MDEV-14756 - Remove trx_sys_t::rw_trx_list

Replaced UT_LIST_GET_LEN(trx_sys->rw_trx_list) with
trx_sys->rw_trx_hash.size().
Moved freeing of trx objects at shutdown to rw_trx_hash destructor.
Small clean-up in trx_rollback_recovered().

storage/innobase/include/trx0sys.h

@@ -244,13 +244,6 @@ trx_sys_close(void);
 @return	whether the creation succeeded */
 bool
 trx_sys_create_rsegs();
-/*****************************************************************//**
-Get the number of transaction in the system, independent of their state.
-@return count of transactions in trx_sys_t::trx_list */
-UNIV_INLINE
-ulint
-trx_sys_get_n_rw_trx(void);
-/*======================*/
 
 /*********************************************************************
 Check if there are any active (non-prepared) transactions.
@@ -506,6 +499,35 @@ class rw_trx_hash_t
   }
 
 
+  /**
+    Destructor callback for lock-free allocator.
+
+    This destructor is used at shutdown. It frees remaining transaction
+    objects.
+
+    XA PREPARED transactions may remain if they haven't been committed or
+    rolled back. ACTIVE transactions may remain if startup was interrupted or
+    server is running in read-only mode or for certain srv_force_recovery
+    levels.
+  */
+
+  static void rw_trx_hash_shutdown_destructor(uchar *arg)
+  {
+    rw_trx_hash_element_t *element=
+      reinterpret_cast<rw_trx_hash_element_t*>(arg + LF_HASH_OVERHEAD);
+    if (trx_t *trx= element->trx)
+    {
+      ut_ad(trx_state_eq(trx, TRX_STATE_PREPARED) ||
+            (trx_state_eq(trx, TRX_STATE_ACTIVE) &&
+             (!srv_was_started ||
+              srv_read_only_mode ||
+              srv_force_recovery >= SRV_FORCE_NO_TRX_UNDO)));
+      trx_free_prepared(trx);
+    }
+    element->~rw_trx_hash_element_t();
+  }
+
+
   /**
     Initializer callback for lock-free hash.
 
@@ -522,6 +544,7 @@ class rw_trx_hash_t
                                       rw_trx_hash_element_t *element,
                                       trx_t *trx)
   {
+    ut_ad(element->trx == 0);
     element->trx= trx;
     element->id= trx->id;
     trx->rw_trx_hash_element= element;
@@ -562,6 +585,7 @@ class rw_trx_hash_t
 
   void destroy()
   {
+    hash.alloc.destructor= rw_trx_hash_shutdown_destructor;
     lf_hash_destroy(&hash);
   }
 

storage/innobase/include/trx0sys.ic

@@ -293,22 +293,3 @@ trx_sys_get_max_trx_id(void)
 	return(trx_sys->max_trx_id);
 #endif /* UNIV_WORD_SIZE < DATA_TRX_ID_LEN */
 }
-
-/*****************************************************************//**
-Get the number of transaction in the system, independent of their state.
-@return count of transactions in trx_sys_t::rw_trx_list */
-UNIV_INLINE
-ulint
-trx_sys_get_n_rw_trx(void)
-/*======================*/
-{
-	ulint	n_trx;
-
-	trx_sys_mutex_enter();
-
-	n_trx = UT_LIST_GET_LEN(trx_sys->rw_trx_list);
-
-	trx_sys_mutex_exit();
-
-	return(n_trx);
-}

storage/innobase/trx/trx0roll.cc

@@ -852,16 +852,6 @@ trx_rollback_recovered(bool all)
 
 	ut_a(srv_force_recovery < SRV_FORCE_NO_TRX_UNDO);
 
-	if (trx_sys_get_n_rw_trx() == 0) {
-
-		return;
-	}
-
-	if (all) {
-		ib::info() << "Starting in background the rollback"
-			" of recovered transactions";
-	}
-
 	/* Note: For XA recovered transactions, we rely on MySQL to
 	do rollback. They will be in TRX_STATE_PREPARED state. If the server
 	is shutdown and they are still lingering in trx_sys_t::trx_list
@@ -894,11 +884,6 @@ trx_rollback_recovered(bool all)
 		trx_sys_mutex_exit();
 
 	} while (trx != NULL);
-
-	if (all) {
-		ib::info() << "Rollback of non-prepared transactions"
-			" completed";
-	}
 }
 
 /*******************************************************************//**
@@ -919,7 +904,13 @@ DECLARE_THREAD(trx_rollback_all_recovered)(void*)
 	pfs_register_thread(trx_rollback_clean_thread_key);
 #endif /* UNIV_PFS_THREAD */
 
-	trx_rollback_recovered(true);
+	if (trx_sys->rw_trx_hash.size()) {
+		ib::info() << "Starting in background the rollback of"
+			" recovered transactions";
+		trx_rollback_recovered(true);
+		ib::info() << "Rollback of non-prepared transactions"
+			" completed";
+	}
 
 	trx_rollback_is_active = false;
 

storage/innobase/trx/trx0sys.cc

@@ -591,20 +591,7 @@ trx_sys_close(void)
 		trx_dummy_sess = NULL;
 	}
 
-	/* Only prepared transactions may be left in the system. Free them. */
-	ut_a(UT_LIST_GET_LEN(trx_sys->rw_trx_list) == trx_sys->n_prepared_trx
-	     || !srv_was_started
-	     || srv_read_only_mode
-	     || srv_force_recovery >= SRV_FORCE_NO_TRX_UNDO);
-
-	for (trx_t* trx = UT_LIST_GET_FIRST(trx_sys->rw_trx_list);
-	     trx != NULL;
-	     trx = UT_LIST_GET_FIRST(trx_sys->rw_trx_list)) {
-
-		trx_free_prepared(trx);
-
-		UT_LIST_REMOVE(trx_sys->rw_trx_list, trx);
-	}
+	trx_sys->rw_trx_hash.destroy();
 
 	/* There can't be any active transactions. */
 
@@ -629,7 +616,6 @@ trx_sys_close(void)
 
 	trx_sys->rw_trx_ids.~trx_ids_t();
 
-	trx_sys->rw_trx_hash.destroy();
 	ut_free(trx_sys);
 
 	trx_sys = NULL;
@@ -643,12 +629,9 @@ ulint
 trx_sys_any_active_transactions(void)
 /*=================================*/
 {
-	ulint	total_trx = 0;
+	ulint	total_trx = trx_sys->rw_trx_hash.size();
 
 	trx_sys_mutex_enter();
-
-	total_trx = UT_LIST_GET_LEN(trx_sys->rw_trx_list);
-
 	for (trx_t* trx = UT_LIST_GET_FIRST(trx_sys->mysql_trx_list);
 	     trx != NULL;
 	     trx = UT_LIST_GET_NEXT(mysql_trx_list, trx)) {

storage/innobase/trx/trx0trx.cc

@@ -645,6 +645,7 @@ trx_free_prepared(
 	trx_undo_free_prepared(trx);
 
 	assert_trx_in_rw_list(trx);
+	UT_LIST_REMOVE(trx_sys->rw_trx_list, trx);
 
 	ut_a(!trx->read_only);