Introducing new backend type and disabling caching for daemon backends

src/backend/distributed/connection/connection_management.c

@@ -502,6 +502,12 @@ FindAvailableConnection(dlist_head *connections, uint32 flags)
 			continue;
 		}
 
+        if ((flags & REQUIRE_MAINTENANCE_CONNECTION) &&
+            !connection->useForMaintenanceOperations)
+        {
+            continue;
+        }
+
 		if ((flags & REQUIRE_METADATA_CONNECTION) &&
 			!connection->useForMetadataOperations)
 		{
@@ -1498,7 +1504,7 @@ ShouldShutdownConnection(MultiConnection *connection, const int cachedConnection
 	 * escalating the number of cached connections. We can recognize such backends
 	 * from their application name.
 	 */
-	return (IsCitusInternalBackend() || IsRebalancerInternalBackend()) ||
+    return (isCitusMaintenanceDaemonBackend() || IsCitusInternalBackend() || IsRebalancerInternalBackend()) ||
 		   connection->initializationState != POOL_STATE_INITIALIZED ||
 		   cachedConnectionCount >= MaxCachedConnectionsPerWorker ||
 		   connection->forceCloseAtTransactionEnd ||
@@ -1506,9 +1512,8 @@ ShouldShutdownConnection(MultiConnection *connection, const int cachedConnection
 		   !RemoteTransactionIdle(connection) ||
 		   connection->requiresReplication ||
 		   connection->isReplicationOriginSessionSetup ||
-		   (MaxCachedConnectionLifetime >= 0 &&
+           (MaxCachedConnectionLifetime >= 0
-			MillisecondsToTimeout(connection->connectionEstablishmentStart,
+            && MillisecondsToTimeout(connection->connectionEstablishmentStart, MaxCachedConnectionLifetime) <= 0);
-								  MaxCachedConnectionLifetime) <= 0);
 }
 
 

src/backend/distributed/transaction/backend_data.c

@@ -86,6 +86,7 @@ typedef struct BackendManagementShmemData
 typedef enum CitusBackendType
 {
 	CITUS_BACKEND_NOT_ASSIGNED,
+    CITUS_MAINTENANCE_DAEMON_BACKEND,
 	CITUS_INTERNAL_BACKEND,
 	CITUS_REBALANCER_BACKEND,
 	CITUS_RUN_COMMAND_BACKEND,
@@ -96,6 +97,7 @@ static const char *CitusBackendPrefixes[] = {
 	CITUS_APPLICATION_NAME_PREFIX,
 	CITUS_REBALANCER_APPLICATION_NAME_PREFIX,
 	CITUS_RUN_COMMAND_APPLICATION_NAME_PREFIX,
+    CITUS_MAINTENANCE_DAEMON_APPLICATION_NAME_PREFIX,
 };
 
 static const CitusBackendType CitusBackendTypes[] = {
@@ -1071,7 +1073,6 @@ citus_pid_for_gpid(PG_FUNCTION_ARGS)
 	PG_RETURN_INT32(ExtractProcessIdFromGlobalPID(globalPID));
 }
 
-
 /*
  * ExtractGlobalPID extracts the global process id from the application name and returns it
  * if the application name is not compatible with Citus' application names returns 0.
@@ -1445,6 +1446,17 @@ IsCitusShardTransferBackend(void)
 				   prefixLength) == 0;
 }
 
+bool isCitusMaintenanceDaemonBackend(void)
+{
+    if (CurrentBackendType == CITUS_BACKEND_NOT_ASSIGNED)
+    {
+        DetermineCitusBackendType(application_name);
+    }
+
+    return CurrentBackendType == CITUS_MAINTENANCE_DAEMON_BACKEND;
+}
+
+
 
 /*
  * DetermineCitusBackendType determines the type of backend based on the application_name.

src/backend/distributed/utils/maintenanced.c

@@ -60,6 +60,7 @@
 #include "distributed/statistics_collection.h"
 #include "distributed/transaction_recovery.h"
 #include "distributed/version_compat.h"
+#include "distributed/connection_management.h"
 
 /*
  * Shared memory data for all maintenance workers.
@@ -506,7 +507,7 @@ CitusMaintenanceDaemonMain(Datum main_arg)
 	MaintenanceDaemonDBData *myDbData = ConnectToDatabase(databaseOid);
 
 	/* make worker recognizable in pg_stat_activity */
-	pgstat_report_appname("Citus Maintenance Daemon");
+	pgstat_report_appname(CITUS_MAINTENANCE_DAEMON_APPLICATION_NAME_PREFIX);
 
 	/*
 	 * Terminate orphaned metadata sync daemons spawned from previously terminated

src/include/distributed/backend_data.h

@@ -78,6 +78,7 @@ extern bool IsRebalancerInternalBackend(void);
 extern bool IsCitusRunCommandBackend(void);
 extern bool IsExternalClientBackend(void);
 extern bool IsCitusShardTransferBackend(void);
+extern bool isCitusMaintenanceDaemonBackend(void);
 
 #define INVALID_CITUS_INTERNAL_BACKEND_GPID 0
 #define GLOBAL_PID_NODE_ID_FOR_NODES_NOT_IN_METADATA 99999999

src/include/distributed/connection_management.h

@@ -44,6 +44,8 @@
 /* application name used for connections made by run_command_on_* */
 #define CITUS_RUN_COMMAND_APPLICATION_NAME_PREFIX "citus_run_command gpid="
 
+#define CITUS_MAINTENANCE_DAEMON_APPLICATION_NAME_PREFIX "Citus Maintenance Daemon"
+
 /*
  * application name prefix for move/split replication connections.
  *