Add examples

Author: xuniq

doc/reference/reference_lua/box_info/synchro.rst

@@ -20,17 +20,18 @@ box.info.synchro
     *   ``queue``:
 
         -   ``owner`` -- ID of the replica that owns the synchronous transaction queue.
-            Once the owner instance appears, all other instances become read-only.
+            Once an owner instance appears, all other instances become read-only.
             If the ``owner`` field is ``0``, then every instance is writeable,
-            but it can't create any synchronous transactions.
-            To claim or re-claim the queue, use :ref:`box.ctl.promote() <box_ctl-promote>` on the instance that you want
+            but they can't create any synchronous transactions.
+            To claim or reclaim the queue, use :ref:`box.ctl.promote() <box_ctl-promote>` on the instance that you want
             to promote.
+            With elections enabled, the instance runs ``box.ctl.promote()`` automatically after winning the elections.
             Since version :doc:`2.10.0 </release/2.10.0>`.
 
         -   ``term`` -- current queue term.
             It contains the term of the last ``PROMOTE``.
             Usually it is equal to :ref:`box.info.election.term <box_info_election>`.
-            However, the queue term value may be less than the corresponding one in election term.
+            However, the queue term value may be less than the corresponding one in the election term.
             It can happen when a new round of elections started, but no one has promoted yet.
             Since version :doc:`2.10.0 </release/2.10.0>`.
 
@@ -45,13 +46,97 @@ box.info.synchro
         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:**
+    **Example 1:**
+
+    In this example, the ``quorum`` field is equal to ``1``.
+    This means that the synchronous transactions work like asynchronous.
+    `1` means that successful WAL write to the master is enough to commit.
 
     ..  code-block:: tarantoolsession
 
         tarantool> box.info.synchro
         ---
         - queue:
+            owner: 1
+            term: 2
             len: 0
+            busy: false
           quorum: 1
+        ...
+
+    **Example 2:**
+
+    First, set a quorum number and a timeout for synchronous replication using the following command:
+
+    ..  code-block:: tarantoolsession
+
+        tarantool> box.cfg{
+                 > replication_synchro_quorum=2,
+                 > replication_synchro_timeout=1000
+                 > }
+
+    Next, check the current state of synchronous replication:
+
+    ..  code-block:: tarantoolsession
+
+        tarantool> box.info.synchro
+        ---
+        - queue:
+            owner: 1
+            term: 2
+            len: 0
+            busy: false
+          quorum: 2
+        ...
+
+    Create a space called ``sync`` and enable synchronous replication on this space.
+    Then, create an index.
+
+    ..  code-block:: tarantoolsession
+
+        tarantool> s = box.schema.space.create("sync", {is_sync=true})
+        tarantool> _ = s:create_index('pk')
+
+    After that, use ``box.ctl.promote`` function to claim the queue:
+
+    ..  code-block:: tarantoolsession
+
+        tarantool> box.ctl.promote()
+
+    Next, use the ``replace`` command:
+
+    ..  code-block:: tarantoolsession
+
+        tarantool> require('fiber').new(function() box.space.sync:replace{1} end)
+        ---
+        - status: suspended
+          name: lua
+          id: 119
+        ...
+        tarantool> require('fiber').new(function() box.space.sync:replace{1} end)
+        ---
+        - status: suspended
+          name: lua
+          id: 120
+        ...
+        tarantool> require('fiber').new(function() box.space.sync:replace{1} end)
+        ---
+        - status: suspended
+          name: lua
+          id: 121
+        ...
+
+    If you use the ``box.info.synchro`` command again,
+    you will see that now there are 3 transactions waiting in the queue:
+
+    ..  code-block:: tarantoolsession
+
+        tarantool> box.info.synchro
+        ---
+        - queue:
+            owner: 1
+            term: 2
+            len: 3
+            busy: false
+          quorum: 2
         ...