[Tarantool-patches] [PATCH v2 5/8] replication: forbid implicit limbo owner transition

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

Forbid limbo ownership transition without an explicit promote.
Make it so that synchronous transactions may be committed only after it
is claimed by some instance via a PROMOTE request.

Make everyone but the limbo owner read-only even when the limbo is
empty.

Part-of #6034

@TarantoolBot document
Title: synchronous replication changes

`box.info.synchro.queue` receives a new field: `owner`. It's a replica
id of the instance owning the synchronous transaction queue.

Once some instance owns the queue, every other instance becomes
read-only. When the queue is unclaimed, e.g.
`box.info.synchro.queue.owner` is `0`, everyone may be writeable, but
cannot create synchronous transactions.

In order to claim or re-claim the queue, you have to issue
`box.ctl.promote()` on the instance you wish to promote.

When elections are enabled, the instance issues `box.ctl.promote()`
automatically once it wins the elections, no additional actions are
required.
---
 src/box/errcode.h                          |   1 +
 src/box/lua/info.c                         |   4 +-
 src/box/txn_limbo.c                        |  35 ++----
 test/box/alter.result                      |   2 +-
 test/box/error.result                      |   1 +
 test/replication/gh-5440-qsync-ro.result   | 133 ---------------------
 test/replication/gh-5440-qsync-ro.test.lua |  53 --------
 7 files changed, 16 insertions(+), 213 deletions(-)
 delete mode 100644 test/replication/gh-5440-qsync-ro.result
 delete mode 100644 test/replication/gh-5440-qsync-ro.test.lua

diff --git a/src/box/errcode.h b/src/box/errcode.h
index 49aec4bf6..e3943c01d 100644
--- a/src/box/errcode.h
+++ b/src/box/errcode.h
@@ -278,6 +278,7 @@ struct errcode_record {
 	/*223 */_(ER_INTERFERING_PROMOTE,	"Instance with replica id %u was promoted first") \
 	/*224 */_(ER_RAFT_DISABLED,		"Elections were turned off while running box.ctl.promote()")\
 	/*225 */_(ER_TXN_ROLLBACK,		"Transaction was rolled back") \
+	/*226 */_(ER_SYNCHRO_QUEUE_UNCLAIMED,	"The synchronous transaction queue doesn't belong to any instance")\
 
 /*
  * !IMPORTANT! Please follow instructions at start of the file
diff --git a/src/box/lua/info.c b/src/box/lua/info.c
index 0eb48b823..7e3cd0b7d 100644
--- a/src/box/lua/info.c
+++ b/src/box/lua/info.c
@@ -611,9 +611,11 @@ lbox_info_synchro(struct lua_State *L)
 
 	/* Queue information. */
 	struct txn_limbo *queue = &txn_limbo;
-	lua_createtable(L, 0, 1);
+	lua_createtable(L, 0, 2);
 	lua_pushnumber(L, queue->len);
 	lua_setfield(L, -2, "len");
+	lua_pushnumber(L, queue->owner_id);
+	lua_setfield(L, -2, "owner");
 	lua_setfield(L, -2, "queue");
 
 	return 1;
diff --git a/src/box/txn_limbo.c b/src/box/txn_limbo.c
index a5d1df00c..203dbe856 100644
--- a/src/box/txn_limbo.c
+++ b/src/box/txn_limbo.c
@@ -55,7 +55,8 @@ txn_limbo_create(struct txn_limbo *limbo)
 bool
 txn_limbo_is_ro(struct txn_limbo *limbo)
 {
-	return limbo->owner_id != instance_id && !txn_limbo_is_empty(limbo);
+	return limbo->owner_id != REPLICA_ID_NIL &&
+	       limbo->owner_id != instance_id;
 }
 
 struct txn_limbo_entry *
@@ -95,18 +96,13 @@ txn_limbo_append(struct txn_limbo *limbo, uint32_t id, struct txn *txn)
 	}
 	if (id == 0)
 		id = instance_id;
-	bool make_ro = false;
-	if (limbo->owner_id != id) {
-		if (rlist_empty(&limbo->queue)) {
-			limbo->owner_id = id;
-			limbo->confirmed_lsn = 0;
-			if (id != instance_id)
-				make_ro = true;
-		} else {
-			diag_set(ClientError, ER_UNCOMMITTED_FOREIGN_SYNC_TXNS,
-				 limbo->owner_id);
-			return NULL;
-		}
+	if  (limbo->owner_id == REPLICA_ID_NIL) {
+		diag_set(ClientError, ER_SYNCHRO_QUEUE_UNCLAIMED);
+		return NULL;
+	} else if (limbo->owner_id != id) {
+		diag_set(ClientError, ER_UNCOMMITTED_FOREIGN_SYNC_TXNS,
+			 limbo->owner_id);
+		return NULL;
 	}
 	size_t size;
 	struct txn_limbo_entry *e = region_alloc_object(&txn->region,
@@ -122,12 +118,6 @@ txn_limbo_append(struct txn_limbo *limbo, uint32_t id, struct txn *txn)
 	e->is_rollback = false;
 	rlist_add_tail_entry(&limbo->queue, e, in_queue);
 	limbo->len++;
-	/*
-	 * We added new entries from a remote instance to an empty limbo.
-	 * Time to make this instance read-only.
-	 */
-	if (make_ro)
-		box_update_ro_summary();
 	return e;
 }
 
@@ -432,9 +422,6 @@ txn_limbo_read_confirm(struct txn_limbo *limbo, int64_t lsn)
 		assert(e->txn->signature >= 0);
 		txn_complete_success(e->txn);
 	}
-	/* Update is_ro once the limbo is clear. */
-	if (txn_limbo_is_empty(limbo))
-		box_update_ro_summary();
 }
 
 /**
@@ -482,9 +469,6 @@ txn_limbo_read_rollback(struct txn_limbo *limbo, int64_t lsn)
 		if (e == last_rollback)
 			break;
 	}
-	/* Update is_ro once the limbo is clear. */
-	if (txn_limbo_is_empty(limbo))
-		box_update_ro_summary();
 }
 
 void
@@ -515,6 +499,7 @@ txn_limbo_read_promote(struct txn_limbo *limbo, uint32_t replica_id,
 	txn_limbo_read_rollback(limbo, lsn + 1);
 	assert(txn_limbo_is_empty(&txn_limbo));
 	limbo->owner_id = replica_id;
+	box_update_ro_summary();
 	limbo->confirmed_lsn = 0;
 }
 
diff --git a/test/box/alter.result b/test/box/alter.result
index a7bffce10..6a64f6b84 100644
--- a/test/box/alter.result
+++ b/test/box/alter.result
@@ -1464,7 +1464,7 @@ assert(s.is_sync)
 ...
 s:replace{1}
 ---
-- error: Quorum collection for a synchronous transaction is timed out
+- error: The synchronous transaction queue doesn't belong to any instance
 ...
 -- When not specified or nil - ignored.
 s:alter({is_sync = nil})
diff --git a/test/box/error.result b/test/box/error.result
index 062a90399..574521a14 100644
--- a/test/box/error.result
+++ b/test/box/error.result
@@ -444,6 +444,7 @@ t;
  |   223: box.error.INTERFERING_PROMOTE
  |   224: box.error.RAFT_DISABLED
  |   225: box.error.TXN_ROLLBACK
+ |   226: box.error.LIMBO_UNCLAIMED
  | ...
 
 test_run:cmd("setopt delimiter ''");
diff --git a/test/replication/gh-5440-qsync-ro.result b/test/replication/gh-5440-qsync-ro.result
deleted file mode 100644
index 1ece26a42..000000000
--- a/test/replication/gh-5440-qsync-ro.result
+++ /dev/null
@@ -1,133 +0,0 @@
--- test-run result file version 2
---
--- gh-5440 everyone but the limbo owner is read-only on non-empty limbo.
---
-env = require('test_run')
- | ---
- | ...
-test_run = env.new()
- | ---
- | ...
-fiber = require('fiber')
- | ---
- | ...
-
-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
- | ...
-
-_ = box.schema.space.create('test', {is_sync=true})
- | ---
- | ...
-_ = box.space.test:create_index('pk')
- | ---
- | ...
-
-old_synchro_quorum = box.cfg.replication_synchro_quorum
- | ---
- | ...
-old_synchro_timeout = box.cfg.replication_synchro_timeout
- | ---
- | ...
-
--- Make sure that the master stalls on commit leaving the limbo non-empty.
-box.cfg{replication_synchro_quorum=3, replication_synchro_timeout=1000}
- | ---
- | ...
-
-f = fiber.new(function() box.space.test:insert{1} end)
- | ---
- | ...
-f:status()
- | ---
- | - suspended
- | ...
-
--- Wait till replica's limbo is non-empty.
-test_run:wait_lsn('replica', 'default')
- | ---
- | ...
-test_run:cmd('switch replica')
- | ---
- | - true
- | ...
-
-box.info.ro
- | ---
- | - true
- | ...
-box.space.test:insert{2}
- | ---
- | - error: Can't modify data because this instance is in read-only mode.
- | ...
-success = false
- | ---
- | ...
-f = require('fiber').new(function() box.ctl.wait_rw() success = true end)
- | ---
- | ...
-f:status()
- | ---
- | - suspended
- | ...
-
-test_run:cmd('switch default')
- | ---
- | - true
- | ...
-
--- Empty the limbo.
-box.cfg{replication_synchro_quorum=2}
- | ---
- | ...
-
-test_run:cmd('switch replica')
- | ---
- | - true
- | ...
-
-test_run:wait_cond(function() return success end)
- | ---
- | - true
- | ...
-box.info.ro
- | ---
- | - false
- | ...
--- Should succeed now.
-box.space.test:insert{2}
- | ---
- | - [2]
- | ...
-
--- Cleanup.
-test_run:cmd('switch default')
- | ---
- | - true
- | ...
-box.cfg{replication_synchro_quorum=old_synchro_quorum,\
-        replication_synchro_timeout=old_synchro_timeout}
- | ---
- | ...
-box.space.test:drop()
- | ---
- | ...
-test_run:cmd('stop server replica')
- | ---
- | - true
- | ...
-test_run:cmd('delete server replica')
- | ---
- | - true
- | ...
-box.schema.user.revoke('guest', 'replication')
- | ---
- | ...
diff --git a/test/replication/gh-5440-qsync-ro.test.lua b/test/replication/gh-5440-qsync-ro.test.lua
deleted file mode 100644
index d63ec9c1e..000000000
--- a/test/replication/gh-5440-qsync-ro.test.lua
+++ /dev/null
@@ -1,53 +0,0 @@
---
--- gh-5440 everyone but the limbo owner is read-only on non-empty limbo.
---
-env = require('test_run')
-test_run = env.new()
-fiber = require('fiber')
-
-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')
-
-_ = box.schema.space.create('test', {is_sync=true})
-_ = box.space.test:create_index('pk')
-
-old_synchro_quorum = box.cfg.replication_synchro_quorum
-old_synchro_timeout = box.cfg.replication_synchro_timeout
-
--- Make sure that the master stalls on commit leaving the limbo non-empty.
-box.cfg{replication_synchro_quorum=3, replication_synchro_timeout=1000}
-
-f = fiber.new(function() box.space.test:insert{1} end)
-f:status()
-
--- Wait till replica's limbo is non-empty.
-test_run:wait_lsn('replica', 'default')
-test_run:cmd('switch replica')
-
-box.info.ro
-box.space.test:insert{2}
-success = false
-f = require('fiber').new(function() box.ctl.wait_rw() success = true end)
-f:status()
-
-test_run:cmd('switch default')
-
--- Empty the limbo.
-box.cfg{replication_synchro_quorum=2}
-
-test_run:cmd('switch replica')
-
-test_run:wait_cond(function() return success end)
-box.info.ro
--- Should succeed now.
-box.space.test:insert{2}
-
--- Cleanup.
-test_run:cmd('switch default')
-box.cfg{replication_synchro_quorum=old_synchro_quorum,\
-        replication_synchro_timeout=old_synchro_timeout}
-box.space.test:drop()
-test_run:cmd('stop server replica')
-test_run:cmd('delete server replica')
-box.schema.user.revoke('guest', 'replication')
-- 
2.30.1 (Apple Git-130)