diff --git a/lib/ecto/repo.ex b/lib/ecto/repo.ex
index 91b6398b45..8af8e3014e 100644
--- a/lib/ecto/repo.ex
+++ b/lib/ecto/repo.ex
@@ -1675,6 +1675,11 @@ defmodule Ecto.Repo do
       `{:unsafe_fragment, "(coalesce(firstname, ''), coalesce(lastname, '')) WHERE middlename IS NULL"}` for
       `ON CONFLICT (coalesce(firstname, ''), coalesce(lastname, '')) WHERE middlename IS NULL` SQL query.
 
+    * `:replace_changed` - Whether to include `:conflict_target` fields when `:on_conflict`
+      is `:replace_all` or `{:replace_all_except, fields}`. If `true`, the conflict target
+      fields are not updated in order to enable optimizations such as HOT updates in PostgreSQL.
+      Defaults to `true`.
+
     * `:placeholders` - A map with placeholders. This feature is not supported
       by all databases. See the ["Placeholders" section](#c:insert_all/3-placeholders) for more information.
 
@@ -1718,7 +1723,9 @@ defmodule Ecto.Repo do
       such as IDs and autogenerated timestamps (`inserted_at` and `updated_at`).
       Do not use this option if you have auto-incrementing primary keys, as they
       will also be replaced. You most likely want to use `{:replace_all_except, [:id]}`
-      or `{:replace, fields}` explicitly instead. This option requires a schema
+      or `{:replace, fields}` explicitly instead. This option requires a schema. Fields
+      specified by `:conflict_target` will be ignored unless `:replace_changed` is
+      configured to be `false`
 
     * `{:replace_all_except, fields}` - same as above except the given fields
       (and the ones given as conflict target) are not replaced. This option
@@ -1842,6 +1849,11 @@ defmodule Ecto.Repo do
       `{:unsafe_fragment, "(coalesce(firstname, ""), coalesce(lastname, "")) WHERE middlename IS NULL"}` for
       `ON CONFLICT (coalesce(firstname, ""), coalesce(lastname, "")) WHERE middlename IS NULL` SQL query.
 
+    * `:replace_changed` - Whether to include `:conflict_target` fields when `:on_conflict`
+      is `:replace_all` or `{:replace_all_except, fields}`. If `true`, the conflict fields
+      are not updated in order to enable optimizations such as HOT updates in PostgreSQL.
+      Defaults to `true`.
+
     * `:stale_error_field` - The field where stale errors will be added in
       the returning changeset. This option can be used to avoid raising
       `Ecto.StaleEntryError`.
@@ -1880,7 +1892,9 @@ defmodule Ecto.Repo do
       such as IDs and autogenerated timestamps (`inserted_at` and `updated_at`).
       Do not use this option if you have auto-incrementing primary keys, as they
       will also be replaced. You most likely want to use `{:replace_all_except, [:id]}`
-      or `{:replace, fields}` explicitly instead. This option requires a schema
+      or `{:replace, fields}` explicitly instead. This option requires a schema.  Fields
+      specified by `:conflict_target` will be ignored unless `:replace_changed` is
+      configured to be `false`
 
     * `{:replace_all_except, fields}` - same as above except the given fields are
       not replaced. This option requires a schema
diff --git a/lib/ecto/repo/schema.ex b/lib/ecto/repo/schema.ex
index e2fedf5f60..f0ba97a715 100644
--- a/lib/ecto/repo/schema.ex
+++ b/lib/ecto/repo/schema.ex
@@ -69,9 +69,10 @@ defmodule Ecto.Repo.Schema do
     on_conflict = Keyword.get(opts, :on_conflict, :raise)
     conflict_target = Keyword.get(opts, :conflict_target, [])
     conflict_target = conflict_target(conflict_target, dumper)
+    replace_changed? = Keyword.get(opts, :replace_changed, true)
 
     {on_conflict, conflict_cast_params} =
-      on_conflict(on_conflict, conflict_target, schema_meta, counter, dumper, adapter)
+      on_conflict(on_conflict, conflict_target, replace_changed?, schema_meta, counter, dumper, adapter)
 
     opts =
       Keyword.put(
@@ -445,6 +446,7 @@ defmodule Ecto.Repo.Schema do
     on_conflict = Keyword.get(opts, :on_conflict, :raise)
     conflict_target = Keyword.get(opts, :conflict_target, [])
     conflict_target = conflict_target(conflict_target, dumper)
+    replace_changed? = Keyword.get(opts, :replace_changed, true)
 
     # On insert, we always merge the whole struct into the
     # changeset as changes, except the primary key if it is nil.
@@ -479,6 +481,7 @@ defmodule Ecto.Repo.Schema do
           on_conflict(
             on_conflict,
             conflict_target,
+            replace_changed?,
             schema_meta,
             fn -> length(dump_changes) end,
             dumper,
@@ -889,7 +892,7 @@ defmodule Ecto.Repo.Schema do
     end
   end
 
-  defp on_conflict(on_conflict, conflict_target, schema_meta, counter_fun, dumper, adapter) do
+  defp on_conflict(on_conflict, conflict_target, replace_changed?, schema_meta, counter_fun, dumper, adapter) do
     %{source: source, schema: schema, prefix: prefix} = schema_meta
 
     case on_conflict do
@@ -913,7 +916,7 @@ defmodule Ecto.Repo.Schema do
         # Remove the conflict targets from the replacing fields
         # since the values don't change and this allows postgres to
         # possibly perform a HOT optimization: https://www.postgresql.org/docs/current/storage-hot.html
-        to_remove = List.wrap(conflict_target)
+        to_remove = if replace_changed?, do: List.wrap(conflict_target), else: []
         replace = replace_all_fields!(:replace_all, schema, to_remove)
 
         if replace == [], do: raise(ArgumentError, "empty list of fields to update, use the `:replace` option instead")
@@ -921,7 +924,7 @@ defmodule Ecto.Repo.Schema do
         {{replace, [], conflict_target}, []}
 
       {:replace_all_except, fields} ->
-        to_remove = List.wrap(conflict_target) ++ fields
+        to_remove = if replace_changed?, do: List.wrap(conflict_target) ++ fields, else: fields
         replace = replace_all_fields!(:replace_all_except, schema, to_remove)
 
         if replace == [], do: raise(ArgumentError, "empty list of fields to update, use the `:replace` option instead")
diff --git a/test/ecto/repo_test.exs b/test/ecto/repo_test.exs
index 82775a182a..ac41607d83 100644
--- a/test/ecto/repo_test.exs
+++ b/test/ecto/repo_test.exs
@@ -1928,7 +1928,7 @@ defmodule Ecto.RepoTest do
       assert_received {:insert, %{source: "my_schema", on_conflict: {^fields, [], []}}}
     end
 
-    test "includes conflict target in the field list given to :replace_all_except" do
+    test "does not pass conflict target to :replace_all_except" do
       fields = [:map, :z, :yyy, :x]
 
       TestRepo.insert(%MySchema{id: 1},
@@ -1939,6 +1939,18 @@ defmodule Ecto.RepoTest do
       assert_received {:insert, %{source: "my_schema", on_conflict: {^fields, [], [:id]}}}
     end
 
+    test "passes conflict target to :replace_all_except when replace_changed is false" do
+      fields = [:map, :z, :yyy, :x, :id]
+
+      TestRepo.insert(%MySchema{id: 1},
+        on_conflict: {:replace_all_except, [:array]},
+        conflict_target: [:id],
+        replace_changed: false
+      )
+
+      assert_received {:insert, %{source: "my_schema", on_conflict: {^fields, [], [:id]}}}
+    end
+
     test "raises on empty-list of fields to update when :replace_all_except is given" do
       msg = "empty list of fields to update, use the `:replace` option instead"
 
@@ -1956,6 +1968,12 @@ defmodule Ecto.RepoTest do
       assert_received {:insert, %{source: "my_schema", on_conflict: {^fields, [], [:id]}}}
     end
 
+    test "includes conflict target in :replace_all when replace_changed is false" do
+      fields = [:map, :array, :z, :yyy, :x, :id]
+      TestRepo.insert(%MySchema{id: 1}, on_conflict: :replace_all, conflict_target: [:id], replace_changed: false)
+      assert_received {:insert, %{source: "my_schema", on_conflict: {^fields, [], [:id]}}}
+    end
+
     test "raises on empty-list of fields to update when :replace_all is given" do
       msg = "empty list of fields to update, use the `:replace` option instead"