[tarantool-patches] [PATCH v3 08/14] wal: enable asyncronous wal writes

[Georgy Kirichenko <georgy@tarantool.org>]

Allow to send a journal entry to wal without to wait until the writing
was finished. Two methods were introduced:
 * async_write method emits an entry to be written, returns 0 if the
 entry was successfully scheduled;
 * async_wait method waits until writing was finished and returns a
 result of journal write.

Prerequisites: #1254
---
 src/box/box.cc    | 30 ++++++++++++++++++++---
 src/box/journal.c | 21 +++++++++++++++-
 src/box/journal.h | 30 +++++++++++++++++++++++
 src/box/wal.c     | 62 +++++++++++++++++++++++++++++++++++++++++------
 4 files changed, 130 insertions(+), 13 deletions(-)

diff --git a/src/box/box.cc b/src/box/box.cc
index a88e762c0..d0616095b 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -308,19 +308,41 @@ struct recovery_journal {
  * min/max LSN of created LSM levels.
  */
 static int64_t
-recovery_journal_write(struct journal *base,
-		       struct journal_entry *entry)
+recovery_journal_async_write(struct journal *base,
+			     struct journal_entry *entry)
 {
 	struct recovery_journal *journal = (struct recovery_journal *) base;
+	entry->res = vclock_sum(journal->vclock);
 	entry->done = true;
 	fiber_cond_broadcast(&entry->done_cond);
-	return vclock_sum(journal->vclock);
+	return 0;
+}
+
+static int64_t
+recovery_journal_async_wait(struct journal *base,
+			    struct journal_entry *entry)
+{
+	(void) base;
+	assert(entry->done);
+	return entry->res;
+}
+
+static int64_t
+recovery_journal_write(struct journal *base,
+		       struct journal_entry *entry)
+{
+	if (recovery_journal_async_write(base, entry) == 0)
+		return recovery_journal_async_wait(base, entry);
+	return -1;
 }
 
 static inline void
 recovery_journal_create(struct recovery_journal *journal, struct vclock *v)
 {
-	journal_create(&journal->base, recovery_journal_write, NULL);
+	journal_create(&journal->base, recovery_journal_write,
+		       recovery_journal_async_write,
+		       recovery_journal_async_wait,
+		       NULL);
 	journal->vclock = v;
 }
 
diff --git a/src/box/journal.c b/src/box/journal.c
index 6406d6f01..b978e6752 100644
--- a/src/box/journal.c
+++ b/src/box/journal.c
@@ -37,16 +37,35 @@
  * but txn_commit() must work.
  */
 static int64_t
-dummy_journal_write(struct journal *journal, struct journal_entry *entry)
+dummy_async_write(struct journal *journal, struct journal_entry *entry)
 {
 	(void) journal;
+	entry->res = 0;
 	entry->done = true;
 	fiber_cond_broadcast(&entry->done_cond);
 	return 0;
 }
 
+static int64_t
+dummy_async_wait(struct journal *journal, struct journal_entry *entry)
+{
+	(void) journal;
+	assert(entry->done);
+	return entry->res;
+}
+
+static int64_t
+dummy_journal_write(struct journal *journal, struct journal_entry *entry)
+{
+	if (dummy_async_write(journal, entry) == 0)
+		return dummy_async_wait(journal, entry);
+	return -1;
+}
+
 static struct journal dummy_journal = {
 	dummy_journal_write,
+	dummy_async_write,
+	dummy_async_wait,
 	NULL,
 };
 
diff --git a/src/box/journal.h b/src/box/journal.h
index 618c68eb2..e7fe9154a 100644
--- a/src/box/journal.h
+++ b/src/box/journal.h
@@ -95,6 +95,10 @@ journal_entry_new(size_t n_rows, struct region *region);
 struct journal {
 	int64_t (*write)(struct journal *journal,
 			 struct journal_entry *req);
+	int64_t (*async_write)(struct journal *journal,
+			       struct journal_entry *req);
+	int64_t (*async_wait)(struct journal *journal,
+			      struct journal_entry *req);
 	void (*destroy)(struct journal *journal);
 };
 
@@ -116,6 +120,28 @@ journal_write(struct journal_entry *entry)
 	return current_journal->write(current_journal, entry);
 }
 
+/**
+ * Send a single entry to write.
+ *
+ * @return   0 if write was scheduled or -1 on error.
+ */
+static inline int64_t
+journal_async_write(struct journal_entry *entry)
+{
+	return current_journal->async_write(current_journal, entry);
+}
+
+/**
+ * Wait until entry processing finished.
+ * @return   a log sequence number (vclock signature) of the entry
+ *           or -1 on error.
+ */
+static inline int64_t
+journal_async_wait(struct journal_entry *entry)
+{
+	return current_journal->async_wait(current_journal, entry);
+}
+
 /**
  * Change the current implementation of the journaling API.
  * Happens during life cycle of an instance:
@@ -148,9 +174,13 @@ journal_set(struct journal *new_journal)
 static inline void
 journal_create(struct journal *journal,
 	       int64_t (*write)(struct journal *, struct journal_entry *),
+	       int64_t (*async_write)(struct journal *, struct journal_entry *),
+	       int64_t (*async_wait)(struct journal *, struct journal_entry *),
 	       void (*destroy)(struct journal *))
 {
 	journal->write = write;
+	journal->async_write = async_write,
+	journal->async_wait = async_wait,
 	journal->destroy = destroy;
 }
 
diff --git a/src/box/wal.c b/src/box/wal.c
index 5951817d0..86d021896 100644
--- a/src/box/wal.c
+++ b/src/box/wal.c
@@ -63,9 +63,18 @@ int wal_dir_lock = -1;
 static int64_t
 wal_write(struct journal *, struct journal_entry *);
 
+static int64_t
+wal_async_write(struct journal *, struct journal_entry *);
+
+static int64_t
+wal_async_wait(struct journal *, struct journal_entry *);
+
 static int64_t
 wal_write_in_wal_mode_none(struct journal *, struct journal_entry *);
 
+static int64_t
+wal_async_write_in_wal_mode_none(struct journal *, struct journal_entry *);
+
 /*
  * WAL writer - maintain a Write Ahead Log for every change
  * in the data state.
@@ -351,7 +360,10 @@ wal_writer_create(struct wal_writer *writer, enum wal_mode wal_mode,
 	writer->wal_max_rows = wal_max_rows;
 	writer->wal_max_size = wal_max_size;
 	journal_create(&writer->base, wal_mode == WAL_NONE ?
-		       wal_write_in_wal_mode_none : wal_write, NULL);
+		       wal_write_in_wal_mode_none : wal_write,
+		       wal_mode == WAL_NONE ?
+		       wal_async_write_in_wal_mode_none: wal_async_write,
+		       wal_async_wait, NULL);
 
 	struct xlog_opts opts = xlog_opts_default;
 	opts.sync_is_async = true;
@@ -1118,10 +1130,10 @@ wal_writer_f(va_list ap)
 
 /**
  * WAL writer main entry point: queue a single request
- * to be written to disk and wait until this task is completed.
+ * to be written to disk.
  */
-int64_t
-wal_write(struct journal *journal, struct journal_entry *entry)
+static int64_t
+wal_async_write(struct journal *journal, struct journal_entry *entry)
 {
 	struct wal_writer *writer = (struct wal_writer *) journal;
 
@@ -1138,6 +1150,8 @@ wal_write(struct journal *journal, struct journal_entry *entry)
 		say_error("Aborting transaction %llu during "
 			  "cascading rollback",
 			  vclock_sum(&writer->vclock));
+		entry->done = true;
+		fiber_cond_broadcast(&entry->done_cond);
 		return -1;
 	}
 
@@ -1152,6 +1166,8 @@ wal_write(struct journal *journal, struct journal_entry *entry)
 		if (batch == NULL) {
 			diag_set(OutOfMemory, sizeof(struct wal_msg),
 				 "region", "struct wal_msg");
+			entry->done = true;
+			fiber_cond_broadcast(&entry->done_cond);
 			return -1;
 		}
 		wal_msg_create(batch);
@@ -1166,16 +1182,34 @@ wal_write(struct journal *journal, struct journal_entry *entry)
 	batch->approx_len += entry->approx_len;
 	writer->wal_pipe.n_input += entry->n_rows * XROW_IOVMAX;
 	cpipe_flush_input(&writer->wal_pipe);
+	return 0;
+}
 
+static int64_t
+wal_async_wait(struct journal *journal, struct journal_entry *entry)
+{
+	(void) journal;
 	while (!entry->done)
 		fiber_cond_wait(&entry->done_cond);
 
 	return entry->res;
 }
 
-int64_t
-wal_write_in_wal_mode_none(struct journal *journal,
-			   struct journal_entry *entry)
+/**
+ * WAL writer main entry point: queue a single request
+ * to be written to disk and wait until this task is completed.
+ */
+static int64_t
+wal_write(struct journal *journal, struct journal_entry *entry)
+{
+	if (wal_async_write(journal, entry) != 0)
+		return -1;
+	return wal_async_wait(journal, entry);
+}
+
+static int64_t
+wal_async_write_in_wal_mode_none(struct journal *journal,
+				 struct journal_entry *entry)
 {
 	struct wal_writer *writer = (struct wal_writer *) journal;
 	struct vclock vclock_diff;
@@ -1184,7 +1218,19 @@ wal_write_in_wal_mode_none(struct journal *journal,
 		       entry->rows + entry->n_rows);
 	vclock_merge(&writer->vclock, &vclock_diff);
 	vclock_copy(&replicaset.vclock, &writer->vclock);
-	return vclock_sum(&writer->vclock);
+	entry->res = vclock_sum(&writer->vclock);
+	entry->done = true;
+	fiber_cond_broadcast(&entry->done_cond);
+	return 0;
+}
+
+static int64_t
+wal_write_in_wal_mode_none(struct journal *journal,
+			   struct journal_entry *entry)
+{
+	if (wal_async_write_in_wal_mode_none(journal, entry) != 0)
+		return -1;
+	return wal_async_wait(journal, entry);
 }
 
 void
-- 
2.21.0