Add more debug info to processing of logical message offsets

If we see transient errors caused by the violation of our assumptions
about WAL offset's monotonic growth, this should have debug that.

packages/sync-service/lib/electric/postgres/replication_client.ex

@@ -150,7 +150,7 @@ defmodule Electric.Postgres.ReplicationClient do
       ) do
     Logger.debug("XLogData: wal_start=#{wal_start}, wal_end=#{wal_end}")
 
-    state = update_received_wal(state, wal_end)
+    state = update_received_wal(:xlog_data, state, wal_start, wal_end)
 
     rest
     |> Decoder.decode()
@@ -185,7 +185,9 @@ defmodule Electric.Postgres.ReplicationClient do
   end
 
   def handle_data(<<@repl_msg_primary_keepalive, wal_end::64, _clock::64, reply>>, state) do
-    state = update_received_wal(state, wal_end)
+    Logger.debug("Primary Keepalive: wal_end=#{wal_end} reply=#{reply}")
+
+    state = update_received_wal(:keepalive, state, nil, wal_end)
 
     messages =
       case reply do
@@ -220,11 +222,11 @@ defmodule Electric.Postgres.ReplicationClient do
   defp current_time(), do: System.os_time(:microsecond) - @epoch
 
   # wal can be 0 if the incoming logical message is e.g. Relation.
-  defp update_received_wal(state, 0), do: state
+  defp update_received_wal(_step, state, _, 0), do: state
 
-  defp update_received_wal(%{received_wal: wal} = state, wal), do: state
+  defp update_received_wal(_step, %{received_wal: wal} = state, _, wal), do: state
 
-  defp update_received_wal(state, wal) when wal > state.received_wal,
+  defp update_received_wal(_step, state, _, wal) when wal > state.received_wal,
     do: %{state | received_wal: wal}
 
   defp update_applied_wal(state, wal) when wal > state.applied_wal,