Block merging of frozen chunks

It should not be possible to merge a frozen chunk since it is used to
tier chunks. If the chunk is merged, it might no longer exist when the
tiering happens.

.unreleased/pr_7665

@@ -0,0 +1 @@
+Fixes: #7665 Block merging of frozen chunks

src/chunk.c

@@ -3406,7 +3406,7 @@ ts_chunk_unset_frozen(Chunk *chunk)
 }
 
 bool
-ts_chunk_is_frozen(Chunk *chunk)
+ts_chunk_is_frozen(const Chunk *chunk)
 {
 	return ts_flags_are_set_32(chunk->fd.status, CHUNK_STATUS_FROZEN);
 }

src/chunk.h

@@ -200,7 +200,7 @@ extern TSDLLEXPORT bool ts_chunk_set_partial(Chunk *chunk);
 extern TSDLLEXPORT bool ts_chunk_set_unordered(Chunk *chunk);
 extern TSDLLEXPORT bool ts_chunk_set_frozen(Chunk *chunk);
 extern TSDLLEXPORT bool ts_chunk_unset_frozen(Chunk *chunk);
-extern TSDLLEXPORT bool ts_chunk_is_frozen(Chunk *chunk);
+extern TSDLLEXPORT bool ts_chunk_is_frozen(const Chunk *chunk);
 extern TSDLLEXPORT bool ts_chunk_set_compressed_chunk(Chunk *chunk, int32 compressed_chunk_id);
 extern TSDLLEXPORT bool ts_chunk_clear_compressed_chunk(Chunk *chunk);
 extern TSDLLEXPORT void ts_chunk_drop(const Chunk *chunk, DropBehavior behavior, int32 log_level);

tsl/src/chunk.c

@@ -12,7 +12,6 @@
 #include <access/tableam.h>
 #include <access/transam.h>
 #include <access/xact.h>
-#include <c.h>
 #include <catalog/catalog.h>
 #include <catalog/dependency.h>
 #include <catalog/heap.h>
@@ -893,6 +892,14 @@ chunk_merge_chunks(PG_FUNCTION_ARGS)
 					 errmsg("merging compressed chunks is not yet supported"),
 					 errhint("Decompress the chunks before merging.")));
 
+		if (ts_chunk_is_frozen(chunk))
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("cannot merge frozen chunk \"%s.%s\" scheduled for tiering",
+							NameStr(chunk->fd.schema_name),
+							NameStr(chunk->fd.table_name)),
+					 errhint("Untier the chunk before merging.")));
+
 		if (hypertable_id == INVALID_HYPERTABLE_ID)
 			hypertable_id = chunk->fd.hypertable_id;
 		else if (hypertable_id != chunk->fd.hypertable_id)

tsl/test/expected/merge_chunks.out

@@ -353,6 +353,23 @@ ERROR:  cannot merge OSM chunks
 reset role;
 update _timescaledb_catalog.chunk ch set osm_chunk = false where table_name = '_hyper_1_1_chunk';
 set role :ROLE_DEFAULT_PERM_USER;
+-- Merge frozen chunks
+select _timescaledb_functions.freeze_chunk('_timescaledb_internal._hyper_1_1_chunk');
+ freeze_chunk 
+--------------
+ t
+(1 row)
+
+call merge_chunks('_timescaledb_internal._hyper_1_1_chunk', '_timescaledb_internal._hyper_1_2_chunk');
+ERROR:  cannot merge frozen chunk "_timescaledb_internal._hyper_1_1_chunk" scheduled for tiering
+call merge_chunks('_timescaledb_internal._hyper_1_2_chunk', '_timescaledb_internal._hyper_1_1_chunk');
+ERROR:  cannot merge frozen chunk "_timescaledb_internal._hyper_1_1_chunk" scheduled for tiering
+select _timescaledb_functions.unfreeze_chunk('_timescaledb_internal._hyper_1_1_chunk');
+ unfreeze_chunk 
+----------------
+ t
+(1 row)
+
 \set ON_ERROR_STOP 1
 -- Set seed to consistently generate same data and same set of chunks
 select setseed(0.2);

tsl/test/sql/merge_chunks.sql

@@ -218,6 +218,12 @@ reset role;
 update _timescaledb_catalog.chunk ch set osm_chunk = false where table_name = '_hyper_1_1_chunk';
 set role :ROLE_DEFAULT_PERM_USER;
 
+-- Merge frozen chunks
+select _timescaledb_functions.freeze_chunk('_timescaledb_internal._hyper_1_1_chunk');
+call merge_chunks('_timescaledb_internal._hyper_1_1_chunk', '_timescaledb_internal._hyper_1_2_chunk');
+call merge_chunks('_timescaledb_internal._hyper_1_2_chunk', '_timescaledb_internal._hyper_1_1_chunk');
+select _timescaledb_functions.unfreeze_chunk('_timescaledb_internal._hyper_1_1_chunk');
+
 \set ON_ERROR_STOP 1