Update box.info.synchro

Author: xuniq

doc/reference/reference_lua/box_info.rst

@@ -92,6 +92,10 @@ Below is a list of all ``box.info`` functions.
            - Show the current state of a replica set node
              in regards to leader election
 
+        *  - :doc:`./box_info/synchro`
+           - Show the current state of synchronous replication
+
+
 ..  toctree::
     :hidden:
 
@@ -102,3 +106,4 @@ Below is a list of all ``box.info`` functions.
     box_info/replication
     box_info/listen
     box_info/election
+    box_info/synchro

doc/reference/reference_lua/box_info/synchro.rst

@@ -0,0 +1,38 @@
+..  _box_info_synchro:
+
+================================================================================
+box.info.synchro
+================================================================================
+
+..  module:: box.info
+
+..  data:: synchro
+
+    Since version :doc:`2.8.1 </release/2.8.1>`.
+    Show the current state of synchronous replication.
+
+    In :ref:`synchronous replication <repl_sync>`, a transaction is considered committed only after achieving
+    the required quorum number.
+    While the commit responses from remote nodes are being collected, the data is waiting in the queue.
+
+    The following information is provided:
+
+    *   ``queue``:
+
+        -   ``len`` -- current number of entries that are waiting in the queue.
+
+    *   ``quorum`` -- evaluated value of the
+        :ref:`replication_synchro_quorum <cfg_replication-replication_synchro_quorum>` configuration option.
+        Since version :doc:`2.5.3 </release/2.5.3>`, the option can be set as a dynamic formula.
+        In this case, the value in the ``quorum`` member depends on the current number of replicas.
+
+    **Example:**
+
+    ..  code-block:: tarantoolsession
+
+        tarantool> box.info.synchro
+        ---
+        - queue:
+            len: 0
+          quorum: 1
+        ...