[Tarantool-patches] [PATCH v3 07/12] box: introduce `box.ctl.demote`

[Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Introduce a new journal entry, DEMOTE. The entry has the same meaning as
PROMOTE, with the only difference that it clears limbo ownership instead
of transferring it to the issuer.

Introduce `box.ctl.demote`, which works exactly like `box.ctl.promote`,
but results in writing DEMOTE instead of PROMOTE.

A new request was necessary instead of simply writing PROMOTE(origin_id
= 0), because origin_id is deduced from row.replica_id, which cannot be
0 for replicated rows (it's always equal to instance_id of the row
originator).

Closes #6034

@TarantoolBot document
Title: box.ctl.demote

`box.ctl.demote()` is a new function, which works exactly like
`box.ctl.promote()`, with one exception that it results in the instance
writing DEMOTE request to WAL instead of a PROMOTE request.

A DEMOTE request (DEMOTE = 32) copies PROMOTE behaviour (it clears the
limbo as well), but clears the synchronous transaction queue  ownership instead
of assigning it to a new instance.
---
 src/box/box.cc                                |  48 ++++-
 src/box/box.h                                 |   3 +
 src/box/iproto_constants.h                    |  10 +-
 src/box/lua/ctl.c                             |   9 +
 src/box/txn_limbo.c                           |  37 +++-
 src/box/txn_limbo.h                           |   7 +
 test/box/error.result                         |   1 +
 test/replication/election_basic.result        |   3 +
 test/replication/election_basic.test.lua      |   1 +
 test/replication/election_qsync.result        |   3 +
 test/replication/election_qsync.test.lua      |   1 +
 .../gh-5140-qsync-casc-rollback.result        |   6 +
 .../gh-5140-qsync-casc-rollback.test.lua      |   2 +
 .../gh-5144-qsync-dup-confirm.result          |   6 +
 .../gh-5144-qsync-dup-confirm.test.lua        |   2 +
 .../gh-5163-qsync-restart-crash.result        |   6 +
 .../gh-5163-qsync-restart-crash.test.lua      |   2 +
 .../gh-5167-qsync-rollback-snap.result        |   6 +
 .../gh-5167-qsync-rollback-snap.test.lua      |   2 +
 .../gh-5195-qsync-replica-write.result        |  10 +-
 .../gh-5195-qsync-replica-write.test.lua      |   6 +-
 .../gh-5213-qsync-applier-order-3.result      |   9 +
 .../gh-5213-qsync-applier-order-3.test.lua    |   3 +
 .../gh-5213-qsync-applier-order.result        |   6 +
 .../gh-5213-qsync-applier-order.test.lua      |   2 +
 .../replication/gh-5288-qsync-recovery.result |   6 +
 .../gh-5288-qsync-recovery.test.lua           |   2 +
 .../gh-5298-qsync-recovery-snap.result        |   6 +
 .../gh-5298-qsync-recovery-snap.test.lua      |   2 +
 .../gh-5426-election-on-off.result            |   3 +
 .../gh-5426-election-on-off.test.lua          |   1 +
 .../gh-5433-election-restart-recovery.result  |   3 +
 ...gh-5433-election-restart-recovery.test.lua |   1 +
 ...sync-clear-synchro-queue-commit-all.result |   3 +
 ...nc-clear-synchro-queue-commit-all.test.lua |   1 +
 test/replication/gh-5438-raft-state.result    |   3 +
 test/replication/gh-5438-raft-state.test.lua  |   1 +
 .../gh-5446-qsync-eval-quorum.result          |   7 +
 .../gh-5446-qsync-eval-quorum.test.lua        |   3 +
 .../gh-5506-election-on-off.result            |   3 +
 .../gh-5506-election-on-off.test.lua          |   1 +
 .../gh-5566-final-join-synchro.result         |   6 +
 .../gh-5566-final-join-synchro.test.lua       |   2 +
 .../gh-5874-qsync-txn-recovery.result         |   6 +
 .../gh-5874-qsync-txn-recovery.test.lua       |   2 +
 .../gh-6032-promote-wal-write.result          |   3 +
 .../gh-6032-promote-wal-write.test.lua        |   1 +
 .../gh-6034-limbo-ownership.result            | 189 ++++++++++++++++++
 .../gh-6034-limbo-ownership.test.lua          |  69 +++++++
 .../gh-6034-promote-bump-term.result          |   3 +
 .../gh-6034-promote-bump-term.test.lua        |   1 +
 .../gh-6057-qsync-confirm-async-no-wal.result |   7 +
 ...h-6057-qsync-confirm-async-no-wal.test.lua |   3 +
 test/replication/hang_on_synchro_fail.result  |   6 +
 .../replication/hang_on_synchro_fail.test.lua |   2 +
 test/replication/qsync_advanced.result        |  12 ++
 test/replication/qsync_advanced.test.lua      |   4 +
 test/replication/qsync_basic.result           |  33 ++-
 test/replication/qsync_basic.test.lua         |  16 +-
 test/replication/qsync_errinj.result          |   6 +
 test/replication/qsync_errinj.test.lua        |   2 +
 test/replication/qsync_snapshots.result       |   6 +
 test/replication/qsync_snapshots.test.lua     |   2 +
 test/replication/qsync_with_anon.result       |   6 +
 test/replication/qsync_with_anon.test.lua     |   2 +
 test/replication/suite.cfg                    |   1 +
 66 files changed, 579 insertions(+), 48 deletions(-)
 create mode 100644 test/replication/gh-6034-limbo-ownership.result
 create mode 100644 test/replication/gh-6034-limbo-ownership.test.lua

diff --git a/src/box/box.cc b/src/box/box.cc
index 1d894be97..86c5967b9 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -1527,13 +1527,14 @@ box_wait_quorum(uint32_t lead_id, int64_t target_lsn, int quorum,
 	return 0;
 }
 
-int
-box_promote(void)
+static int
+box_clear_synchro_queue(bool demote)
 {
 	/* A guard to block multiple simultaneous function invocations. */
 	static bool in_promote = false;
 	if (in_promote) {
-		diag_set(ClientError, ER_UNSUPPORTED, "box.ctl.promote",
+		diag_set(ClientError, ER_UNSUPPORTED,
+			 demote ? "box.ctl.demote" : "box.ctl.promote",
 			 "simultaneous invocations");
 		return -1;
 	}
@@ -1554,13 +1555,18 @@ box_promote(void)
 		return -1;
 	case ELECTION_MODE_MANUAL:
 	case ELECTION_MODE_CANDIDATE:
-		run_elections = box_raft()->state != RAFT_STATE_LEADER;
+		/*
+		 * No elections involved in a DEMOTE or when the instance is
+		 * already the leader.
+		 */
+		run_elections = box_raft()->state != RAFT_STATE_LEADER &&
+				!demote;
 		/*
 		 * Do nothing when PROMOTE was already written for this term
 		 * (synchronous replication and leader election are in sync, and
 		 * both chose this node as a leader).
 		 */
-		if (txn_limbo_replica_term(&txn_limbo, instance_id) ==
+		if (!demote && txn_limbo_replica_term(&txn_limbo, instance_id) ==
 		    box_raft()->term)
 			return 0;
 
@@ -1674,15 +1680,22 @@ box_promote(void)
 			rc = -1;
 		} else {
 promote:
-			if (try_wait) {
+			if (try_wait || demote) {
 				raft_new_term(box_raft());
 				if (box_raft_wait_persisted() < 0)
 					return -1;
 			}
 			uint64_t term = box_raft()->term;
-			txn_limbo_write_promote(&txn_limbo, wait_lsn, term);
+			if (demote) {
+				txn_limbo_write_demote(&txn_limbo, wait_lsn,
+						       term);
+			} else {
+				txn_limbo_write_promote(&txn_limbo, wait_lsn,
+							term);
+			}
+			uint16_t type = demote ? IPROTO_DEMOTE : IPROTO_PROMOTE;
 			struct synchro_request req = {
-				.type = IPROTO_PROMOTE,
+				.type = type,
 				.replica_id = former_leader_id,
 				.origin_id = instance_id,
 				.lsn = wait_lsn,
@@ -1695,6 +1708,25 @@ promote:
 	return rc;
 }
 
+int
+box_promote(void)
+{
+	return box_clear_synchro_queue(false);
+}
+
+int
+box_demote(void)
+{
+	if (txn_limbo.owner_id == REPLICA_ID_NIL)
+		return 0;
+	if (txn_limbo.owner_id != instance_id) {
+		diag_set(ClientError, ER_SYNC_QUEUE_FOREIGN,
+			 txn_limbo.owner_id);
+		return -1;
+	}
+	return box_clear_synchro_queue(true);
+}
+
 int
 box_listen(void)
 {
diff --git a/src/box/box.h b/src/box/box.h
index ecf32240d..aaf20d9dd 100644
--- a/src/box/box.h
+++ b/src/box/box.h
@@ -276,6 +276,9 @@ typedef struct tuple box_tuple_t;
 int
 box_promote(void);
 
+int
+box_demote(void);
+
 /* box_select is private and used only by FFI */
 API_EXPORT int
 box_select(uint32_t space_id, uint32_t index_id,
diff --git a/src/box/iproto_constants.h b/src/box/iproto_constants.h
index 137bee9da..3c9edb7d2 100644
--- a/src/box/iproto_constants.h
+++ b/src/box/iproto_constants.h
@@ -241,6 +241,8 @@ enum iproto_type {
 	IPROTO_RAFT = 30,
 	/** PROMOTE request. */
 	IPROTO_PROMOTE = 31,
+	/** DEMOTE request. */
+	IPROTO_DEMOTE = 32,
 
 	/** A confirmation message for synchronous transactions. */
 	IPROTO_CONFIRM = 40,
@@ -310,6 +312,8 @@ iproto_type_name(uint16_t type)
 		return "RAFT";
 	case IPROTO_PROMOTE:
 		return "PROMOTE";
+	case IPROTO_DEMOTE:
+		return "DEMOTE";
 	case IPROTO_CONFIRM:
 		return "CONFIRM";
 	case IPROTO_ROLLBACK:
@@ -364,14 +368,14 @@ static inline bool
 iproto_type_is_synchro_request(uint16_t type)
 {
 	return type == IPROTO_CONFIRM || type == IPROTO_ROLLBACK ||
-	       type == IPROTO_PROMOTE;
+	       type == IPROTO_PROMOTE || type == IPROTO_DEMOTE;
 }
 
-/** PROMOTE entry (synchronous replication and leader elections). */
+/** PROMOTE/DEMOTE entry (synchronous replication and leader elections). */
 static inline bool
 iproto_type_is_promote_request(uint32_t type)
 {
-       return type == IPROTO_PROMOTE;
+       return type == IPROTO_PROMOTE || type == IPROTO_DEMOTE;
 }
 
 static inline bool
diff --git a/src/box/lua/ctl.c b/src/box/lua/ctl.c
index 368b9ab60..a613c4111 100644
--- a/src/box/lua/ctl.c
+++ b/src/box/lua/ctl.c
@@ -89,6 +89,14 @@ lbox_ctl_promote(struct lua_State *L)
 	return 0;
 }
 
+static int
+lbox_ctl_demote(struct lua_State *L)
+{
+	if (box_demote() != 0)
+		return luaT_error(L);
+	return 0;
+}
+
 static int
 lbox_ctl_is_recovery_finished(struct lua_State *L)
 {
@@ -127,6 +135,7 @@ static const struct luaL_Reg lbox_ctl_lib[] = {
 	{"promote", lbox_ctl_promote},
 	/* An old alias. */
 	{"clear_synchro_queue", lbox_ctl_promote},
+	{"demote", lbox_ctl_demote},
 	{"is_recovery_finished", lbox_ctl_is_recovery_finished},
 	{"set_on_shutdown_timeout", lbox_ctl_set_on_shutdown_timeout},
 	{NULL, NULL}
diff --git a/src/box/txn_limbo.c b/src/box/txn_limbo.c
index 996f1a3fc..d21f05557 100644
--- a/src/box/txn_limbo.c
+++ b/src/box/txn_limbo.c
@@ -508,6 +508,29 @@ txn_limbo_read_promote(struct txn_limbo *limbo, uint32_t replica_id,
 	limbo->confirmed_lsn = 0;
 }
 
+void
+txn_limbo_write_demote(struct txn_limbo *limbo, int64_t lsn, uint64_t term)
+{
+	limbo->confirmed_lsn = lsn;
+	limbo->is_in_rollback = true;
+	struct txn_limbo_entry *e = txn_limbo_last_synchro_entry(limbo);
+	assert(e == NULL || e->lsn <= lsn);
+	(void)e;
+	txn_limbo_write_synchro(limbo, IPROTO_DEMOTE, lsn, term);
+	limbo->is_in_rollback = false;
+}
+
+/**
+ * Process a DEMOTE request, which's like PROMOTE, but clears the limbo
+ * ownership.
+ * @sa txn_limbo_read_promote.
+ */
+static void
+txn_limbo_read_demote(struct txn_limbo *limbo, int64_t lsn)
+{
+	return txn_limbo_read_promote(limbo, REPLICA_ID_NIL, lsn);
+}
+
 void
 txn_limbo_ack(struct txn_limbo *limbo, uint32_t replica_id, int64_t lsn)
 {
@@ -659,12 +682,13 @@ txn_limbo_process(struct txn_limbo *limbo, const struct synchro_request *req)
 		vclock_follow(&limbo->promote_term_map, origin, term);
 		if (term > limbo->promote_greatest_term)
 			limbo->promote_greatest_term = term;
-	} else if (req->type == IPROTO_PROMOTE &&
+	} else if (iproto_type_is_promote_request(req->type) &&
 		   limbo->promote_greatest_term > 1) {
 		/* PROMOTE for outdated term. Ignore. */
-		say_info("RAFT: ignoring PROMOTE request from instance "
+		say_info("RAFT: ignoring %s request from instance "
 			 "id %u for term %llu. Greatest term seen "
-			 "before (%llu) is bigger.", origin, (long long)term,
+			 "before (%llu) is bigger.",
+			 iproto_type_name(req->type), origin, (long long)term,
 			 (long long)limbo->promote_greatest_term);
 		return;
 	}
@@ -675,7 +699,7 @@ txn_limbo_process(struct txn_limbo *limbo, const struct synchro_request *req)
 		 * The limbo was empty on the instance issuing the request.
 		 * This means this instance must empty its limbo as well.
 		 */
-		assert(lsn == 0 && req->type == IPROTO_PROMOTE);
+		assert(lsn == 0 && iproto_type_is_promote_request(req->type));
 	} else if (req->replica_id != limbo->owner_id) {
 		/*
 		 * Ignore CONFIRM/ROLLBACK messages for a foreign master.
@@ -683,7 +707,7 @@ txn_limbo_process(struct txn_limbo *limbo, const struct synchro_request *req)
 		 * data from an old leader, who has just started and written
 		 * confirm right on synchronous transaction recovery.
 		 */
-		if (req->type != IPROTO_PROMOTE)
+		if (!iproto_type_is_promote_request(req->type))
 			return;
 		/*
 		 * Promote has a bigger term, and tries to steal the limbo. It
@@ -703,6 +727,9 @@ txn_limbo_process(struct txn_limbo *limbo, const struct synchro_request *req)
 	case IPROTO_PROMOTE:
 		txn_limbo_read_promote(limbo, req->origin_id, lsn);
 		break;
+	case IPROTO_DEMOTE:
+		txn_limbo_read_demote(limbo, lsn);
+		break;
 	default:
 		unreachable();
 	}
diff --git a/src/box/txn_limbo.h b/src/box/txn_limbo.h
index e409ac657..801a1a0ee 100644
--- a/src/box/txn_limbo.h
+++ b/src/box/txn_limbo.h
@@ -318,6 +318,13 @@ txn_limbo_wait_confirm(struct txn_limbo *limbo);
 void
 txn_limbo_write_promote(struct txn_limbo *limbo, int64_t lsn, uint64_t term);
 
+/**
+ * Write a DEMOTE request.
+ * It has the same effect as PROMOTE and additionally clears limbo ownership.
+ */
+void
+txn_limbo_write_demote(struct txn_limbo *limbo, int64_t lsn, uint64_t term);
+
 /**
  * Update qsync parameters dynamically.
  */
diff --git a/test/box/error.result b/test/box/error.result
index dfe593dc2..8f783f927 100644
--- a/test/box/error.result
+++ b/test/box/error.result
@@ -445,6 +445,7 @@ t;
  |   224: box.error.RAFT_DISABLED
  |   225: box.error.TXN_ROLLBACK
  |   226: box.error.SYNC_QUEUE_UNCLAIMED
+ |   227: box.error.SYNC_QUEUE_FOREIGN
  | ...
 
 test_run:cmd("setopt delimiter ''");
diff --git a/test/replication/election_basic.result b/test/replication/election_basic.result
index b64028c60..c0323a042 100644
--- a/test/replication/election_basic.result
+++ b/test/replication/election_basic.result
@@ -114,6 +114,9 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
 
 --
 -- See if bootstrap with election enabled works.
diff --git a/test/replication/election_basic.test.lua b/test/replication/election_basic.test.lua
index 77fdf6340..085a499d5 100644
--- a/test/replication/election_basic.test.lua
+++ b/test/replication/election_basic.test.lua
@@ -43,6 +43,7 @@ box.cfg{
     election_mode = 'off',                                                      \
     election_timeout = old_election_timeout                                     \
 }
+box.ctl.demote()
 
 --
 -- See if bootstrap with election enabled works.
diff --git a/test/replication/election_qsync.result b/test/replication/election_qsync.result
index c06400b38..2402c8578 100644
--- a/test/replication/election_qsync.result
+++ b/test/replication/election_qsync.result
@@ -165,6 +165,9 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
 box.schema.user.revoke('guest', 'super')
  | ---
  | ...
diff --git a/test/replication/election_qsync.test.lua b/test/replication/election_qsync.test.lua
index ea6fc4a61..e1aca8351 100644
--- a/test/replication/election_qsync.test.lua
+++ b/test/replication/election_qsync.test.lua
@@ -84,4 +84,5 @@ box.cfg{
     replication = old_replication,                                              \
     replication_synchro_timeout = old_replication_synchro_timeout,              \
 }
+box.ctl.demote()
 box.schema.user.revoke('guest', 'super')
diff --git a/test/replication/gh-5140-qsync-casc-rollback.result b/test/replication/gh-5140-qsync-casc-rollback.result
index da77631dd..d3208e1a4 100644
--- a/test/replication/gh-5140-qsync-casc-rollback.result
+++ b/test/replication/gh-5140-qsync-casc-rollback.result
@@ -73,6 +73,9 @@ _ = box.schema.space.create('async', {is_sync=false, engine = engine})
 _ = _:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 -- Write something to flush the master state to replica.
 box.space.sync:replace{1}
  | ---
@@ -222,3 +225,6 @@ test_run:cmd('delete server replica')
 box.schema.user.revoke('guest', 'super')
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-5140-qsync-casc-rollback.test.lua b/test/replication/gh-5140-qsync-casc-rollback.test.lua
index 69fc9ad02..96ddfd260 100644
--- a/test/replication/gh-5140-qsync-casc-rollback.test.lua
+++ b/test/replication/gh-5140-qsync-casc-rollback.test.lua
@@ -48,6 +48,7 @@ _ = box.schema.space.create('sync', {is_sync = true, engine = engine})
 _ = _:create_index('pk')
 _ = box.schema.space.create('async', {is_sync=false, engine = engine})
 _ = _:create_index('pk')
+box.ctl.promote()
 -- Write something to flush the master state to replica.
 box.space.sync:replace{1}
 
@@ -103,3 +104,4 @@ test_run:cmd('stop server replica')
 test_run:cmd('delete server replica')
 
 box.schema.user.revoke('guest', 'super')
+box.ctl.demote()
diff --git a/test/replication/gh-5144-qsync-dup-confirm.result b/test/replication/gh-5144-qsync-dup-confirm.result
index 9d265d9ff..217e44412 100644
--- a/test/replication/gh-5144-qsync-dup-confirm.result
+++ b/test/replication/gh-5144-qsync-dup-confirm.result
@@ -46,6 +46,9 @@ _ = box.schema.space.create('sync', {is_sync = true, engine = engine})
 _ = _:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 
 -- Remember the current LSN. In the end, when the following synchronous
 -- transaction is committed, result LSN should be this value +2: for the
@@ -148,6 +151,9 @@ test_run:cmd('delete server replica2')
  | - true
  | ...
 
+box.ctl.demote()
+ | ---
+ | ...
 box.schema.user.revoke('guest', 'super')
  | ---
  | ...
diff --git a/test/replication/gh-5144-qsync-dup-confirm.test.lua b/test/replication/gh-5144-qsync-dup-confirm.test.lua
index 01a8351e0..1d6af2c62 100644
--- a/test/replication/gh-5144-qsync-dup-confirm.test.lua
+++ b/test/replication/gh-5144-qsync-dup-confirm.test.lua
@@ -19,6 +19,7 @@ box.cfg{replication_synchro_quorum = 2, replication_synchro_timeout = 1000}
 
 _ = box.schema.space.create('sync', {is_sync = true, engine = engine})
 _ = _:create_index('pk')
+box.ctl.promote()
 
 -- Remember the current LSN. In the end, when the following synchronous
 -- transaction is committed, result LSN should be this value +2: for the
@@ -69,4 +70,5 @@ test_run:cmd('delete server replica1')
 test_run:cmd('stop server replica2')
 test_run:cmd('delete server replica2')
 
+box.ctl.demote()
 box.schema.user.revoke('guest', 'super')
diff --git a/test/replication/gh-5163-qsync-restart-crash.result b/test/replication/gh-5163-qsync-restart-crash.result
index e57bc76d1..1b4d3d9b5 100644
--- a/test/replication/gh-5163-qsync-restart-crash.result
+++ b/test/replication/gh-5163-qsync-restart-crash.result
@@ -16,6 +16,9 @@ _ = box.schema.space.create('sync', {is_sync=true, engine=engine})
 _ = box.space.sync:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 
 box.space.sync:replace{1}
  | ---
@@ -30,3 +33,6 @@ box.space.sync:select{}
 box.space.sync:drop()
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-5163-qsync-restart-crash.test.lua b/test/replication/gh-5163-qsync-restart-crash.test.lua
index d5aca4749..c8d54aad2 100644
--- a/test/replication/gh-5163-qsync-restart-crash.test.lua
+++ b/test/replication/gh-5163-qsync-restart-crash.test.lua
@@ -7,8 +7,10 @@ engine = test_run:get_cfg('engine')
 --
 _ = box.schema.space.create('sync', {is_sync=true, engine=engine})
 _ = box.space.sync:create_index('pk')
+box.ctl.promote()
 
 box.space.sync:replace{1}
 test_run:cmd('restart server default')
 box.space.sync:select{}
 box.space.sync:drop()
+box.ctl.demote()
diff --git a/test/replication/gh-5167-qsync-rollback-snap.result b/test/replication/gh-5167-qsync-rollback-snap.result
index 06f58526c..13166720f 100644
--- a/test/replication/gh-5167-qsync-rollback-snap.result
+++ b/test/replication/gh-5167-qsync-rollback-snap.result
@@ -41,6 +41,9 @@ _ = box.schema.space.create('sync', {is_sync = true, engine = engine})
 _ = box.space.sync:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 -- Write something to flush the current master's state to replica.
 _ = box.space.sync:insert{1}
  | ---
@@ -163,3 +166,6 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-5167-qsync-rollback-snap.test.lua b/test/replication/gh-5167-qsync-rollback-snap.test.lua
index 475727e61..1a2a31b7c 100644
--- a/test/replication/gh-5167-qsync-rollback-snap.test.lua
+++ b/test/replication/gh-5167-qsync-rollback-snap.test.lua
@@ -16,6 +16,7 @@ fiber = require('fiber')
 box.cfg{replication_synchro_quorum = 2, replication_synchro_timeout = 1000}
 _ = box.schema.space.create('sync', {is_sync = true, engine = engine})
 _ = box.space.sync:create_index('pk')
+box.ctl.promote()
 -- Write something to flush the current master's state to replica.
 _ = box.space.sync:insert{1}
 _ = box.space.sync:delete{1}
@@ -65,3 +66,4 @@ box.cfg{
     replication_synchro_quorum = orig_synchro_quorum,                           \
     replication_synchro_timeout = orig_synchro_timeout,                         \
 }
+box.ctl.demote()
diff --git a/test/replication/gh-5195-qsync-replica-write.result b/test/replication/gh-5195-qsync-replica-write.result
index 85e00e6ed..bc73bb599 100644
--- a/test/replication/gh-5195-qsync-replica-write.result
+++ b/test/replication/gh-5195-qsync-replica-write.result
@@ -40,6 +40,9 @@ _ = box.schema.space.create('sync', {engine = engine, is_sync = true})
 _ = box.space.sync:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 
 box.cfg{replication_synchro_timeout = 1000, replication_synchro_quorum = 3}
  | ---
@@ -71,12 +74,12 @@ test_run:wait_lsn('replica', 'default')
  | ---
  | ...
 -- Normal DML is blocked - the limbo is not empty and does not belong to the
--- replica. But synchro queue cleanup also does a WAL write, and propagates LSN
+-- replica. But promote also does a WAL write, and propagates LSN
 -- of the instance.
 box.cfg{replication_synchro_timeout = 0.001}
  | ---
  | ...
-box.ctl.clear_synchro_queue()
+box.ctl.promote()
  | ---
  | ...
 
@@ -144,6 +147,9 @@ test_run:cmd('delete server replica')
  | - true
  | ...
 
+box.ctl.demote()
+ | ---
+ | ...
 box.space.sync:drop()
  | ---
  | ...
diff --git a/test/replication/gh-5195-qsync-replica-write.test.lua b/test/replication/gh-5195-qsync-replica-write.test.lua
index 64c48be99..a59ec154e 100644
--- a/test/replication/gh-5195-qsync-replica-write.test.lua
+++ b/test/replication/gh-5195-qsync-replica-write.test.lua
@@ -17,6 +17,7 @@ test_run:cmd('start server replica with wait=True, wait_load=True')
 --
 _ = box.schema.space.create('sync', {engine = engine, is_sync = true})
 _ = box.space.sync:create_index('pk')
+box.ctl.promote()
 
 box.cfg{replication_synchro_timeout = 1000, replication_synchro_quorum = 3}
 lsn = box.info.lsn
@@ -30,10 +31,10 @@ test_run:wait_cond(function() return box.info.lsn == lsn end)
 test_run:switch('replica')
 test_run:wait_lsn('replica', 'default')
 -- Normal DML is blocked - the limbo is not empty and does not belong to the
--- replica. But synchro queue cleanup also does a WAL write, and propagates LSN
+-- replica. But promote also does a WAL write, and propagates LSN
 -- of the instance.
 box.cfg{replication_synchro_timeout = 0.001}
-box.ctl.clear_synchro_queue()
+box.ctl.promote()
 
 test_run:switch('default')
 -- Wait second ACK receipt.
@@ -59,6 +60,7 @@ test_run:switch('default')
 test_run:cmd('stop server replica')
 test_run:cmd('delete server replica')
 
+box.ctl.demote()
 box.space.sync:drop()
 box.schema.user.revoke('guest', 'super')
 
diff --git a/test/replication/gh-5213-qsync-applier-order-3.result b/test/replication/gh-5213-qsync-applier-order-3.result
index bcb18b5c0..e788eec77 100644
--- a/test/replication/gh-5213-qsync-applier-order-3.result
+++ b/test/replication/gh-5213-qsync-applier-order-3.result
@@ -45,6 +45,9 @@ s = box.schema.space.create('test', {is_sync = true})
 _ = s:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 
 test_run:cmd('create server replica1 with rpl_master=default,\
               script="replication/replica1.lua"')
@@ -179,6 +182,9 @@ box.cfg{
 -- Replica2 takes the limbo ownership and sends the transaction to the replica1.
 -- Along with the CONFIRM from the default node, which is still not applied
 -- on the replica1.
+box.ctl.promote()
+ | ---
+ | ...
 fiber = require('fiber')
  | ---
  | ...
@@ -261,3 +267,6 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-5213-qsync-applier-order-3.test.lua b/test/replication/gh-5213-qsync-applier-order-3.test.lua
index 37b569da7..304656de0 100644
--- a/test/replication/gh-5213-qsync-applier-order-3.test.lua
+++ b/test/replication/gh-5213-qsync-applier-order-3.test.lua
@@ -30,6 +30,7 @@ box.schema.user.grant('guest', 'super')
 
 s = box.schema.space.create('test', {is_sync = true})
 _ = s:create_index('pk')
+box.ctl.promote()
 
 test_run:cmd('create server replica1 with rpl_master=default,\
               script="replication/replica1.lua"')
@@ -90,6 +91,7 @@ box.cfg{
 -- Replica2 takes the limbo ownership and sends the transaction to the replica1.
 -- Along with the CONFIRM from the default node, which is still not applied
 -- on the replica1.
+box.ctl.promote()
 fiber = require('fiber')
 f = fiber.new(function() box.space.test:replace{2} end)
 
@@ -123,3 +125,4 @@ box.cfg{
     replication_synchro_quorum = old_synchro_quorum,                            \
     replication_synchro_timeout = old_synchro_timeout,                          \
 }
+box.ctl.demote()
diff --git a/test/replication/gh-5213-qsync-applier-order.result b/test/replication/gh-5213-qsync-applier-order.result
index a8c24c289..ba6cdab06 100644
--- a/test/replication/gh-5213-qsync-applier-order.result
+++ b/test/replication/gh-5213-qsync-applier-order.result
@@ -29,6 +29,9 @@ s = box.schema.space.create('test', {is_sync = true})
 _ = s:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 
 test_run:cmd('create server replica with rpl_master=default,\
               script="replication/gh-5213-replica.lua"')
@@ -300,3 +303,6 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-5213-qsync-applier-order.test.lua b/test/replication/gh-5213-qsync-applier-order.test.lua
index f1eccfa84..39b1912e8 100644
--- a/test/replication/gh-5213-qsync-applier-order.test.lua
+++ b/test/replication/gh-5213-qsync-applier-order.test.lua
@@ -14,6 +14,7 @@ box.schema.user.grant('guest', 'super')
 
 s = box.schema.space.create('test', {is_sync = true})
 _ = s:create_index('pk')
+box.ctl.promote()
 
 test_run:cmd('create server replica with rpl_master=default,\
               script="replication/gh-5213-replica.lua"')
@@ -120,3 +121,4 @@ box.cfg{
     replication_synchro_quorum = old_synchro_quorum,                            \
     replication_synchro_timeout = old_synchro_timeout,                          \
 }
+box.ctl.demote()
diff --git a/test/replication/gh-5288-qsync-recovery.result b/test/replication/gh-5288-qsync-recovery.result
index dc0babef6..704b71d93 100644
--- a/test/replication/gh-5288-qsync-recovery.result
+++ b/test/replication/gh-5288-qsync-recovery.result
@@ -12,6 +12,9 @@ s = box.schema.space.create('sync', {is_sync = true})
 _ = s:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 s:insert{1}
  | ---
  | - [1]
@@ -25,3 +28,6 @@ test_run:cmd('restart server default')
 box.space.sync:drop()
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-5288-qsync-recovery.test.lua b/test/replication/gh-5288-qsync-recovery.test.lua
index 00bff7b87..2455f7278 100644
--- a/test/replication/gh-5288-qsync-recovery.test.lua
+++ b/test/replication/gh-5288-qsync-recovery.test.lua
@@ -5,7 +5,9 @@ test_run = require('test_run').new()
 --
 s = box.schema.space.create('sync', {is_sync = true})
 _ = s:create_index('pk')
+box.ctl.promote()
 s:insert{1}
 box.snapshot()
 test_run:cmd('restart server default')
 box.space.sync:drop()
+box.ctl.demote()
diff --git a/test/replication/gh-5298-qsync-recovery-snap.result b/test/replication/gh-5298-qsync-recovery-snap.result
index 922831552..0883fe5f5 100644
--- a/test/replication/gh-5298-qsync-recovery-snap.result
+++ b/test/replication/gh-5298-qsync-recovery-snap.result
@@ -17,6 +17,9 @@ _ = box.schema.space.create('sync', {is_sync = true, engine = engine})
 _ = box.space.sync:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 for i = 1, 10 do box.space.sync:replace{i} end
  | ---
  | ...
@@ -98,3 +101,6 @@ box.space.sync:drop()
 box.space.loc:drop()
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-5298-qsync-recovery-snap.test.lua b/test/replication/gh-5298-qsync-recovery-snap.test.lua
index 187f60d75..084cde963 100644
--- a/test/replication/gh-5298-qsync-recovery-snap.test.lua
+++ b/test/replication/gh-5298-qsync-recovery-snap.test.lua
@@ -8,6 +8,7 @@ engine = test_run:get_cfg('engine')
 --
 _ = box.schema.space.create('sync', {is_sync = true, engine = engine})
 _ = box.space.sync:create_index('pk')
+box.ctl.promote()
 for i = 1, 10 do box.space.sync:replace{i} end
 
 -- Local rows could affect this by increasing the signature.
@@ -46,3 +47,4 @@ box.cfg{
 }
 box.space.sync:drop()
 box.space.loc:drop()
+box.ctl.demote()
diff --git a/test/replication/gh-5426-election-on-off.result b/test/replication/gh-5426-election-on-off.result
index 7444ef7f2..2bdc17ec6 100644
--- a/test/replication/gh-5426-election-on-off.result
+++ b/test/replication/gh-5426-election-on-off.result
@@ -168,6 +168,9 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
 box.schema.user.revoke('guest', 'super')
  | ---
  | ...
diff --git a/test/replication/gh-5426-election-on-off.test.lua b/test/replication/gh-5426-election-on-off.test.lua
index bdf06903b..6277e9ef2 100644
--- a/test/replication/gh-5426-election-on-off.test.lua
+++ b/test/replication/gh-5426-election-on-off.test.lua
@@ -69,4 +69,5 @@ box.cfg{
     election_mode = old_election_mode,                                          \
     replication_timeout = old_replication_timeout,                              \
 }
+box.ctl.demote()
 box.schema.user.revoke('guest', 'super')
diff --git a/test/replication/gh-5433-election-restart-recovery.result b/test/replication/gh-5433-election-restart-recovery.result
index f8f32416e..ed63ff409 100644
--- a/test/replication/gh-5433-election-restart-recovery.result
+++ b/test/replication/gh-5433-election-restart-recovery.result
@@ -169,6 +169,9 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
 box.schema.user.revoke('guest', 'super')
  | ---
  | ...
diff --git a/test/replication/gh-5433-election-restart-recovery.test.lua b/test/replication/gh-5433-election-restart-recovery.test.lua
index 4aff000bf..ae1f42c4d 100644
--- a/test/replication/gh-5433-election-restart-recovery.test.lua
+++ b/test/replication/gh-5433-election-restart-recovery.test.lua
@@ -84,4 +84,5 @@ box.cfg{
     election_mode = old_election_mode,                                          \
     replication_timeout = old_replication_timeout,                              \
 }
+box.ctl.demote()
 box.schema.user.revoke('guest', 'super')
diff --git a/test/replication/gh-5435-qsync-clear-synchro-queue-commit-all.result b/test/replication/gh-5435-qsync-clear-synchro-queue-commit-all.result
index 2699231e5..20fab4072 100644
--- a/test/replication/gh-5435-qsync-clear-synchro-queue-commit-all.result
+++ b/test/replication/gh-5435-qsync-clear-synchro-queue-commit-all.result
@@ -49,6 +49,9 @@ _ = box.schema.space.create('test', {is_sync=true})
 _ = box.space.test:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 
 -- Fill the limbo with pending entries. 3 mustn't receive them yet.
 test_run:cmd('stop server election_replica3')
diff --git a/test/replication/gh-5435-qsync-clear-synchro-queue-commit-all.test.lua b/test/replication/gh-5435-qsync-clear-synchro-queue-commit-all.test.lua
index 03705d96c..ec0f1d77e 100644
--- a/test/replication/gh-5435-qsync-clear-synchro-queue-commit-all.test.lua
+++ b/test/replication/gh-5435-qsync-clear-synchro-queue-commit-all.test.lua
@@ -21,6 +21,7 @@ box.ctl.wait_rw()
 
 _ = box.schema.space.create('test', {is_sync=true})
 _ = box.space.test:create_index('pk')
+box.ctl.promote()
 
 -- Fill the limbo with pending entries. 3 mustn't receive them yet.
 test_run:cmd('stop server election_replica3')
diff --git a/test/replication/gh-5438-raft-state.result b/test/replication/gh-5438-raft-state.result
index 6985f026a..68b6bfad8 100644
--- a/test/replication/gh-5438-raft-state.result
+++ b/test/replication/gh-5438-raft-state.result
@@ -47,6 +47,9 @@ end)
  | ...
 
 -- Cleanup.
+box.ctl.demote()
+ | ---
+ | ...
 box.cfg{election_mode = old_election_mode}
  | ---
  | ...
diff --git a/test/replication/gh-5438-raft-state.test.lua b/test/replication/gh-5438-raft-state.test.lua
index 60c3366c1..cf0f4ca23 100644
--- a/test/replication/gh-5438-raft-state.test.lua
+++ b/test/replication/gh-5438-raft-state.test.lua
@@ -22,6 +22,7 @@ test_run:wait_cond(function()\
 end)
 
 -- Cleanup.
+box.ctl.demote()
 box.cfg{election_mode = old_election_mode}
 test_run:cmd('stop server replica')
 test_run:cmd('delete server replica')
diff --git a/test/replication/gh-5446-qsync-eval-quorum.result b/test/replication/gh-5446-qsync-eval-quorum.result
index 5f83b248c..1173128a7 100644
--- a/test/replication/gh-5446-qsync-eval-quorum.result
+++ b/test/replication/gh-5446-qsync-eval-quorum.result
@@ -88,6 +88,9 @@ s = box.schema.space.create('sync', {is_sync = true, engine = engine})
 _ = s:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 
 -- Only one master node -> 1/2 + 1 = 1
 s:insert{1} -- should pass
@@ -343,3 +346,7 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
+
diff --git a/test/replication/gh-5446-qsync-eval-quorum.test.lua b/test/replication/gh-5446-qsync-eval-quorum.test.lua
index 6b9e324ed..b969df836 100644
--- a/test/replication/gh-5446-qsync-eval-quorum.test.lua
+++ b/test/replication/gh-5446-qsync-eval-quorum.test.lua
@@ -37,6 +37,7 @@ end
 -- Create a sync space we will operate on
 s = box.schema.space.create('sync', {is_sync = true, engine = engine})
 _ = s:create_index('pk')
+box.ctl.promote()
 
 -- Only one master node -> 1/2 + 1 = 1
 s:insert{1} -- should pass
@@ -135,3 +136,5 @@ box.cfg{
     replication_synchro_quorum = old_synchro_quorum,                            \
     replication_synchro_timeout = old_synchro_timeout,                          \
 }
+box.ctl.demote()
+
diff --git a/test/replication/gh-5506-election-on-off.result b/test/replication/gh-5506-election-on-off.result
index b8abd7ecd..a7f2b6a9c 100644
--- a/test/replication/gh-5506-election-on-off.result
+++ b/test/replication/gh-5506-election-on-off.result
@@ -138,3 +138,6 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-5506-election-on-off.test.lua b/test/replication/gh-5506-election-on-off.test.lua
index 476b00ec0..f8915c333 100644
--- a/test/replication/gh-5506-election-on-off.test.lua
+++ b/test/replication/gh-5506-election-on-off.test.lua
@@ -66,3 +66,4 @@ box.cfg{
     election_mode = old_election_mode,                                          \
     replication_timeout = old_replication_timeout,                              \
 }
+box.ctl.demote()
diff --git a/test/replication/gh-5566-final-join-synchro.result b/test/replication/gh-5566-final-join-synchro.result
index a09882ba6..c5ae2f283 100644
--- a/test/replication/gh-5566-final-join-synchro.result
+++ b/test/replication/gh-5566-final-join-synchro.result
@@ -12,6 +12,9 @@ _ = box.schema.space.create('sync', {is_sync=true})
 _ = box.space.sync:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 
 box.schema.user.grant('guest', 'replication')
  | ---
@@ -137,3 +140,6 @@ test_run:cleanup_cluster()
 box.schema.user.revoke('guest', 'replication')
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-5566-final-join-synchro.test.lua b/test/replication/gh-5566-final-join-synchro.test.lua
index 2db2c742f..25f411407 100644
--- a/test/replication/gh-5566-final-join-synchro.test.lua
+++ b/test/replication/gh-5566-final-join-synchro.test.lua
@@ -5,6 +5,7 @@ test_run = require('test_run').new()
 --
 _ = box.schema.space.create('sync', {is_sync=true})
 _ = box.space.sync:create_index('pk')
+box.ctl.promote()
 
 box.schema.user.grant('guest', 'replication')
 box.schema.user.grant('guest', 'write', 'space', 'sync')
@@ -59,3 +60,4 @@ box.cfg{\
 box.space.sync:drop()
 test_run:cleanup_cluster()
 box.schema.user.revoke('guest', 'replication')
+box.ctl.demote()
diff --git a/test/replication/gh-5874-qsync-txn-recovery.result b/test/replication/gh-5874-qsync-txn-recovery.result
index 73f903ca7..01328a9e3 100644
--- a/test/replication/gh-5874-qsync-txn-recovery.result
+++ b/test/replication/gh-5874-qsync-txn-recovery.result
@@ -31,6 +31,9 @@ sync = box.schema.create_space('sync', {is_sync = true, engine = engine})
 _ = sync:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 
 -- The transaction fails, but is written to the log anyway.
 box.begin() async:insert{1} sync:insert{1} box.commit()
@@ -160,3 +163,6 @@ sync:drop()
 loc:drop()
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-5874-qsync-txn-recovery.test.lua b/test/replication/gh-5874-qsync-txn-recovery.test.lua
index f35eb68de..6ddf164ac 100644
--- a/test/replication/gh-5874-qsync-txn-recovery.test.lua
+++ b/test/replication/gh-5874-qsync-txn-recovery.test.lua
@@ -12,6 +12,7 @@ async = box.schema.create_space('async', {engine = engine})
 _ = async:create_index('pk')
 sync = box.schema.create_space('sync', {is_sync = true, engine = engine})
 _ = sync:create_index('pk')
+box.ctl.promote()
 
 -- The transaction fails, but is written to the log anyway.
 box.begin() async:insert{1} sync:insert{1} box.commit()
@@ -82,3 +83,4 @@ loc:select()
 async:drop()
 sync:drop()
 loc:drop()
+box.ctl.demote()
diff --git a/test/replication/gh-6032-promote-wal-write.result b/test/replication/gh-6032-promote-wal-write.result
index 246c7974f..03112fb8d 100644
--- a/test/replication/gh-6032-promote-wal-write.result
+++ b/test/replication/gh-6032-promote-wal-write.result
@@ -67,3 +67,6 @@ box.cfg{\
 box.space.sync:drop()
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-6032-promote-wal-write.test.lua b/test/replication/gh-6032-promote-wal-write.test.lua
index 8c1859083..9a036a8b4 100644
--- a/test/replication/gh-6032-promote-wal-write.test.lua
+++ b/test/replication/gh-6032-promote-wal-write.test.lua
@@ -26,3 +26,4 @@ box.cfg{\
     replication_synchro_timeout = replication_synchro_timeout,\
 }
 box.space.sync:drop()
+box.ctl.demote()
diff --git a/test/replication/gh-6034-limbo-ownership.result b/test/replication/gh-6034-limbo-ownership.result
new file mode 100644
index 000000000..e412b8d53
--- /dev/null
+++ b/test/replication/gh-6034-limbo-ownership.result
@@ -0,0 +1,189 @@
+-- test-run result file version 2
+test_run = require('test_run').new()
+ | ---
+ | ...
+fiber = require('fiber')
+ | ---
+ | ...
+
+--
+-- gh-6034: test that transactional limbo isn't accessible without a promotion.
+--
+synchro_quorum = box.cfg.replication_synchro_quorum
+ | ---
+ | ...
+election_mode = box.cfg.election_mode
+ | ---
+ | ...
+box.cfg{replication_synchro_quorum = 1, election_mode='off'}
+ | ---
+ | ...
+
+_ = box.schema.space.create('async'):create_index('pk')
+ | ---
+ | ...
+_ = box.schema.space.create('sync', {is_sync=true}):create_index('pk')
+ | ---
+ | ...
+
+-- Limbo is initially unclaimed, everyone is writeable.
+assert(not box.info.ro)
+ | ---
+ | - true
+ | ...
+assert(box.info.synchro.queue.owner == 0)
+ | ---
+ | - true
+ | ...
+box.space.async:insert{1} -- success.
+ | ---
+ | - [1]
+ | ...
+-- Synchro spaces aren't writeable
+box.space.sync:insert{1} -- error.
+ | ---
+ | - error: The synchronous transaction queue doesn't belong to any instance
+ | ...
+
+box.ctl.promote()
+ | ---
+ | ...
+assert(not box.info.ro)
+ | ---
+ | - true
+ | ...
+assert(box.info.synchro.queue.owner == box.info.id)
+ | ---
+ | - true
+ | ...
+box.space.sync:insert{1} -- success.
+ | ---
+ | - [1]
+ | ...
+
+-- Everyone but the limbo owner is read-only.
+box.schema.user.grant('guest', 'replication')
+ | ---
+ | ...
+test_run:cmd('create server replica with rpl_master=default,\
+                                         script="replication/replica.lua"')
+ | ---
+ | - true
+ | ...
+test_run:cmd('start server replica with wait=True, wait_load=True')
+ | ---
+ | - true
+ | ...
+test_run:cmd('set variable rpl_listen to "replica.listen"')
+ | ---
+ | - true
+ | ...
+orig_replication = box.cfg.replication
+ | ---
+ | ...
+box.cfg{replication=rpl_listen}
+ | ---
+ | ...
+
+test_run:switch('replica')
+ | ---
+ | - true
+ | ...
+assert(box.info.ro)
+ | ---
+ | - true
+ | ...
+assert(box.info.synchro.queue.owner == test_run:eval('default', 'return box.info.id')[1])
+ | ---
+ | - true
+ | ...
+box.space.async:insert{2} -- failure.
+ | ---
+ | - error: Can't modify data because this instance is in read-only mode.
+ | ...
+
+-- Promotion on the other node. Default should become ro.
+box.ctl.promote()
+ | ---
+ | ...
+assert(not box.info.ro)
+ | ---
+ | - true
+ | ...
+assert(box.info.synchro.queue.owner == box.info.id)
+ | ---
+ | - true
+ | ...
+box.space.sync:insert{2} -- success.
+ | ---
+ | - [2]
+ | ...
+
+test_run:switch('default')
+ | ---
+ | - true
+ | ...
+assert(box.info.ro)
+ | ---
+ | - true
+ | ...
+assert(box.info.synchro.queue.owner == test_run:eval('replica', 'return box.info.id')[1])
+ | ---
+ | - true
+ | ...
+box.space.sync:insert{3} -- failure.
+ | ---
+ | - error: Can't modify data because this instance is in read-only mode.
+ | ...
+
+box.ctl.promote()
+ | ---
+ | ...
+box.ctl.demote()
+ | ---
+ | ...
+assert(not box.info.ro)
+ | ---
+ | - true
+ | ...
+box.space.sync:insert{3} -- still fails.
+ | ---
+ | - error: The synchronous transaction queue doesn't belong to any instance
+ | ...
+assert(box.info.synchro.queue.owner == 0)
+ | ---
+ | - true
+ | ...
+box.space.async:insert{3} -- success.
+ | ---
+ | - [3]
+ | ...
+
+-- Cleanup.
+box.ctl.demote()
+ | ---
+ | ...
+test_run:cmd('stop server replica')
+ | ---
+ | - true
+ | ...
+test_run:cmd('delete server replica')
+ | ---
+ | - true
+ | ...
+box.schema.user.revoke('guest', 'replication')
+ | ---
+ | ...
+box.space.sync:drop()
+ | ---
+ | ...
+box.space.async:drop()
+ | ---
+ | ...
+box.cfg{\
+    replication_synchro_quorum = synchro_quorum,\
+    election_mode = election_mode,\
+    replication = orig_replication,\
+}
+ | ---
+ | ...
diff --git a/test/replication/gh-6034-limbo-ownership.test.lua b/test/replication/gh-6034-limbo-ownership.test.lua
new file mode 100644
index 000000000..c17e12fa4
--- /dev/null
+++ b/test/replication/gh-6034-limbo-ownership.test.lua
@@ -0,0 +1,69 @@
+test_run = require('test_run').new()
+fiber = require('fiber')
+
+--
+-- gh-6034: test that transactional limbo isn't accessible without a promotion.
+--
+synchro_quorum = box.cfg.replication_synchro_quorum
+election_mode = box.cfg.election_mode
+box.cfg{replication_synchro_quorum = 1, election_mode='off'}
+
+_ = box.schema.space.create('async'):create_index('pk')
+_ = box.schema.space.create('sync', {is_sync=true}):create_index('pk')
+
+-- Limbo is initially unclaimed, everyone is writeable.
+assert(not box.info.ro)
+assert(box.info.synchro.queue.owner == 0)
+box.space.async:insert{1} -- success.
+-- Synchro spaces aren't writeable
+box.space.sync:insert{1} -- error.
+
+box.ctl.promote()
+assert(not box.info.ro)
+assert(box.info.synchro.queue.owner == box.info.id)
+box.space.sync:insert{1} -- success.
+
+-- Everyone but the limbo owner is read-only.
+box.schema.user.grant('guest', 'replication')
+test_run:cmd('create server replica with rpl_master=default,\
+                                         script="replication/replica.lua"')
+test_run:cmd('start server replica with wait=True, wait_load=True')
+test_run:cmd('set variable rpl_listen to "replica.listen"')
+orig_replication = box.cfg.replication
+box.cfg{replication=rpl_listen}
+
+test_run:switch('replica')
+assert(box.info.ro)
+assert(box.info.synchro.queue.owner == test_run:eval('default', 'return box.info.id')[1])
+box.space.async:insert{2} -- failure.
+
+-- Promotion on the other node. Default should become ro.
+box.ctl.promote()
+assert(not box.info.ro)
+assert(box.info.synchro.queue.owner == box.info.id)
+box.space.sync:insert{2} -- success.
+
+test_run:switch('default')
+assert(box.info.ro)
+assert(box.info.synchro.queue.owner == test_run:eval('replica', 'return box.info.id')[1])
+box.space.sync:insert{3} -- failure.
+
+box.ctl.promote()
+box.ctl.demote()
+assert(not box.info.ro)
+box.space.sync:insert{3} -- still fails.
+assert(box.info.synchro.queue.owner == 0)
+box.space.async:insert{3} -- success.
+
+-- Cleanup.
+box.ctl.demote()
+test_run:cmd('stop server replica')
+test_run:cmd('delete server replica')
+box.schema.user.revoke('guest', 'replication')
+box.space.sync:drop()
+box.space.async:drop()
+box.cfg{\
+    replication_synchro_quorum = synchro_quorum,\
+    election_mode = election_mode,\
+    replication = orig_replication,\
+}
diff --git a/test/replication/gh-6034-promote-bump-term.result b/test/replication/gh-6034-promote-bump-term.result
index 20e352922..e5087507c 100644
--- a/test/replication/gh-6034-promote-bump-term.result
+++ b/test/replication/gh-6034-promote-bump-term.result
@@ -32,6 +32,9 @@ assert(box.info.election.term == term + 2)
  | ...
 
 -- Cleanup.
+box.ctl.demote()
+ | ---
+ | ...
 box.cfg{election_mode=election_mode}
  | ---
  | ...
diff --git a/test/replication/gh-6034-promote-bump-term.test.lua b/test/replication/gh-6034-promote-bump-term.test.lua
index 5847dbb8f..af18853f3 100644
--- a/test/replication/gh-6034-promote-bump-term.test.lua
+++ b/test/replication/gh-6034-promote-bump-term.test.lua
@@ -13,4 +13,5 @@ box.ctl.promote()
 assert(box.info.election.term == term + 2)
 
 -- Cleanup.
+box.ctl.demote()
 box.cfg{election_mode=election_mode}
diff --git a/test/replication/gh-6057-qsync-confirm-async-no-wal.result b/test/replication/gh-6057-qsync-confirm-async-no-wal.result
index 23c77729b..e7beefb2a 100644
--- a/test/replication/gh-6057-qsync-confirm-async-no-wal.result
+++ b/test/replication/gh-6057-qsync-confirm-async-no-wal.result
@@ -40,6 +40,10 @@ _ = s2:create_index('pk')
  | ---
  | ...
 
+box.ctl.promote()
+ | ---
+ | ...
+
 errinj = box.error.injection
  | ---
  | ...
@@ -161,3 +165,6 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/gh-6057-qsync-confirm-async-no-wal.test.lua b/test/replication/gh-6057-qsync-confirm-async-no-wal.test.lua
index a11ddc042..bb459ea02 100644
--- a/test/replication/gh-6057-qsync-confirm-async-no-wal.test.lua
+++ b/test/replication/gh-6057-qsync-confirm-async-no-wal.test.lua
@@ -21,6 +21,8 @@ _ = s:create_index('pk')
 s2 = box.schema.create_space('test2')
 _ = s2:create_index('pk')
 
+box.ctl.promote()
+
 errinj = box.error.injection
 
 function create_hanging_async_after_confirm(sync_key, async_key1, async_key2)   \
@@ -86,3 +88,4 @@ box.cfg{
     replication_synchro_quorum = old_synchro_quorum,                            \
     replication_synchro_timeout = old_synchro_timeout,                          \
 }
+box.ctl.demote()
diff --git a/test/replication/hang_on_synchro_fail.result b/test/replication/hang_on_synchro_fail.result
index 9f6fac00b..dda15af20 100644
--- a/test/replication/hang_on_synchro_fail.result
+++ b/test/replication/hang_on_synchro_fail.result
@@ -19,6 +19,9 @@ _ = box.schema.space.create('sync', {is_sync=true})
 _ = box.space.sync:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 
 old_synchro_quorum = box.cfg.replication_synchro_quorum
  | ---
@@ -127,4 +130,7 @@ box.space.sync:drop()
 box.schema.user.revoke('guest', 'replication')
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
 
diff --git a/test/replication/hang_on_synchro_fail.test.lua b/test/replication/hang_on_synchro_fail.test.lua
index 6c3b09fab..f0d494eae 100644
--- a/test/replication/hang_on_synchro_fail.test.lua
+++ b/test/replication/hang_on_synchro_fail.test.lua
@@ -8,6 +8,7 @@ box.schema.user.grant('guest', 'replication')
 
 _ = box.schema.space.create('sync', {is_sync=true})
 _ = box.space.sync:create_index('pk')
+box.ctl.promote()
 
 old_synchro_quorum = box.cfg.replication_synchro_quorum
 box.cfg{replication_synchro_quorum=3}
@@ -54,4 +55,5 @@ box.cfg{replication_synchro_quorum=old_synchro_quorum,\
         replication_synchro_timeout=old_synchro_timeout}
 box.space.sync:drop()
 box.schema.user.revoke('guest', 'replication')
+box.ctl.demote()
 
diff --git a/test/replication/qsync_advanced.result b/test/replication/qsync_advanced.result
index 94b19b1f2..72ac0c326 100644
--- a/test/replication/qsync_advanced.result
+++ b/test/replication/qsync_advanced.result
@@ -72,6 +72,9 @@ _ = box.schema.space.create('sync', {is_sync=true, engine=engine})
 _ = box.space.sync:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 -- Testcase body.
 box.space.sync:insert{1} -- success
  | ---
@@ -468,6 +471,9 @@ box.space.sync:select{} -- 1
 box.cfg{read_only=false} -- promote replica to master
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 test_run:switch('default')
  | ---
  | - true
@@ -508,6 +514,9 @@ test_run:switch('default')
 box.cfg{read_only=false}
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 test_run:switch('replica')
  | ---
  | - true
@@ -781,3 +790,6 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/qsync_advanced.test.lua b/test/replication/qsync_advanced.test.lua
index 058ece602..37c285b8d 100644
--- a/test/replication/qsync_advanced.test.lua
+++ b/test/replication/qsync_advanced.test.lua
@@ -30,6 +30,7 @@ test_run:switch('default')
 box.cfg{replication_synchro_quorum=NUM_INSTANCES, replication_synchro_timeout=1000}
 _ = box.schema.space.create('sync', {is_sync=true, engine=engine})
 _ = box.space.sync:create_index('pk')
+box.ctl.promote()
 -- Testcase body.
 box.space.sync:insert{1} -- success
 test_run:cmd('switch replica')
@@ -170,6 +171,7 @@ box.space.sync:select{} -- 1
 test_run:switch('replica')
 box.space.sync:select{} -- 1
 box.cfg{read_only=false} -- promote replica to master
+box.ctl.promote()
 test_run:switch('default')
 box.cfg{read_only=true} -- demote master to replica
 test_run:switch('replica')
@@ -181,6 +183,7 @@ box.space.sync:select{} -- 1, 2
 -- Revert cluster configuration.
 test_run:switch('default')
 box.cfg{read_only=false}
+box.ctl.promote()
 test_run:switch('replica')
 box.cfg{read_only=true}
 -- Testcase cleanup.
@@ -279,3 +282,4 @@ box.cfg{
     replication_synchro_quorum = orig_synchro_quorum,                           \
     replication_synchro_timeout = orig_synchro_timeout,                         \
 }
+box.ctl.demote()
diff --git a/test/replication/qsync_basic.result b/test/replication/qsync_basic.result
index 7e711ba13..bbdfc42fe 100644
--- a/test/replication/qsync_basic.result
+++ b/test/replication/qsync_basic.result
@@ -14,6 +14,9 @@ s1.is_sync
 pk = s1:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 box.begin() s1:insert({1}) s1:insert({2}) box.commit()
  | ---
  | ...
@@ -645,19 +648,12 @@ test_run:switch('default')
  | ---
  | - true
  | ...
-box.cfg{replication_synchro_quorum = 3, replication_synchro_timeout = 1000}
- | ---
- | ...
-f = fiber.create(function() box.space.sync:replace{1} end)
+box.ctl.demote()
  | ---
  | ...
-test_run:wait_lsn('replica', 'default')
+box.space.sync:replace{1}
  | ---
- | ...
-
-test_run:switch('replica')
- | ---
- | - true
+ | - error: The synchronous transaction queue doesn't belong to any instance
  | ...
 function skip_row() return nil end
  | ---
@@ -674,26 +670,22 @@ box.space.sync:replace{2}
 box.space.sync:before_replace(nil, skip_row)
  | ---
  | ...
-assert(box.space.sync:get{2} == nil)
+assert(box.space.sync:get{1} == nil)
  | ---
  | - true
  | ...
-assert(box.space.sync:get{1} ~= nil)
+assert(box.space.sync:get{2} == nil)
  | ---
  | - true
  | ...
-
-test_run:switch('default')
+assert(box.info.lsn == old_lsn + 1)
  | ---
  | - true
  | ...
-box.cfg{replication_synchro_quorum = 2}
+box.ctl.promote()
  | ---
  | ...
-test_run:wait_cond(function() return f:status() == 'dead' end)
- | ---
- | - true
- | ...
+
 box.space.sync:truncate()
  | ---
  | ...
@@ -758,3 +750,6 @@ box.space.sync:drop()
 box.schema.user.revoke('guest', 'replication')
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/qsync_basic.test.lua b/test/replication/qsync_basic.test.lua
index 75c9b222b..eac465e25 100644
--- a/test/replication/qsync_basic.test.lua
+++ b/test/replication/qsync_basic.test.lua
@@ -6,6 +6,7 @@
 s1 = box.schema.create_space('test1', {is_sync = true})
 s1.is_sync
 pk = s1:create_index('pk')
+box.ctl.promote()
 box.begin() s1:insert({1}) s1:insert({2}) box.commit()
 s1:select{}
 
@@ -253,22 +254,18 @@ box.space.sync:count()
 -- instances, but also works for local rows.
 --
 test_run:switch('default')
-box.cfg{replication_synchro_quorum = 3, replication_synchro_timeout = 1000}
-f = fiber.create(function() box.space.sync:replace{1} end)
-test_run:wait_lsn('replica', 'default')
-
-test_run:switch('replica')
+box.ctl.demote()
+box.space.sync:replace{1}
 function skip_row() return nil end
 old_lsn = box.info.lsn
 _ = box.space.sync:before_replace(skip_row)
 box.space.sync:replace{2}
 box.space.sync:before_replace(nil, skip_row)
+assert(box.space.sync:get{1} == nil)
 assert(box.space.sync:get{2} == nil)
-assert(box.space.sync:get{1} ~= nil)
+assert(box.info.lsn == old_lsn + 1)
+box.ctl.promote()
 
-test_run:switch('default')
-box.cfg{replication_synchro_quorum = 2}
-test_run:wait_cond(function() return f:status() == 'dead' end)
 box.space.sync:truncate()
 
 --
@@ -301,3 +298,4 @@ test_run:cmd('delete server replica')
 box.space.test:drop()
 box.space.sync:drop()
 box.schema.user.revoke('guest', 'replication')
+box.ctl.demote()
diff --git a/test/replication/qsync_errinj.result b/test/replication/qsync_errinj.result
index 635bcf939..cf1e30a90 100644
--- a/test/replication/qsync_errinj.result
+++ b/test/replication/qsync_errinj.result
@@ -35,6 +35,9 @@ _ = box.schema.space.create('sync', {is_sync = true, engine = engine})
 _ = box.space.sync:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 
 --
 -- gh-5100: slow ACK sending shouldn't stun replica for the
@@ -542,3 +545,6 @@ box.space.sync:drop()
 box.schema.user.revoke('guest', 'super')
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/qsync_errinj.test.lua b/test/replication/qsync_errinj.test.lua
index 6a9fd3e1a..e7c85c58c 100644
--- a/test/replication/qsync_errinj.test.lua
+++ b/test/replication/qsync_errinj.test.lua
@@ -12,6 +12,7 @@ test_run:cmd('start server replica with wait=True, wait_load=True')
 
 _ = box.schema.space.create('sync', {is_sync = true, engine = engine})
 _ = box.space.sync:create_index('pk')
+box.ctl.promote()
 
 --
 -- gh-5100: slow ACK sending shouldn't stun replica for the
@@ -222,3 +223,4 @@ test_run:cmd('delete server replica')
 
 box.space.sync:drop()
 box.schema.user.revoke('guest', 'super')
+box.ctl.demote()
diff --git a/test/replication/qsync_snapshots.result b/test/replication/qsync_snapshots.result
index cafdd63c8..ca418b168 100644
--- a/test/replication/qsync_snapshots.result
+++ b/test/replication/qsync_snapshots.result
@@ -57,6 +57,9 @@ _ = box.schema.space.create('sync', {is_sync=true, engine=engine})
 _ = box.space.sync:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 -- Testcase body.
 box.space.sync:insert{1}
  | ---
@@ -299,3 +302,6 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
diff --git a/test/replication/qsync_snapshots.test.lua b/test/replication/qsync_snapshots.test.lua
index 590610974..82c2e3f7c 100644
--- a/test/replication/qsync_snapshots.test.lua
+++ b/test/replication/qsync_snapshots.test.lua
@@ -23,6 +23,7 @@ test_run:switch('default')
 box.cfg{replication_synchro_quorum=NUM_INSTANCES, replication_synchro_timeout=1000}
 _ = box.schema.space.create('sync', {is_sync=true, engine=engine})
 _ = box.space.sync:create_index('pk')
+box.ctl.promote()
 -- Testcase body.
 box.space.sync:insert{1}
 box.space.sync:select{} -- 1
@@ -130,3 +131,4 @@ box.cfg{
     replication_synchro_quorum = orig_synchro_quorum,                           \
     replication_synchro_timeout = orig_synchro_timeout,                         \
 }
+box.ctl.demote()
diff --git a/test/replication/qsync_with_anon.result b/test/replication/qsync_with_anon.result
index 6a2952a32..99c6fb902 100644
--- a/test/replication/qsync_with_anon.result
+++ b/test/replication/qsync_with_anon.result
@@ -57,6 +57,9 @@ _ = box.schema.space.create('sync', {is_sync=true, engine=engine})
 _ = box.space.sync:create_index('pk')
  | ---
  | ...
+box.ctl.promote()
+ | ---
+ | ...
 -- Testcase body.
 test_run:switch('default')
  | ---
@@ -220,6 +223,9 @@ box.cfg{
 }
  | ---
  | ...
+box.ctl.demote()
+ | ---
+ | ...
 test_run:cleanup_cluster()
  | ---
  | ...
diff --git a/test/replication/qsync_with_anon.test.lua b/test/replication/qsync_with_anon.test.lua
index d7ecaa107..e73880ec7 100644
--- a/test/replication/qsync_with_anon.test.lua
+++ b/test/replication/qsync_with_anon.test.lua
@@ -22,6 +22,7 @@ test_run:switch('default')
 box.cfg{replication_synchro_quorum=NUM_INSTANCES, replication_synchro_timeout=1000}
 _ = box.schema.space.create('sync', {is_sync=true, engine=engine})
 _ = box.space.sync:create_index('pk')
+box.ctl.promote()
 -- Testcase body.
 test_run:switch('default')
 box.space.sync:insert{1} -- success
@@ -81,4 +82,5 @@ box.cfg{
     replication_synchro_quorum = orig_synchro_quorum,                           \
     replication_synchro_timeout = orig_synchro_timeout,                         \
 }
+box.ctl.demote()
 test_run:cleanup_cluster()
diff --git a/test/replication/suite.cfg b/test/replication/suite.cfg
index eb88b9420..977deeb40 100644
--- a/test/replication/suite.cfg
+++ b/test/replication/suite.cfg
@@ -47,6 +47,7 @@
     "gh-5613-bootstrap-prefer-booted.test.lua": {},
     "gh-6027-applier-error-show.test.lua": {},
     "gh-6032-promote-wal-write.test.lua": {},
+    "gh-6034-limbo-ownership.test.lua": {},
     "gh-6034-promote-bump-term.test.lua": {},
     "gh-6057-qsync-confirm-async-no-wal.test.lua": {},
     "gh-6094-rs-uuid-mismatch.test.lua": {},
-- 
2.30.1 (Apple Git-130)