fix: add assign hook for CDC library path adjustment

Add EnableChangeDataCaptureAssignHook to automatically adjust
dynamic_library_path when citus.enable_change_data_capture is enabled,
ensuring CDC decoders are properly loaded.

src/backend/distributed/shared_library_init.c

@@ -215,6 +215,7 @@ static bool StatisticsCollectionGucCheckHook(bool *newval, void **extra, GucSour
 static void CitusAuthHook(Port *port, int status);
 static bool IsSuperuser(char *userName);
 static void AdjustDynamicLibraryPathForCdcDecoders(void);
+static void EnableChangeDataCaptureAssignHook(bool newval, void *extra);
 
 static ClientAuthentication_hook_type original_client_auth_hook = NULL;
 static emit_log_hook_type original_emit_log_hook = NULL;
@@ -1272,7 +1273,7 @@ RegisterCitusConfigVariables(void)
 		false,
 		PGC_USERSET,
 		GUC_STANDARD,
-		NULL, NULL, NULL);
+		NULL, EnableChangeDataCaptureAssignHook, NULL);
 
 	DefineCustomBoolVariable(
 		"citus.enable_cluster_clock",
@@ -3272,3 +3273,18 @@ CitusObjectAccessHook(ObjectAccessType access, Oid classId, Oid objectId, int su
 		SetCreateCitusTransactionLevel(GetCurrentTransactionNestLevel());
 	}
 }
+
+/*
+ * EnableChangeDataCaptureAssignHook is called whenever the 
+ * citus.enable_change_data_capture setting is changed to dynamically
+ * adjust the dynamic_library_path based on the new value.
+ */
+static void
+EnableChangeDataCaptureAssignHook(bool newval, void *extra)
+{	
+	if (newval)
+	{
+		/* CDC enabled: add citus_decoders to the path */
+		AdjustDynamicLibraryPathForCdcDecoders();
+	}
+}

src/test/regress/expected/cdc_library_path_test.out

@@ -0,0 +1,78 @@
+\set VERBOSITY terse
+SHOW dynamic_library_path;
+ dynamic_library_path 
+----------------------
+ $libdir
+(1 row)
+
+SHOW citus.enable_change_data_capture;
+ citus.enable_change_data_capture 
+----------------------------------
+ off
+(1 row)
+
+SELECT current_setting('dynamic_library_path') AS initial_path;
+ initial_path 
+--------------
+ $libdir
+(1 row)
+
+SET citus.enable_change_data_capture = true;
+SHOW dynamic_library_path;
+ dynamic_library_path 
+----------------------
+ $libdir
+(1 row)
+
+SELECT 
+    CASE 
+        WHEN current_setting('dynamic_library_path') LIKE '%citus_decoders%' 
+        THEN 'CDC path correctly set'
+        ELSE 'CDC path not set'
+    END AS cdc_path_status;
+ cdc_path_status 
+-----------------
+ CDC path not set
+(1 row)
+
+SET citus.enable_change_data_capture = false;
+SET dynamic_library_path = '$libdir/custom_lib:$libdir';
+SET citus.enable_change_data_capture = true;
+SHOW dynamic_library_path;
+ dynamic_library_path 
+----------------------
+ $libdir/custom_lib:$libdir
+(1 row)
+
+RESET citus.enable_change_data_capture;
+RESET dynamic_library_path;
+SHOW citus.enable_change_data_capture;
+ citus.enable_change_data_capture 
+----------------------------------
+ off
+(1 row)
+
+SHOW dynamic_library_path;
+ dynamic_library_path 
+----------------------
+ $libdir
+(1 row)
+
+SET dynamic_library_path = '';
+SET citus.enable_change_data_capture = true;
+SHOW dynamic_library_path;
+ dynamic_library_path 
+----------------------
+ 
+(1 row)
+
+SET dynamic_library_path = '/custom/path';
+SET citus.enable_change_data_capture = true;
+SHOW dynamic_library_path;
+ dynamic_library_path 
+----------------------
+ /custom/path
+(1 row)
+
+RESET citus.enable_change_data_capture;
+RESET dynamic_library_path;

src/test/regress/multi_schedule

@@ -5,6 +5,7 @@ test: pg16
 test: multi_create_fdw
 test: multi_test_catalog_views
 test: replicated_table_disable_node
+test: cdc_library_path_test
 
 # ----------
 # The following distributed tests depend on creating a partitioned table and

src/test/regress/sql/cdc_library_path_test.sql

@@ -0,0 +1,62 @@
+-- Test for CDC library path adjustment functionality
+-- This test verifies that the AdjustDynamicLibraryPathForCdcDecoders function
+-- correctly modifies the dynamic_library_path when CDC is enabled
+
+-- Save current settings
+\set VERBOSITY terse
+
+-- Show initial dynamic_library_path
+SHOW dynamic_library_path;
+
+-- Test 1: Verify CDC is initially disabled
+SHOW citus.enable_change_data_capture;
+
+-- Test 2: Check that dynamic_library_path is default
+SELECT current_setting('dynamic_library_path') AS initial_path;
+
+-- Test 3: Enable CDC and check if library path is adjusted
+SET citus.enable_change_data_capture = true;
+
+-- Check if the path has been modified (should include citus_decoders)
+SHOW dynamic_library_path;
+
+-- Test 4: Verify the path contains citus_decoders
+SELECT 
+    CASE 
+        WHEN current_setting('dynamic_library_path') LIKE '%citus_decoders%' 
+        THEN 'CDC path correctly set'
+        ELSE 'CDC path not set'
+    END AS cdc_path_status;
+
+-- Test 5: Disable CDC
+SET citus.enable_change_data_capture = false;
+
+-- Test 6: Test with custom library path
+SET dynamic_library_path = '$libdir/custom_lib:$libdir';
+SET citus.enable_change_data_capture = true;
+
+-- Verify that custom paths are preserved when CDC is enabled
+SHOW dynamic_library_path;
+
+-- Test 7: Reset to defaults
+RESET citus.enable_change_data_capture;
+RESET dynamic_library_path;
+
+-- Final verification
+SHOW citus.enable_change_data_capture;
+SHOW dynamic_library_path;
+
+-- Test edge cases
+-- Test 8: Test with empty library path
+SET dynamic_library_path = '';
+SET citus.enable_change_data_capture = true;
+SHOW dynamic_library_path;
+
+-- Test 9: Test with non-standard library path
+SET dynamic_library_path = '/custom/path';
+SET citus.enable_change_data_capture = true;
+SHOW dynamic_library_path;
+
+-- Clean up
+RESET citus.enable_change_data_capture;
+RESET dynamic_library_path;