Remember the generated stream_id across batches of events being appeneded.

lib/event_store/sql/statements/insert_events.sql.eex

@@ -57,20 +57,24 @@ WITH
     SET stream_version = stream_version + $2::bigint
     WHERE stream_id = 0
     RETURNING stream_version - $2::bigint as initial_stream_version
+  ),
+  linked_stream_events AS (
+    INSERT INTO "<%= schema %>".stream_events
+    (
+      event_id,
+      stream_id,
+      stream_version,
+      original_stream_id,
+      original_stream_version
+    )
+    SELECT
+      new_events_indexes.event_id,
+      0,
+      linked_stream.initial_stream_version + new_events_indexes.index,
+      stream.stream_id,
+      new_events_indexes.stream_version
+    FROM
+      new_events_indexes, linked_stream, stream
   )
-INSERT INTO "<%= schema %>".stream_events
-(
-  event_id,
-  stream_id,
-  stream_version,
-  original_stream_id,
-  original_stream_version
-)
-SELECT
-  new_events_indexes.event_id,
-  0,
-  linked_stream.initial_stream_version + new_events_indexes.index,
-  stream.stream_id,
-  new_events_indexes.stream_version
-FROM
-  new_events_indexes, linked_stream, stream;
+
+SELECT stream_id from stream;

lib/event_store/sql/statements/insert_events_any_version.sql.eex

@@ -57,20 +57,24 @@ WITH
     SET stream_version = stream_version + $2::bigint
     WHERE stream_id = 0
     RETURNING stream_version - $2::bigint as initial_stream_version
+  ),
+  linked_stream_events AS (
+    INSERT INTO "<%= schema %>".stream_events
+    (
+      event_id,
+      stream_id,
+      stream_version,
+      original_stream_id,
+      original_stream_version
+    )
+    SELECT
+      new_events_indexes.event_id,
+      0,
+      linked_stream.initial_stream_version + new_events_indexes.index,
+      stream.stream_id,
+      stream.initial_stream_version + new_events_indexes.index
+    FROM
+      new_events_indexes, linked_stream, stream
   )
-INSERT INTO "<%= schema %>".stream_events
-(
-  event_id,
-  stream_id,
-  stream_version,
-  original_stream_id,
-  original_stream_version
-)
-SELECT
-  new_events_indexes.event_id,
-  0,
-  linked_stream.initial_stream_version + new_events_indexes.index,
-  stream.stream_id,
-  stream.initial_stream_version + new_events_indexes.index
-FROM
-  new_events_indexes, linked_stream, stream;
+
+SELECT stream_id from stream;

lib/event_store/storage/appender.ex

@@ -20,17 +20,19 @@ defmodule EventStore.Storage.Appender do
       events
       |> Stream.map(&encode_uuids/1)
       |> Stream.chunk_every(1_000)
-      |> Enum.each(fn batch ->
+      |> Enum.reduce(stream_id, fn batch, stream_id ->
         event_count = length(batch)
 
-        with :ok <- insert_event_batch(conn, stream_id, stream_uuid, batch, event_count, opts) do
+        with {:ok, new_stream_id} <-
+               insert_event_batch(conn, stream_id, stream_uuid, batch, event_count, opts) do
           Logger.debug("Appended #{event_count} event(s) to stream #{inspect(stream_uuid)}")
-
-          :ok
+          new_stream_id
         else
           {:error, error} -> throw({:error, error})
         end
       end)
+
+      :ok
     catch
       {:error, error} = reply ->
         Logger.warning(
@@ -110,9 +112,14 @@ defmodule EventStore.Storage.Appender do
     params = [stream_id_or_uuid, event_count] ++ build_insert_parameters(events)
 
     case Postgrex.query(conn, statement, params, opts) do
-      {:ok, %Postgrex.Result{num_rows: 0}} -> {:error, :not_found}
-      {:ok, %Postgrex.Result{}} -> :ok
-      {:error, error} -> handle_error(error)
+      {:ok, %Postgrex.Result{num_rows: 0}} ->
+        {:error, :not_found}
+
+      {:ok, %Postgrex.Result{rows: [[stream_id]]}} ->
+        {:ok, stream_id}
+
+      {:error, error} ->
+        handle_error(error)
     end
   end
 

lib/event_store/streams/stream.ex

@@ -344,9 +344,7 @@ defmodule EventStore.Streams.Stream do
 
       append_to_stream(conn, stream_uuid, expected_version, events, opts)
     else
-      # We should never get here, but just in case we break something in another
-      # part of the app, this will give us better output in the tests.
-      {:error, :already_retried_once}
+      {:error, {:already_retried_once, :duplicate_stream_uuid}}
     end
   end
 

test/test_helper.exs

@@ -1,3 +1,3 @@
-exclude = [:ignore, :manual, :migration, :slow]
+exclude = [:ignore, :manual, :migration]
 
 ExUnit.start(exclude: exclude)