Add :wrap_in_transaction option to explain

integration_test/myxql/explain_test.exs

@@ -10,7 +10,7 @@ defmodule Ecto.Integration.ExplainTest do
       explain = TestRepo.explain(:all, from(p in Post, where: p.title == "title"), timeout: 20000)
 
       assert explain =~
-        "| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |"
+               "| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |"
 
       assert explain =~ "p0"
       assert explain =~ "SIMPLE"
@@ -24,7 +24,9 @@ defmodule Ecto.Integration.ExplainTest do
     end
 
     test "update" do
-      explain = TestRepo.explain(:update_all, from(p in Post, update: [set: [title: "new title"]]))
+      explain =
+        TestRepo.explain(:update_all, from(p in Post, update: [set: [title: "new title"]]))
+
       assert explain =~ "UPDATE"
       assert explain =~ "p0"
     end
@@ -37,10 +39,20 @@ defmodule Ecto.Integration.ExplainTest do
 
     test "map format" do
       [explain] = TestRepo.explain(:all, Post, format: :map)
-      keys = explain["query_block"] |> Map.keys
+      keys = explain["query_block"] |> Map.keys()
       assert Enum.member?(keys, "cost_info")
       assert Enum.member?(keys, "select_id")
       assert Enum.member?(keys, "table")
     end
+
+    test "explain without rolling back" do
+      {:ok, {:ok, explain}} =
+        TestRepo.transaction(fn ->
+          TestRepo.explain(:delete_all, Post, wrap_in_transaction: false, timeout: 20000)
+        end)
+
+      assert explain =~ "DELETE"
+      assert explain =~ "p0"
+    end
   end
 end

integration_test/pg/explain_test.exs

@@ -81,4 +81,22 @@ defmodule Ecto.Integration.ExplainTest do
     assert explain =~ ~r/Node Type:/
     assert explain =~ ~r/Relation Name:/
   end
+
+  test "explain without rolling back" do
+    TestRepo.insert!(%Post{})
+    assert [%Post{}] = TestRepo.all(Post)
+
+    {:ok, {:ok, explain}} =
+      TestRepo.transaction(fn ->
+        TestRepo.explain(:delete_all, Post,
+          analyze: true,
+          wrap_in_transaction: false,
+          timeout: 20000
+        )
+      end)
+
+    assert explain =~ "Delete on posts p0"
+    assert explain =~ "cost="
+    assert TestRepo.all(Post) == []
+  end
 end

integration_test/tds/explain_test.exs

@@ -7,7 +7,9 @@ defmodule Ecto.Integration.ExplainTest do
 
   describe "explain" do
     test "select" do
-      explain = TestRepo.explain(:all, from(p in Post, where: p.title == "explain_test", limit: 1))
+      explain =
+        TestRepo.explain(:all, from(p in Post, where: p.title == "explain_test", limit: 1))
+
       assert explain =~ "| Rows | Executes |"
       assert explain =~ "| Parallel | EstimateExecutions |"
       assert explain =~ "SELECT TOP(1)"
@@ -21,7 +23,9 @@ defmodule Ecto.Integration.ExplainTest do
     end
 
     test "update" do
-      explain = TestRepo.explain(:update_all, from(p in Post, update: [set: [title: "new title"]]))
+      explain =
+        TestRepo.explain(:update_all, from(p in Post, update: [set: [title: "new title"]]))
+
       assert explain =~ "UPDATE"
       assert explain =~ "p0"
       assert explain =~ "new title"
@@ -32,5 +36,15 @@ defmodule Ecto.Integration.ExplainTest do
         TestRepo.explain(:all, from(p in "posts", select: p.invalid, where: p.invalid == "title"))
       end)
     end
+
+    test "explain without rolling back" do
+      {:ok, {:ok, explain}} =
+        TestRepo.transaction(fn ->
+          TestRepo.explain(:delete_all, Post, wrap_in_transaction: false, timeout: 20000)
+        end)
+
+      assert explain =~ "DELETE"
+      assert explain =~ "p0"
+    end
   end
 end

lib/ecto/adapters/sql.ex

@@ -434,8 +434,8 @@ defmodule Ecto.Adapters.SQL do
 
   Adapter          | Supported opts
   ---------------- | --------------
-  Postgrex         | `analyze`, `verbose`, `costs`, `settings`, `buffers`, `timing`, `summary`, `format`, `plan`
-  MyXQL            | `format`
+  Postgrex         | `analyze`, `verbose`, `costs`, `settings`, `buffers`, `timing`, `summary`, `format`, `plan`, `wrap_in_transaction`
+  MyXQL            | `format`, `wrap_in_transaction`
 
   All options except `format` are boolean valued and default to `false`.
 
@@ -447,6 +447,10 @@ defmodule Ecto.Adapters.SQL do
     * Postgrex: `:map`, `:yaml` and `:text`
     * MyXQL: `:map` and `:text`
 
+  The `wrap_in_transaction` option is a boolean that controls whether the command is run inside of a
+  transaction that is rolled back. This is useful when, for example, you'd like to use `analyze: true`
+  on an update or delete query without modifying data. Defaults to `true`.
+
   The `:plan` option in Postgrex can take the values `:custom` or `:fallback_generic`. When `:custom`
   is specified, the explain plan generated will consider the specific values of the query parameters
   that are supplied. When using `:fallback_generic`, the specific values of the query parameters will
@@ -508,10 +512,11 @@ defmodule Ecto.Adapters.SQL do
   def explain(repo, operation, queryable, opts \\ [])
 
   def explain(repo, operation, queryable, opts) when is_atom(repo) or is_pid(repo) do
-    explain(Ecto.Adapter.lookup_meta(repo), operation, queryable, opts)
+    wrap_in_transaction? = Keyword.get(opts, :wrap_in_transaction, true)
+    explain(Ecto.Adapter.lookup_meta(repo), operation, queryable, wrap_in_transaction?, opts)
   end
 
-  def explain(%{repo: repo} = adapter_meta, operation, queryable, opts) do
+  def explain(%{repo: repo} = adapter_meta, operation, queryable, true, opts) do
     Ecto.Multi.new()
     |> Ecto.Multi.run(:explain, fn _, _ ->
       {prepared, prepared_params} = to_sql(operation, repo, queryable)
@@ -528,6 +533,11 @@ defmodule Ecto.Adapters.SQL do
     end
   end
 
+  def explain(%{repo: repo} = adapter_meta, operation, queryable, false, opts) do
+    {prepared, prepared_params} = to_sql(operation, repo, queryable)
+    sql_call(adapter_meta, :explain_query, [prepared], prepared_params, opts)
+  end
+
   @doc @disconnect_all_doc
   @spec disconnect_all(
           pid | Ecto.Repo.t() | Ecto.Adapter.adapter_meta(),