[Tarantool-patches] [PATCH v7 4/8] qsync: direct write of CONFIRM/ROLLBACK into a journal

[Cyrill Gorcunov]

When we need to write CONFIRM or ROLLBACK message (which is
a binary record in msgpack format) into a journal we use txn code
to allocate a new transaction, encode there a message and pass it
to walk the long txn path before it hit the journal. This is not
only resource wasting but also somehow strange from architectural
point of view.

Instead lets encode a record on the stack and write it to the journal
directly.

Part-of #5129

Signed-off-by: Cyrill Gorcunov <gorcunov at gmail.com>
---
 src/box/txn_limbo.c | 64 ++++++++++++++++++++++-----------------------
 1 file changed, 32 insertions(+), 32 deletions(-)

diff --git a/src/box/txn_limbo.c b/src/box/txn_limbo.c
index ed8c10419..447630d23 100644
--- a/src/box/txn_limbo.c
+++ b/src/box/txn_limbo.c
@@ -32,6 +32,7 @@
 #include "txn_limbo.h"
 #include "replication.h"
 #include "iproto_constants.h"
+#include "journal.h"
 
 struct txn_limbo txn_limbo;
 
@@ -272,6 +273,17 @@ txn_limbo_wait_complete(struct txn_limbo *limbo, struct txn_limbo_entry *entry)
 	return 0;
 }
 
+/**
+ * A callback for synchronous write: txn_limbo_write_synchro fiber
+ * waiting to proceed once a record is written to WAL.
+ */
+static void
+txn_limbo_write_cb(struct journal_entry *entry)
+{
+	assert(entry->complete_data != NULL);
+	fiber_wakeup(entry->complete_data);
+}
+
 static void
 txn_limbo_write_synchro(struct txn_limbo *limbo, uint32_t type, int64_t lsn)
 {
@@ -284,46 +296,34 @@ txn_limbo_write_synchro(struct txn_limbo *limbo, uint32_t type, int64_t lsn)
 
 	/*
 	 * This is a synchronous commit so we can
-	 * use body and row allocated on a stack.
+	 * allocate everything on a stack.
 	 */
 	struct synchro_body_bin body;
 	struct xrow_header row;
-	struct request request = {
-		.header = &row,
-	};
+	char buf[sizeof(struct journal_entry) +
+		 sizeof(struct xrow_header *)];
 
-	struct txn *txn = txn_begin();
-	if (txn == NULL)
-		goto rollback;
+	struct journal_entry *entry = (struct journal_entry *)buf;
+	entry->rows[0] = &row;
 
 	xrow_encode_synchro(&row, &body, &req);
 
-	/*
-	 * This is not really a transaction. It just uses txn API
-	 * to put the data into WAL. And obviously it should not
-	 * go to the limbo and block on the very same sync
-	 * transaction which it tries to confirm now.
-	 */
-	txn_set_flag(txn, TXN_FORCE_ASYNC);
-
-	if (txn_begin_stmt(txn, NULL) != 0)
-		goto rollback;
-	if (txn_commit_stmt(txn, &request) != 0)
-		goto rollback;
-	if (txn_commit(txn) != 0)
-		goto rollback;
-	return;
+	journal_entry_create(entry, 1, xrow_approx_len(&row),
+			     txn_limbo_write_cb, fiber());
 
-rollback:
-	/*
-	 * XXX: the stub is supposed to be removed once it is defined what to do
-	 * when a synchro request WAL write fails. One of the possible
-	 * solutions: log the error, keep the limbo queue as is and probably put
-	 * in rollback mode. Then provide a hook to call manually when WAL
-	 * problems are fixed. Or retry automatically with some period.
-	 */
-	panic("Could not write a synchro request to WAL: lsn = %lld, type = "
-	      "%s\n", lsn, iproto_type_name(type));
+	if (journal_write(entry) != 0 || entry->res < 0) {
+		diag_set(ClientError, ER_WAL_IO);
+		diag_log();
+		/*
+		 * XXX: the stub is supposed to be removed once it is defined what to do
+		 * when a synchro request WAL write fails. One of the possible
+		 * solutions: log the error, keep the limbo queue as is and probably put
+		 * in rollback mode. Then provide a hook to call manually when WAL
+		 * problems are fixed. Or retry automatically with some period.
+		 */
+		panic("Could not write a synchro request to WAL: lsn = %lld, type = "
+		      "%s\n", lsn, type == IPROTO_CONFIRM ? "CONFIRM" : "ROLLBACK");
+	}
 }
 
 /**
-- 
2.26.2