MDEV-15326 preparation: Remove trx_sys_t::n_prepared_trx

This is a backport of 900b0790
from MariaDB Server 10.3.

storage/innobase/include/trx0sys.h

@@ -635,18 +635,6 @@ struct trx_sys_t {
 
 	TrxIdSet	rw_trx_set;	/*!< Mapping from transaction id
 					to transaction instance */
-
-	ulint		n_prepared_trx;	/*!< Number of transactions currently
-					in the XA PREPARED state */
-
-	ulint		n_prepared_recovered_trx; /*!< Number of transactions
-					currently in XA PREPARED state that are
-					also recovered. Such transactions cannot
-					be added during runtime. They can only
-					occur after recovery if mysqld crashed
-					while there were XA PREPARED
-					transactions. We disable query cache
-					if such transactions exist. */
 };
 
 /** When a trx id which is zero modulo this number (which must be a power of

storage/innobase/lock/lock0lock.cc

@@ -6552,26 +6552,12 @@ lock_trx_release_locks(
 {
 	check_trx_state(trx);
 
-	if (trx_state_eq(trx, TRX_STATE_PREPARED)
-	    || trx_state_eq(trx, TRX_STATE_PREPARED_RECOVERED)) {
-
-		mutex_enter(&trx_sys->mutex);
-
-		ut_a(trx_sys->n_prepared_trx > 0);
-		--trx_sys->n_prepared_trx;
-
-		if (trx->is_recovered) {
-			ut_a(trx_sys->n_prepared_recovered_trx > 0);
-			trx_sys->n_prepared_recovered_trx--;
-		}
-
-		mutex_exit(&trx_sys->mutex);
-	} else {
-		ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE)
-		      || (trx_state_eq(trx, TRX_STATE_COMMITTED_IN_MEMORY)
-			  && trx->is_recovered
-			  && !UT_LIST_GET_LEN(trx->lock.trx_locks)));
-	}
+	ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE)
+	      || trx_state_eq(trx, TRX_STATE_PREPARED)
+	      || trx_state_eq(trx, TRX_STATE_PREPARED_RECOVERED)
+	      || (trx_state_eq(trx, TRX_STATE_COMMITTED_IN_MEMORY)
+		  && trx->is_recovered
+		  && !UT_LIST_GET_LEN(trx->lock.trx_locks)));
 
 	bool	release_lock;
 

storage/innobase/trx/trx0roll.cc

@@ -722,8 +722,6 @@ trx_rollback_resurrected(
 		    && !srv_undo_sources && srv_fast_shutdown) {
 fake_prepared:
 			trx->state = TRX_STATE_PREPARED;
-			trx_sys->n_prepared_trx++;
-			trx_sys->n_prepared_recovered_trx++;
 			*all = FALSE;
 			goto func_exit;
 		}

storage/innobase/trx/trx0sys.cc

@@ -924,13 +924,7 @@ trx_sys_close(void)
 	}
 
 	/* 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);
-
 	while (trx_t* trx = UT_LIST_GET_FIRST(trx_sys->rw_trx_list)) {
-		UT_LIST_REMOVE(trx_sys->rw_trx_list, trx);
 		trx_free_prepared(trx);
 	}
 
@@ -976,17 +970,41 @@ trx_sys_any_active_transactions(void)
 
 	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->rw_trx_list);
+	     trx != NULL;
+	     trx = UT_LIST_GET_NEXT(trx_list, trx)) {
+		ut_ad(trx->in_rw_trx_list);
+		trx_mutex_enter(trx);
+		switch (trx->state) {
+		case TRX_STATE_NOT_STARTED:
+			DBUG_ASSERT(!"invalid state");
+			/* fall through */
+		case TRX_STATE_PREPARED:
+		case TRX_STATE_PREPARED_RECOVERED:
+			break;
+		case TRX_STATE_ACTIVE:
+		case TRX_STATE_COMMITTED_IN_MEMORY:
+			total_trx++;
+		}
+		trx_mutex_exit(trx);
+	}
 
 	for (trx_t* trx = UT_LIST_GET_FIRST(trx_sys->mysql_trx_list);
 	     trx != NULL;
 	     trx = UT_LIST_GET_NEXT(mysql_trx_list, trx)) {
-		total_trx += trx->state != TRX_STATE_NOT_STARTED;
+		ut_ad(trx->in_mysql_trx_list);
+		trx_mutex_enter(trx);
+		/* This may count some ACTIVE transactions twice,
+		both in rw_trx_list and mysql_trx_list. */
+		total_trx += trx->state == TRX_STATE_ACTIVE;
+		/* Any PREPARED or COMMITTED transactions must be
+		in rw_trx_list, so it suffices to count them there. */
+		ut_ad(trx->in_rw_trx_list
+		      || trx->state == TRX_STATE_NOT_STARTED
+		      || trx->state == TRX_STATE_ACTIVE);
+		trx_mutex_exit(trx);
 	}
 
-	ut_a(total_trx >= trx_sys->n_prepared_trx);
-	total_trx -= trx_sys->n_prepared_trx;
-
 	trx_sys_mutex_exit();
 
 	return(total_trx);

storage/innobase/trx/trx0trx.cc

@@ -526,6 +526,11 @@ trx_free_prepared(
 /*==============*/
 	trx_t*	trx)	/*!< in, own: trx object */
 {
+	ut_ad(trx->state == TRX_STATE_PREPARED
+	      || trx->state == TRX_STATE_PREPARED_RECOVERED
+	      || !srv_was_started
+	      || srv_read_only_mode
+	      || srv_force_recovery >= SRV_FORCE_NO_TRX_UNDO);
 	ut_a(trx_state_eq(trx, TRX_STATE_PREPARED)
 	     || trx_state_eq(trx, TRX_STATE_PREPARED_RECOVERED)
 	     || (trx->is_recovered
@@ -545,7 +550,9 @@ trx_free_prepared(
 
 	ut_a(!trx->read_only);
 
-	ut_d(trx->in_rw_trx_list = FALSE);
+	ut_ad(trx->in_rw_trx_list);
+	UT_LIST_REMOVE(trx_sys->rw_trx_list, trx);
+	ut_d(trx->in_rw_trx_list = false);
 
 	DBUG_LOG("trx", "Free prepared: " << trx);
 	trx->state = TRX_STATE_NOT_STARTED;
@@ -594,7 +601,6 @@ trx_disconnect_from_mysql(
 		ut_ad(trx_state_eq(trx, TRX_STATE_PREPARED));
 
 		trx->is_recovered = true;
-		trx_sys->n_prepared_recovered_trx++;
 	        trx->mysql_thd = NULL;
 		/* todo/fixme: suggest to do it at innodb prepare */
 		trx->will_lock = 0;
@@ -756,8 +762,6 @@ trx_resurrect_insert(
 				<< " was in the XA prepared state.";
 
 			trx->state = TRX_STATE_PREPARED;
-			trx_sys->n_prepared_trx++;
-			trx_sys->n_prepared_recovered_trx++;
 		} else {
 			trx->state = TRX_STATE_COMMITTED_IN_MEMORY;
 		}
@@ -815,13 +819,8 @@ trx_resurrect_update_in_prepared_state(
 	if (undo->state == TRX_UNDO_PREPARED) {
 		ib::info() << "Transaction " << trx_get_id_for_print(trx)
 			<< " was in the XA prepared state.";
-
-		if (trx_state_eq(trx, TRX_STATE_NOT_STARTED)) {
-			trx_sys->n_prepared_trx++;
-			trx_sys->n_prepared_recovered_trx++;
-		} else {
-			ut_ad(trx_state_eq(trx, TRX_STATE_PREPARED));
-		}
+		ut_ad(trx_state_eq(trx, TRX_STATE_NOT_STARTED)
+		      || trx_state_eq(trx, TRX_STATE_PREPARED));
 
 		trx->state = TRX_STATE_PREPARED;
 	} else {
@@ -2609,10 +2608,9 @@ trx_prepare(
 
 	/*--------------------------------------*/
 	ut_a(trx->state == TRX_STATE_ACTIVE);
-	trx_sys_mutex_enter();
+	trx_mutex_enter(trx);
 	trx->state = TRX_STATE_PREPARED;
-	trx_sys->n_prepared_trx++;
-	trx_sys_mutex_exit();
+	trx_mutex_exit(trx);
 	/*--------------------------------------*/
 
 	if (lsn) {