Do not recompress segmentwise when default order by is empty (#7789)

When we have compression where default order by is set to "", we cannot
do meaningful segmentwise recompression. Therefore we will return error
when segmentwise recompression is requested directly and will do full
recompression when general compression is requested.

Fixes: #7748

.unreleased/pr_7789

@@ -0,0 +1,2 @@
+Implements: #7789 Do not recompress segmentwise when default order by is empty
+Fixes: #7748 Crash in the segmentwise recompression

tsl/src/compression/api.c

@@ -940,12 +940,14 @@ tsl_compress_chunk_wrapper(Chunk *chunk, bool if_not_compressed, bool recompress
 
 	if (ts_chunk_is_compressed(chunk))
 	{
+		CompressionSettings *chunk_settings = ts_compression_settings_get(chunk->table_id);
+		bool valid_orderby_settings = chunk_settings->fd.orderby;
 		if (recompress)
 		{
 			CompressionSettings *ht_settings = ts_compression_settings_get(chunk->hypertable_relid);
-			CompressionSettings *chunk_settings = ts_compression_settings_get(chunk->table_id);
 
-			if (!ts_compression_settings_equal(ht_settings, chunk_settings))
+			if (!valid_orderby_settings ||
+				!ts_compression_settings_equal(ht_settings, chunk_settings))
 			{
 				decompress_chunk_impl(chunk, false);
 				compress_chunk_impl(chunk->hypertable_relid, chunk->table_id);
@@ -962,17 +964,21 @@ tsl_compress_chunk_wrapper(Chunk *chunk, bool if_not_compressed, bool recompress
 			return uncompressed_chunk_id;
 		}
 
-		if (ts_guc_enable_segmentwise_recompression && ts_chunk_is_partial(chunk) &&
-			get_compressed_chunk_index_for_recompression(chunk))
+		if (ts_guc_enable_segmentwise_recompression && valid_orderby_settings &&
+			ts_chunk_is_partial(chunk) && get_compressed_chunk_index_for_recompression(chunk))
 		{
 			uncompressed_chunk_id = recompress_chunk_segmentwise_impl(chunk);
 		}
 		else
 		{
-			if (!ts_guc_enable_segmentwise_recompression)
+			if (!ts_guc_enable_segmentwise_recompression || !valid_orderby_settings)
 				elog(NOTICE,
-					 "segmentwise recompression is disabled, performing full recompression on "
+					 "segmentwise recompression is disabled%s, performing full "
+					 "recompression on "
 					 "chunk \"%s.%s\"",
+					 (ts_guc_enable_segmentwise_recompression && !valid_orderby_settings ?
+						  " due to no order by" :
+						  ""),
 					 NameStr(chunk->fd.schema_name),
 					 NameStr(chunk->fd.table_name));
 			decompress_chunk_impl(chunk, false);

tsl/src/compression/create.c

@@ -1142,10 +1142,16 @@ compression_setting_orderby_get_default(Hypertable *ht, ArrayType *segmentby)
 	else
 		orderby = "";
 
-	elog(NOTICE,
-		 "default order by for hypertable \"%s\" is set to \"%s\"",
-		 get_rel_name(ht->main_table_relid),
-		 orderby);
+	if (*orderby == '\0')
+		ereport(NOTICE,
+				(errmsg("default order by for hypertable \"%s\" is set to \"\"",
+						get_rel_name(ht->main_table_relid))),
+				errdetail("Segmentwise recompression will be disabled"));
+	else
+		elog(NOTICE,
+			 "default order by for hypertable \"%s\" is set to \"%s\"",
+			 get_rel_name(ht->main_table_relid),
+			 orderby);
 
 	elog(LOG_SERVER_ONLY,
 		 "order_by default: hypertable=\"%s\" clauses=\"%s\" function=\"%s.%s\" confidence=%d",

tsl/src/compression/recompress.c

@@ -18,6 +18,7 @@
 #include "compression.h"
 #include "compression_dml.h"
 #include "create.h"
+#include "debug_assert.h"
 #include "guc.h"
 #include "hypercore/hypercore_handler.h"
 #include "hypercore/utils.h"
@@ -83,6 +84,15 @@ tsl_recompress_chunk_segmentwise(PG_FUNCTION_ARGS)
 							"enable it by first setting "
 							"timescaledb.enable_segmentwise_recompression to on")));
 		}
+		CompressionSettings *settings = ts_compression_settings_get(uncompressed_chunk_id);
+		if (!settings->fd.orderby)
+		{
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("segmentwise recompression cannot be applied for "
+							"compression with no "
+							"order by")));
+		}
 		uncompressed_chunk_id = recompress_chunk_segmentwise_impl(chunk);
 	}
 
@@ -112,6 +122,10 @@ recompress_chunk_segmentwise_impl(Chunk *uncompressed_chunk)
 	Chunk *compressed_chunk = ts_chunk_get_by_id(uncompressed_chunk->fd.compressed_chunk_id, true);
 	CompressionSettings *settings = ts_compression_settings_get(uncompressed_chunk->table_id);
 
+	/* We should not do segment-wise recompression with empty orderby, see #7748
+	 */
+	Ensure(settings->fd.orderby, "empty order by, cannot recompress segmentwise");
+
 	/* new status after recompress should simply be compressed (1)
 	 * It is ok to update this early on in the transaction as it keeps a lock
 	 * on the updated tuple in the CHUNK table potentially preventing other transaction

tsl/test/expected/recompress_chunk_segmentwise.out

@@ -647,13 +647,51 @@ INFO:  Using index "compress_hyper_19_20_chunk__ts_meta_min_1__ts_meta_max_1_idx
  _timescaledb_internal._hyper_18_19_chunk
 (1 row)
 
+-- Test behaviour when default order by is empty: should not segmentwise-recompress in this case
+CREATE TABLE no_oby(ts int, c1 int);
+SELECT create_hypertable('no_oby','ts');
+NOTICE:  adding not-null constraint to column "ts"
+  create_hypertable   
+----------------------
+ (20,public,no_oby,t)
+(1 row)
+
+\set VERBOSITY default
+ALTER TABLE no_oby SET (timescaledb.compress, timescaledb.compress_segmentby = 'ts');
+NOTICE:  default order by for hypertable "no_oby" is set to ""
+DETAIL:  Segmentwise recompression will be disabled
+\set VERBOSITY terse
+INSERT INTO no_oby (ts,c1) VALUES (6,6);
+SELECT show_chunks as chunk_to_compress FROM show_chunks('no_oby') LIMIT 1 \gset
+SELECT compress_chunk(:'chunk_to_compress');
+INFO:  using tuplesort to scan rows from "_hyper_20_21_chunk" for compression
+              compress_chunk              
+------------------------------------------
+ _timescaledb_internal._hyper_20_21_chunk
+(1 row)
+
+INSERT INTO no_oby (ts,c1) VALUES (7,7);
+-- Direct segmentwise-recompress request: throw an error
+\set ON_ERROR_STOP 0
+SELECT _timescaledb_functions.recompress_chunk_segmentwise(:'chunk_to_compress');
+ERROR:  segmentwise recompression cannot be applied for compression with no order by
+\set ON_ERROR_STOP 1
+-- Compress wrapper: do full recompress instead of by segment
+SELECT compress_chunk(:'chunk_to_compress');
+NOTICE:  segmentwise recompression is disabled due to no order by, performing full recompression on chunk "_timescaledb_internal._hyper_20_21_chunk"
+INFO:  using tuplesort to scan rows from "_hyper_20_21_chunk" for compression
+              compress_chunk              
+------------------------------------------
+ _timescaledb_internal._hyper_20_21_chunk
+(1 row)
+
 RESET timescaledb.debug_compression_path_info;
 --- Test behaviour when enable_segmentwise_recompression GUC if OFF
 CREATE TABLE guc_test(time timestamptz not null, a int, b int, c int);
 SELECT create_hypertable('guc_test', by_range('time', INTERVAL '1 day'));
  create_hypertable 
 -------------------
- (20,t)
+ (22,t)
 (1 row)
 
 ALTER TABLE guc_test set (timescaledb.compress, timescaledb.compress_segmentby = 'a, b');
@@ -663,7 +701,7 @@ SELECT show_chunks as chunk_to_compress FROM show_chunks('guc_test') LIMIT 1 \gs
 SELECT compress_chunk(:'chunk_to_compress');
               compress_chunk              
 ------------------------------------------
- _timescaledb_internal._hyper_20_21_chunk
+ _timescaledb_internal._hyper_22_24_chunk
 (1 row)
 
 INSERT INTO guc_test VALUES ('2024-10-30 14:14:00.501519-06'::timestamptz, 1, 1, 2);
@@ -675,9 +713,9 @@ ERROR:  segmentwise recompression functionality disabled, enable it by first set
 \set ON_ERROR_STOP 1
 -- When GUC is OFF, entire chunk should be fully uncompressed and compressed instead
 SELECT compress_chunk(:'chunk_to_compress');
-NOTICE:  segmentwise recompression is disabled, performing full recompression on chunk "_timescaledb_internal._hyper_20_21_chunk"
+NOTICE:  segmentwise recompression is disabled, performing full recompression on chunk "_timescaledb_internal._hyper_22_24_chunk"
               compress_chunk              
 ------------------------------------------
- _timescaledb_internal._hyper_20_21_chunk
+ _timescaledb_internal._hyper_22_24_chunk
 (1 row)
 

tsl/test/sql/recompress_chunk_segmentwise.sql

@@ -307,6 +307,25 @@ INSERT INTO noseg VALUES ('2025-01-24 10:54:27.323421-07'::timestamptz, 1, 1, 2)
 -- should recompress chunk using the default index
 SELECT compress_chunk(:'chunk_to_compress');
 
+-- Test behaviour when default order by is empty: should not segmentwise-recompress in this case
+CREATE TABLE no_oby(ts int, c1 int);
+SELECT create_hypertable('no_oby','ts');
+\set VERBOSITY default
+ALTER TABLE no_oby SET (timescaledb.compress, timescaledb.compress_segmentby = 'ts');
+\set VERBOSITY terse
+
+INSERT INTO no_oby (ts,c1) VALUES (6,6);
+SELECT show_chunks as chunk_to_compress FROM show_chunks('no_oby') LIMIT 1 \gset
+SELECT compress_chunk(:'chunk_to_compress');
+
+INSERT INTO no_oby (ts,c1) VALUES (7,7);
+-- Direct segmentwise-recompress request: throw an error
+\set ON_ERROR_STOP 0
+SELECT _timescaledb_functions.recompress_chunk_segmentwise(:'chunk_to_compress');
+\set ON_ERROR_STOP 1
+-- Compress wrapper: do full recompress instead of by segment
+SELECT compress_chunk(:'chunk_to_compress');
+
 RESET timescaledb.debug_compression_path_info;
 
 --- Test behaviour when enable_segmentwise_recompression GUC if OFF