Add indices to Block.timestamp and BlockTransaction.block_id.

priv/repo/migrations/20180208010839_add_indices_to_block_and_block_transaction.exs

@@ -0,0 +1,8 @@
+defmodule Explorer.Repo.Migrations.AddIndicesToBlockAndBlockTransaction do
+  use Ecto.Migration
+
+  def change do
+    create index(:block_transactions, :block_id)
+    create index(:blocks, :timestamp)
+  end
+end