Add support for splitting a chunk

A chunk can be split with a new procedure called split_chunk(). In
this initial version, a chunk can only be split in two given a split
point:

```
call split_chunk('chunk_1', split_at => '2025-03-01 00:00');
```

If no split point is given, the chunk is split in two equal size
partition ranges. The partitioning dimension/column to split along can
also be specified, but only the primary dimension (time) is
supported. Future updates to split_chunk() can add the ability to
split also along other dimensions, e.g., space partitions.

Currently, splitting a chunk takes an AccessExclusiveLock on the chunk
being split. A lock is also taken on the hypertable root to prevent
new chunks being created while the split is ongoing.

Author: erimatnor

.unreleased/pr_7946

@@ -0,0 +1 @@
+Implements: #7946 Add support for splitting a chunk

sql/maintenance_utils.sql

@@ -65,6 +65,13 @@ CREATE OR REPLACE PROCEDURE @[email protected]_chunks(
     chunks REGCLASS[]
 ) LANGUAGE C AS '@MODULE_PATHNAME@', 'ts_merge_chunks';
 
+CREATE OR REPLACE PROCEDURE @[email protected]_chunk(
+    chunk REGCLASS,
+    column_name NAME = NULL,
+    split_at "any" = NULL,
+    verbose bool = false
+) LANGUAGE C AS '@MODULE_PATHNAME@', 'ts_split_chunk';
+
 CREATE OR REPLACE FUNCTION _timescaledb_functions.recompress_chunk_segmentwise(
     uncompressed_chunk REGCLASS,
     if_compressed BOOLEAN = true

sql/updates/latest-dev.sql

@@ -1,4 +1,10 @@
-
 DROP FUNCTION IF EXISTS _timescaledb_internal.create_chunk_table;
 DROP FUNCTION IF EXISTS _timescaledb_functions.create_chunk_table;
 
+-- Split chunk
+CREATE PROCEDURE @[email protected]_chunk(
+    chunk REGCLASS,
+    column_name NAME = NULL,
+    split_at "any" = NULL,
+    verbose bool = false
+) LANGUAGE C AS '@MODULE_PATHNAME@', 'ts_update_placeholder';

sql/updates/reverse-dev.sql

@@ -1,3 +1,5 @@
-
 CREATE FUNCTION _timescaledb_internal.create_chunk_table(hypertable REGCLASS, slices JSONB, schema_name NAME, table_name NAME) RETURNS BOOL AS '@MODULE_PATHNAME@', 'ts_update_placeholder' LANGUAGE C VOLATILE;
 CREATE FUNCTION _timescaledb_functions.create_chunk_table(hypertable REGCLASS, slices JSONB, schema_name NAME, table_name NAME) RETURNS BOOL AS '@MODULE_PATHNAME@', 'ts_update_placeholder' LANGUAGE C VOLATILE;
+
+-- Split chunk
+DROP PROCEDURE IF EXISTS @[email protected]_chunks(chunk REGCLASS, column_name NAME, split_at "any", verbose bool);

src/cross_module_fn.c

@@ -100,6 +100,7 @@ CROSSMODULE_WRAPPER(chunk_unfreeze_chunk);
 CROSSMODULE_WRAPPER(recompress_chunk_segmentwise);
 CROSSMODULE_WRAPPER(get_compressed_chunk_index_for_recompression);
 CROSSMODULE_WRAPPER(merge_chunks);
+CROSSMODULE_WRAPPER(split_chunk);
 
 /* hypercore */
 CROSSMODULE_WRAPPER(is_compressed_tid);
@@ -432,6 +433,7 @@ TSDLLEXPORT CrossModuleFunctions ts_cm_functions_default = {
 	.get_compressed_chunk_index_for_recompression = error_no_default_fn_pg_community,
 	.preprocess_query_tsl = preprocess_query_tsl_default_fn_community,
 	.merge_chunks = error_no_default_fn_pg_community,
+	.split_chunk = error_no_default_fn_pg_community,
 };
 
 TSDLLEXPORT CrossModuleFunctions *ts_cm_functions = &ts_cm_functions_default;

src/cross_module_fn.h

@@ -164,6 +164,7 @@ typedef struct CrossModuleFunctions
 	PGFunction get_compressed_chunk_index_for_recompression;
 	void (*preprocess_query_tsl)(Query *parse, int *cursor_opts);
 	PGFunction merge_chunks;
+	PGFunction split_chunk;
 } CrossModuleFunctions;
 
 extern TSDLLEXPORT CrossModuleFunctions *ts_cm_functions;