[Tarantool-patches] [PATCH 3/8] txn: add TXN_WAIT_ACK flag

[Serge Petrenko]

From: Vladislav Shpilevoy <v.shpilevoy at tarantool.org>

When a transaction touches a synchronous space, its commit
procedure changes. The transaction enters state of 'waiting for
acks' from replicas and from own master's WAL.

To denote the state there is a new transaction flag -
TXN_WAIT_ACK.

Part of #4844
---
 src/box/txn.c | 17 +++++++++++++++--
 src/box/txn.h |  7 +++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/box/txn.c b/src/box/txn.c
index 123520166..60870f536 100644
--- a/src/box/txn.c
+++ b/src/box/txn.c
@@ -495,24 +495,37 @@ txn_journal_entry_new(struct txn *txn)
 
 	struct xrow_header **remote_row = req->rows;
 	struct xrow_header **local_row = req->rows + txn->n_applier_rows;
+	bool is_sync = false;
+	/*
+	 * Only local transactions, originated from the master,
+	 * can enter 'waiting for acks' state. It means, only
+	 * author of the transaction can collect acks. Replicas
+	 * consider it a normal async transaction so far.
+	 */
+	bool is_local = true;
 
 	stailq_foreach_entry(stmt, &txn->stmts, next) {
 		if (stmt->has_triggers) {
 			txn_init_triggers(txn);
 			rlist_splice(&txn->on_commit, &stmt->on_commit);
 		}
+		is_sync = is_sync || stmt->space->def->opts.is_sync;
 
 		/* A read (e.g. select) request */
 		if (stmt->row == NULL)
 			continue;
 
-		if (stmt->row->replica_id == 0)
+		if (stmt->row->replica_id == 0) {
 			*local_row++ = stmt->row;
-		else
+		} else {
 			*remote_row++ = stmt->row;
+			is_local = false;
+		}
 
 		req->approx_len += xrow_approx_len(stmt->row);
 	}
+	if (is_sync && is_local)
+		txn_set_flag(txn, TXN_WAIT_ACK);
 
 	assert(remote_row == req->rows + txn->n_applier_rows);
 	assert(local_row == remote_row + txn->n_new_rows);
diff --git a/src/box/txn.h b/src/box/txn.h
index 3f6d79d5c..232cc07a8 100644
--- a/src/box/txn.h
+++ b/src/box/txn.h
@@ -66,6 +66,13 @@ enum txn_flag {
 	TXN_CAN_YIELD,
 	/** on_commit and/or on_rollback list is not empty. */
 	TXN_HAS_TRIGGERS,
+	/**
+	 * Transaction, touched sync spaces, enters 'waiting for
+	 * acks' state before commit. In this state it waits until
+	 * it is replicated onto a quorum of replicas, and only
+	 * then finishes commit and returns success to a user.
+	 */
+	TXN_WAIT_ACK,
 };
 
 enum {
-- 
2.24.3 (Apple Git-128)