diff --git a/apps/state/lib/state/server.ex b/apps/state/lib/state/server.ex
index 3dd43aa80..91ba242d7 100644
--- a/apps/state/lib/state/server.ex
+++ b/apps/state/lib/state/server.ex
@@ -187,9 +187,6 @@ defmodule State.Server do
       @impl State.Server
       def post_load_hook(structs), do: structs
 
-      @impl State.Server
-      def pre_insert_hook(item), do: [item]
-
       @impl Events.Server
       def handle_event({:fetch, unquote(opts[:fetched_filename])}, body, _, state) do
         case handle_call({:new_state, body}, nil, state) do
@@ -227,7 +224,6 @@ defmodule State.Server do
                      new_state: 2,
                      post_commit_hook: 0,
                      post_load_hook: 1,
-                     pre_insert_hook: 1,
                      select: 1,
                      select: 2,
                      select_limit: 2,
@@ -307,8 +303,8 @@ defmodule State.Server do
     recordable = module.recordable()
     indices = module.indices()
     attributes = recordable.fields()
-    id_field = List.first(attributes)
-    index = Enum.reject(indices, &Kernel.==(&1, id_field))
+    key_index = module.key_index()
+    index = Enum.reject(indices, &Kernel.==(&1, key_index))
     recreate_table(module, attributes: attributes, index: index, record_name: recordable)
   end
 
@@ -345,28 +341,47 @@ defmodule State.Server do
       )
 
     if enum do
-      with {:atomic, :ok} <- :mnesia.transaction(&create_children/2, [enum, module], 0) do
-        :ok
+      has_hook? = function_exported?(module, :pre_insert_hook, 1)
+
+      update =
+        case enum do
+          {:partial, enum} when has_hook? ->
+            {:partial, Stream.flat_map(enum, &module.pre_insert_hook/1)}
+
+          {:partial, _enum} = update ->
+            update
+
+          enum when has_hook? ->
+            {:all, Stream.flat_map(enum, &module.pre_insert_hook/1)}
+
+          enum ->
+            {:all, enum}
+        end
+
+      with {:atomic, count} <-
+             :mnesia.transaction(&create_children/2, [update, module], 10) do
+        {:ok, count}
       end
     else
-      :ok
+      {:ok, 0}
     end
   end
 
-  defp create_children(enum, module) do
+  defp create_children({:all, enum}, module) do
+    recordable = module.recordable()
     :mnesia.write_lock_table(module)
 
     delete_all = fn ->
       all_keys = :mnesia.all_keys(module)
+
       :lists.foreach(&:mnesia.delete(module, &1, :write), all_keys)
     end
 
     write_new = fn ->
-      recordable = module.recordable()
-
-      enum
-      |> Stream.flat_map(&module.pre_insert_hook/1)
-      |> Enum.each(&:mnesia.write(module, recordable.to_record(&1), :write))
+      Enum.reduce(enum, 0, fn item, count ->
+        :mnesia.write(module, recordable.to_record(item), :write)
+        count + 1
+      end)
     end
 
     :ok =
@@ -377,13 +392,40 @@ defmodule State.Server do
         end
       )
 
-    :ok =
+    count =
       debug_time(
         write_new,
         fn milliseconds ->
           "write_new #{module} #{inspect(self())} took #{milliseconds}ms"
         end
       )
+
+    count
+  end
+
+  defp create_children({:partial, enum}, module) do
+    recordable = module.recordable()
+    key_index = module.key_index()
+
+    update = fn ->
+      enum
+      |> Enum.group_by(&Map.get(&1, key_index))
+      |> Enum.reduce(0, fn {key, items}, count ->
+        :mnesia.delete(module, key, :write)
+        :lists.foreach(&:mnesia.write(module, recordable.to_record(&1), :write), items)
+        length(items) + count
+      end)
+    end
+
+    count =
+      debug_time(
+        update,
+        fn milliseconds ->
+          "partial_update #{module} #{inspect(self())} took #{milliseconds}ms"
+        end
+      )
+
+    count
   end
 
   def size(module) do
@@ -481,7 +523,7 @@ defmodule State.Server do
     recordable = module.recordable()
 
     records
-    |> Enum.map(&recordable.from_record(&1))
+    |> Enum.map(&recordable.from_record/1)
     |> module.post_load_hook()
     |> State.all(opts)
   end
@@ -524,7 +566,7 @@ defmodule State.Server do
   end
 
   defp do_handle_new_state(module, func) do
-    :ok =
+    {:ok, update_count} =
       debug_time(
         fn -> create!(func, module) end,
         fn milliseconds ->
@@ -542,15 +584,13 @@ defmodule State.Server do
         end
       )
 
-    new_size = module.size()
-
     _ =
       Logger.info(fn ->
-        "Update #{module} #{inspect(self())}: #{new_size} items"
+        "Update #{module} #{inspect(self())}: #{update_count} items"
       end)
 
     module.update_metadata()
-    Events.publish({:new_state, module}, new_size)
+    Events.publish({:new_state, module}, update_count)
 
     :ok
   end
diff --git a/apps/state/test/state/vehicle_test.exs b/apps/state/test/state/vehicle_test.exs
index ab4ef1c01..3f867573f 100644
--- a/apps/state/test/state/vehicle_test.exs
+++ b/apps/state/test/state/vehicle_test.exs
@@ -88,6 +88,23 @@ defmodule State.VehicleTest do
     assert [_, _] = all()
   end
 
+  test "it can accept a partial update which only modifies some vehicles" do
+    new_state([
+      %Vehicle{id: "one", trip_id: "1", route_id: "1"},
+      %Vehicle{id: "two", trip_id: "2", route_id: "1"}
+    ])
+
+    new_state(
+      {:partial,
+       [
+         %Vehicle{id: "one", trip_id: "3", route_id: "1"}
+       ]}
+    )
+
+    assert %Vehicle{id: "one", trip_id: "3"} = by_id("one")
+    assert %Vehicle{id: "two", trip_id: "2"} = by_id("two")
+  end
+
   @tag :capture_log
   test "an invalid state doesn't crash the server" do
     vehicle = %Vehicle{id: "1", trip_id: "2"}