fix: remove unique index on peer_address

The `peer_address` parameter is an inbound address used for
communication with the peer. It shouldn't be confused with the listen
address. The persisted `peer_address` may become obsolete due to
circumstances beyond picodata control (e.g. DNS or IP changes). Thus
there's no point in its prior validation, including the uniqueness
check.

There's also no such task as getting peer by peer_address.

To sum up, an index over `peer_address` is useless. It only creates
problems and causes panics.

Close https://git.picodata.io/picodata/picodata/picodata/-/issues/88

src/traft/mod.rs

@@ -65,8 +65,14 @@ pub enum Op {
 /// Serializable struct representing a member of the raft group.
 #[derive(Clone, Debug, Default, Serialize, Deserialize, PartialEq)]
 pub struct Peer {
+    /// Used for identifying raft nodes.
+    /// Must be unique in the raft group.
     pub raft_id: u64,
+    /// Inbound address used for communication with the node.
+    /// Not to be confused with listen address.
     pub peer_address: String,
+    /// Reflects the role of the node in the raft group.
+    /// Non-voters are also called learners in terms of raft.
     pub voter: bool,
     pub instance_id: String,
     pub replicaset_id: String,

src/traft/storage.rs

@@ -97,11 +97,6 @@ impl Storage {
                 parts = {{'replicaset_id'}, {'commit_index'}},
                 unique = false,
             })
-            box.space.raft_group:create_index('peer_address', {
-                if_not_exists = true,
-                parts = {{'peer_address'}},
-                unique = true,
-            })
         "#,
         );
     }
@@ -558,24 +553,19 @@ inventory::submit!(crate::InnerTest {
             )
         );
 
-        assert_err!(
-            Storage::persist_peer(&traft::Peer {
-                raft_id: 99,
-                peer_address: "addr:1".into(),
+        {
+            // Ensure traft storage doesn't impose restrictions
+            // on peer_address uniqueness.
+            let peer = |id: u64, addr: &str| traft::Peer {
+                raft_id: id,
+                instance_id: format!("i{id}"),
+                peer_address: addr.into(),
                 ..Default::default()
-            }),
-            concat!(
-                "unknown error",
-                " Tarantool error:",
-                " TupleFound: Duplicate key exists",
-                " in unique index \"peer_address\"",
-                " in space \"raft_group\"",
-                " with old tuple",
-                " - [1, \"addr:1\", true, \"i1\", \"r1\", \"i1-uuid\", \"r1-uuid\", 1]",
-                " and new tuple",
-                " - [99, \"addr:1\", false, \"\", \"\", \"\", \"\", 0]"
-            )
-        );
+            };
+
+            Storage::persist_peer(&peer(10, "addr:collision")).unwrap();
+            Storage::persist_peer(&peer(11, "addr:collision")).unwrap();
+        }
 
         let peer_by_raft_id = |id: u64| Storage::peer_by_raft_id(id).unwrap().unwrap();
         {
@@ -594,6 +584,10 @@ inventory::submit!(crate::InnerTest {
             assert_eq!(peer_by_instance_id("i3").peer_address, "addr:3");
             assert_eq!(peer_by_instance_id("i4").peer_address, "addr:4");
             assert_eq!(peer_by_instance_id("i5").peer_address, "addr:5");
+            assert_eq!(
+                peer_by_instance_id("i10").peer_address,
+                peer_by_instance_id("i11").peer_address
+            );
             assert_eq!(Storage::peer_by_instance_id("i6"), Ok(None));
         }
 
@@ -642,7 +636,6 @@ inventory::submit!(crate::InnerTest {
             )
         );
 
-        raft_group.index("peer_address").unwrap().drop().unwrap();
         raft_group.primary_key().drop().unwrap();
 
         assert_err!(