log switchover duration in db

model/lantern/lantern_resource.rb

@@ -236,6 +236,25 @@ def delete_logical_subscription(name)
     representative_server.run_query_all("DROP SUBSCRIPTION IF EXISTS #{name}")
   end
 
+  def mark_switchover_start
+    commands = <<SQL
+   BEGIN;
+   DROP TABLE IF EXISTS _ldb_switchover_info;
+   CREATE TABLE _ldb_switchover_info(
+     id SERIAL PRIMARY KEY,
+     started_at TIMESTAMP NOT NULL DEFAULT NOW(),
+     finished_at TIMESTAMP
+   );
+   INSERT INTO _ldb_switchover_info(started_at) VALUES (NOW());
+   COMMIT;
+SQL
+    representative_server.run_query(commands)
+  end
+
+  def mark_switchover_finish
+    representative_server.run_query("UPDATE _ldb_switchover_info SET finished_at=NOW()")
+  end
+
   def create_logical_replica(lantern_version: nil, extras_version: nil, minor_version: nil, pg_upgrade: nil)
     # TODO::
     # 1. If new database will be created during logical replication it won't be added automatically

prog/lantern/lantern_resource_nexus.rb

@@ -267,6 +267,8 @@ def before_run
     # remove ddl_log
     lantern_resource.drop_ddl_log
 
+    lantern_resource.mark_switchover_finish
+
     hop_wait
   end
 
@@ -336,6 +338,7 @@ def before_run
   label def switchover_with_parent
     decr_switchover_with_parent
     lantern_resource.parent.set_to_readonly
+    lantern_resource.mark_switchover_start
     hop_wait_for_synchronization
   end
 

spec/model/lantern/lantern_resource_spec.rb

@@ -375,4 +375,22 @@
       expect { lantern_resource.rollback_switchover }.not_to raise_error
     end
   end
+
+  describe "#mark_switchover_start" do
+    it "marks switchover start time" do
+      representative_server = instance_double(LanternServer)
+      expect(lantern_resource).to receive(:representative_server).and_return(representative_server).at_least(:once)
+      expect(lantern_resource.representative_server).to receive(:run_query).with(a_string_matching(/_ldb_switchover_info/))
+      expect { lantern_resource.mark_switchover_start }.not_to raise_error
+    end
+  end
+
+  describe "#mark_switchover_finish" do
+    it "marks switchover finish time" do
+      representative_server = instance_double(LanternServer)
+      expect(lantern_resource).to receive(:representative_server).and_return(representative_server).at_least(:once)
+      expect(lantern_resource.representative_server).to receive(:run_query).with(a_string_matching(/_ldb_switchover_info/))
+      expect { lantern_resource.mark_switchover_finish }.not_to raise_error
+    end
+  end
 end

spec/prog/lantern/lantern_resource_nexus_spec.rb

@@ -440,6 +440,7 @@
       expect(lantern_resource).to receive(:update).with(parent_id: nil)
       expect(lantern_resource).to receive(:timeline).and_return(timeline)
       expect(lantern_resource).to receive(:drop_ddl_log)
+      expect(lantern_resource).to receive(:mark_switchover_finish)
       expect(timeline).to receive(:update).with(parent_id: nil)
 
       expect { nx.finish_take_over }.to hop("wait")
@@ -450,6 +451,7 @@
     it "sets parent to readonly and hop" do
       parent = instance_double(LanternResource)
       expect(lantern_resource).to receive(:parent).and_return(parent)
+      expect(lantern_resource).to receive(:mark_switchover_start)
       expect(parent).to receive(:set_to_readonly)
       expect(nx).to receive(:decr_switchover_with_parent)