)
-			{
-				get_atttypetypmodcoll(path->info->ht_rte->relid,
-									  hypertable_attno,
-									  &var->vartype,
-									  &var->vartypmod,
-									  &var->varcollid);
-			}
-
 			if (bms_is_member(0 - FirstLowInvalidHeapAttributeNumber, chunk_attrs_needed))
 			{
 				/*