[Tarantool-patches] [PATCH v2 08/19] replication: add support of qsync to the snapshot machinery

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

From: Leonid Vasiliev <lvasiliev@tarantool.org>

To support qsync replication, the waiting for confirmation of
current "sync" transactions during a timeout has been added to
the snapshot machinery. In the case of rollback or the timeout
expiration, the snapshot will be cancelled.

Closes #4850
---
 src/box/gc.c                       |  12 ++
 src/box/txn_limbo.c                |  81 ++++++++++
 src/box/txn_limbo.h                |  29 ++++
 test/unit/CMakeLists.txt           |   3 +
 test/unit/snap_quorum_delay.cc     | 250 +++++++++++++++++++++++++++++
 test/unit/snap_quorum_delay.result |  12 ++
 6 files changed, 387 insertions(+)
 create mode 100644 test/unit/snap_quorum_delay.cc
 create mode 100644 test/unit/snap_quorum_delay.result

diff --git a/src/box/gc.c b/src/box/gc.c
index 8e8ffea75..170c0a97f 100644
--- a/src/box/gc.c
+++ b/src/box/gc.c
@@ -57,6 +57,9 @@
 #include "engine.h"		/* engine_collect_garbage() */
 #include "wal.h"		/* wal_collect_garbage() */
 #include "checkpoint_schedule.h"
+#include "trigger.h"
+#include "txn.h"
+#include "txn_limbo.h"
 
 struct gc_state gc;
 
@@ -395,6 +398,15 @@ gc_do_checkpoint(bool is_scheduled)
 	rc = wal_begin_checkpoint(&checkpoint);
 	if (rc != 0)
 		goto out;
+
+	/*
+	 * Wait the confirms on all "sync" transactions before
+	 * create a snapshot.
+	 */
+	rc = txn_limbo_wait_confirm(&txn_limbo);
+	if (rc != 0)
+		goto out;
+
 	rc = engine_commit_checkpoint(&checkpoint.vclock);
 	if (rc != 0)
 		goto out;
diff --git a/src/box/txn_limbo.c b/src/box/txn_limbo.c
index b38d82e4f..bee8e8155 100644
--- a/src/box/txn_limbo.c
+++ b/src/box/txn_limbo.c
@@ -231,6 +231,87 @@ txn_limbo_ack(struct txn_limbo *limbo, uint32_t replica_id, int64_t lsn)
 	}
 }
 
+double
+txn_limbo_confirm_timeout(struct txn_limbo *limbo)
+{
+	(void)limbo;
+	return replication_synchro_timeout;
+}
+
+/**
+ * Waitpoint stores information about the progress of confirmation.
+ * In the case of multimaster support, it will store a bitset
+ * or array instead of the boolean.
+ */
+struct confirm_waitpoint {
+	/**
+	 * Variable for wake up the fiber that is waiting for
+	 * the end of confirmation.
+	 */
+	struct fiber_cond confirm_cond;
+	/**
+	 * Result flag.
+	 */
+	bool is_confirm;
+};
+
+static int
+txn_commit_cb(struct trigger *trigger, void *event)
+{
+	(void)event;
+	struct confirm_waitpoint *cwp =
+		(struct confirm_waitpoint *)trigger->data;
+	cwp->is_confirm = true;
+	fiber_cond_signal(&cwp->confirm_cond);
+	return 0;
+}
+
+static int
+txn_rollback_cb(struct trigger *trigger, void *event)
+{
+	(void)event;
+	struct confirm_waitpoint *cwp =
+		(struct confirm_waitpoint *)trigger->data;
+	fiber_cond_signal(&cwp->confirm_cond);
+	return 0;
+}
+
+int
+txn_limbo_wait_confirm(struct txn_limbo *limbo)
+{
+	if (txn_limbo_is_empty(limbo))
+		return 0;
+
+	/* initialization of a waitpoint. */
+	struct confirm_waitpoint cwp;
+	fiber_cond_create(&cwp.confirm_cond);
+	cwp.is_confirm = false;
+
+	/* Set triggers for the last limbo transaction. */
+	struct trigger on_complete;
+	trigger_create(&on_complete, txn_commit_cb, &cwp, NULL);
+	struct trigger on_rollback;
+	trigger_create(&on_rollback, txn_rollback_cb, &cwp, NULL);
+	struct txn_limbo_entry *tle = txn_limbo_last_entry(limbo);
+	txn_on_commit(tle->txn, &on_complete);
+	txn_on_rollback(tle->txn, &on_rollback);
+
+	int rc = fiber_cond_wait_timeout(&cwp.confirm_cond,
+					 txn_limbo_confirm_timeout(limbo));
+	fiber_cond_destroy(&cwp.confirm_cond);
+	if (rc != 0) {
+		/* Clear the triggers if the timeout has been reached. */
+		trigger_clear(&on_complete);
+		trigger_clear(&on_rollback);
+		return -1;
+	}
+	if (!cwp.is_confirm) {
+		/* The transaction has been rolled back. */
+		return -1;
+	}
+	return 0;
+}
+
 void
 txn_limbo_init(void)
 {
diff --git a/src/box/txn_limbo.h b/src/box/txn_limbo.h
index de415cd97..94f224131 100644
--- a/src/box/txn_limbo.h
+++ b/src/box/txn_limbo.h
@@ -166,6 +166,35 @@ txn_limbo_wait_complete(struct txn_limbo *limbo, struct txn_limbo_entry *entry);
 void
 txn_limbo_read_confirm(struct txn_limbo *limbo, int64_t lsn);
 
+/**
+ * Return TRUE if limbo is empty.
+ */
+static inline bool
+txn_limbo_is_empty(struct txn_limbo *limbo)
+{
+	return rlist_empty(&limbo->queue);
+}
+
+/**
+ * Return a pointer to the last txn_limbo_entry of limbo.
+ */
+static inline struct txn_limbo_entry *
+txn_limbo_last_entry(struct txn_limbo *limbo)
+{
+	return rlist_last_entry(&limbo->queue, struct txn_limbo_entry,
+				in_queue);
+}
+
+double
+txn_limbo_confirm_timeout(struct txn_limbo *limbo);
+
+/**
+ * Waiting for confirmation of all "sync" transactions
+ * during confirm timeout or fail.
+ */
+int
+txn_limbo_wait_confirm(struct txn_limbo *limbo);
+
 void
 txn_limbo_init();
 
diff --git a/test/unit/CMakeLists.txt b/test/unit/CMakeLists.txt
index 672122118..419477748 100644
--- a/test/unit/CMakeLists.txt
+++ b/test/unit/CMakeLists.txt
@@ -257,6 +257,9 @@ target_link_libraries(swim_errinj.test unit swim)
 add_executable(merger.test merger.test.c)
 target_link_libraries(merger.test unit core box)
 
+add_executable(snap_quorum_delay.test snap_quorum_delay.cc)
+target_link_libraries(snap_quorum_delay.test box core unit)
+
 #
 # Client for popen.test
 add_executable(popen-child popen-child.c)
diff --git a/test/unit/snap_quorum_delay.cc b/test/unit/snap_quorum_delay.cc
new file mode 100644
index 000000000..7a200673a
--- /dev/null
+++ b/test/unit/snap_quorum_delay.cc
@@ -0,0 +1,250 @@
+/*
+ * Copyright 2010-2020, Tarantool AUTHORS, please see AUTHORS file.
+ *
+ * Redistribution and use in source and iproto forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above
+ *    copyright notice, this list of conditions and the
+ *    following disclaimer.
+ *
+ * 2. Redistributions in iproto form must reproduce the above
+ *    copyright notice, this list of conditions and the following
+ *    disclaimer in the documentation and/or other materials
+ *    provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY <COPYRIGHT HOLDER> ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+ * <COPYRIGHT HOLDER> OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+ * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+ * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+#include "unit.h"
+#include "gc.h"
+#include "memory.h"
+#include "txn.h"
+#include "txn_limbo.h"
+
+/**
+ * This test is only about delay in snapshot machinery (needed
+ * for qsync replication). It doesn't test the snapshot
+ * machinery, txn_limbo or something else and uses some tricks
+ * around txn_limbo.
+ * The logic of the test is as folows:
+ * In fiber_1 ("txn_fiber"):
+ *	- start a transaction.
+ *	- push the transaction to the limbo.
+ *	- start wait confirm (yield).
+ * In fiber_2 ("main"):
+ *	- do a snapshot.
+ *	- start wait while the last transaction
+ *	  from the limbo will be completed.
+ * In fiber_3 ("confirm_fiber"):
+ *	- confirm the transaction (remove the transaction from
+ *				   the limbo and wakeup fiber_1).
+ * In fiber_1 ("txn_fiber"):
+ *	- confirm/rollback/hung the transaction.
+ * In fiber_2 ("main"):
+ *	- check_results
+ */
+
+extern int replication_synchro_quorum;
+extern double replication_synchro_timeout;
+
+namespace /* local symbols */ {
+
+int test_result;
+
+/**
+ * Variations of a transaction completion.
+ */
+enum process_type {
+	TXN_PROCESS_COMMIT,
+	TXN_PROCESS_ROLLBACK,
+	TXN_PROCESS_TIMEOUT
+};
+
+/**
+ * Some fake values needed for work with the limbo
+ * (to push a transaction to the limbo and simulate confirm).
+ */
+const int fake_lsn = 1;
+const int instace_id = 1;
+const int relay_id = 2;
+
+int
+trg_cb(struct trigger *trigger, void *event)
+{
+	(void)event;
+	bool *check_trg = (bool *)trigger->data;
+	*check_trg = true;
+	return 0;
+}
+
+int
+txn_process_func(va_list ap)
+{
+	bool *check_trg = va_arg(ap, bool *);
+	enum process_type process_type = (enum process_type)va_arg(ap, int);
+	struct txn *txn = txn_begin();
+	txn->fiber = fiber();
+	/* Set the TXN_WAIT_ACK flag to simulate a sync transaction.*/
+	txn_set_flag(txn, TXN_WAIT_ACK);
+	/*
+	 * The true way to push the transaction to limbo is to call
+	 * txn_commit() for sync transaction. But, if txn_commit()
+	 * will be called now, the transaction will not be pushed to
+	 * the limbo because this is the case txn_commit_nop().
+	 * Instead, we push the transaction to the limbo manually
+	 * and call txn_commit (or another) later.
+	 */
+	struct txn_limbo_entry *entry = txn_limbo_append(&txn_limbo,
+							 instace_id, txn);
+	/*
+	 * The trigger is used to verify that the transaction has been
+	 * completed.
+	 */
+	struct trigger trg;
+	trigger_create(&trg, trg_cb, check_trg, NULL);
+
+	switch (process_type) {
+	case TXN_PROCESS_COMMIT:
+		txn_on_commit(txn, &trg);
+		break;
+	case TXN_PROCESS_ROLLBACK:
+		txn_on_rollback(txn, &trg);
+		break;
+	case TXN_PROCESS_TIMEOUT:
+		break;
+	default:
+		unreachable();
+	}
+
+	txn_limbo_assign_lsn(&txn_limbo, entry, fake_lsn);
+	txn_limbo_wait_complete(&txn_limbo, entry);
+
+	switch (process_type) {
+	case TXN_PROCESS_COMMIT:
+		txn_commit(txn);
+		break;
+	case TXN_PROCESS_ROLLBACK:
+		txn_rollback(txn);
+		break;
+	case TXN_PROCESS_TIMEOUT:
+		fiber_yield();
+		break;
+	default:
+		unreachable();
+	}
+	return 0;
+}
+
+int
+txn_confirm_func(va_list ap)
+{
+	/*
+	 * We shouldn't react on gc_wait_cleanup() yield
+	 * inside gc_checkpoint().
+	 */
+	fiber_sleep(0);
+	txn_limbo_ack(&txn_limbo, relay_id, fake_lsn);
+	return 0;
+}
+
+
+void
+test_snap_delay_common(enum process_type process_type)
+{
+	plan(1);
+
+	/*
+	 * We need to clear the limbo vclock before the new test
+	 * variation because the same fake lsn will be used.
+	 */
+	vclock_clear(&txn_limbo.vclock);
+	vclock_create(&txn_limbo.vclock);
+
+	bool check_trg = false;
+	struct fiber *txn_fiber = fiber_new("txn_fiber", txn_process_func);
+	fiber_start(txn_fiber, &check_trg, process_type);
+
+	struct fiber *confirm_entry = fiber_new("confirm_fiber",
+						txn_confirm_func);
+	fiber_wakeup(confirm_entry);
+
+	switch (process_type) {
+	case TXN_PROCESS_COMMIT:
+		ok(gc_checkpoint() == 0 && check_trg,
+		   "check snapshot delay confirm");
+		break;
+	case TXN_PROCESS_ROLLBACK:
+		ok(gc_checkpoint() == -1 && check_trg,
+		   "check snapshot delay rollback");
+		break;
+	case TXN_PROCESS_TIMEOUT:
+		ok(gc_checkpoint() == -1, "check snapshot delay timeout");
+		/* join the "hung" fiber */
+		fiber_set_joinable(txn_fiber, true);
+		fiber_cancel(txn_fiber);
+		fiber_join(txn_fiber);
+		break;
+	default:
+		unreachable();
+	}
+	check_plan();
+}
+
+void
+test_snap_delay_timeout()
+{
+	/* Set the timeout to a small value for the test. */
+	replication_synchro_timeout = 0.01;
+	test_snap_delay_common(TXN_PROCESS_TIMEOUT);
+}
+
+int
+test_snap_delay(va_list ap)
+{
+	header();
+	plan(3);
+	(void)ap;
+	replication_synchro_quorum = 2;
+
+	test_snap_delay_common(TXN_PROCESS_COMMIT);
+	test_snap_delay_common(TXN_PROCESS_ROLLBACK);
+	test_snap_delay_timeout();
+
+	ev_break(loop(), EVBREAK_ALL);
+	footer();
+	test_result = check_plan();
+	return 0;
+}
+} /* end of anonymous namespace */
+
+int
+main(void)
+{
+	memory_init();
+	fiber_init(fiber_c_invoke);
+	gc_init();
+	txn_limbo_init();
+
+	struct fiber *main_fiber = fiber_new("main", test_snap_delay);
+	assert(main_fiber != NULL);
+	fiber_wakeup(main_fiber);
+	ev_run(loop(), 0);
+
+	gc_free();
+	fiber_free();
+	memory_free();
+	return test_result;
+}
diff --git a/test/unit/snap_quorum_delay.result b/test/unit/snap_quorum_delay.result
new file mode 100644
index 000000000..6ca213391
--- /dev/null
+++ b/test/unit/snap_quorum_delay.result
@@ -0,0 +1,12 @@
+	*** test_snap_delay ***
+1..3
+    1..1
+    ok 1 - check snapshot delay confirm
+ok 1 - subtests
+    1..1
+    ok 1 - check snapshot delay rollback
+ok 2 - subtests
+    1..1
+    ok 1 - check snapshot delay timeout
+ok 3 - subtests
+	*** test_snap_delay: done ***
-- 
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