Remove order from SkippedReceipts and add appropriate indexes

lib/explorer/skipped_receipts.ex

@@ -13,7 +13,6 @@ defmodule Explorer.SkippedReceipts do
       left_join: receipt in assoc(transaction, :receipt),
       select: fragment("hash"),
       where: is_nil(receipt.id),
-      order_by: [desc: fragment("lower(hash)")],
       limit: ^count
     Repo.all(transactions)
   end

priv/repo/migrations/20180212214442_create_transaction_receipts.exs

@@ -12,6 +12,7 @@ defmodule Explorer.Repo.Migrations.CreateTransactionReceipts do
     end
 
     create index(:transaction_receipts, :index)
-    create unique_index(:transaction_receipts, [:transaction_id, :index])
+    create index(:transaction_receipts, :status)
+    create unique_index(:transaction_receipts, :transaction_id)
   end
 end

priv/repo/migrations/20180212222309_create_logs.exs

@@ -11,7 +11,16 @@ defmodule Explorer.Repo.Migrations.CreateLogs do
       add :first_topic, :string, null: true
       add :second_topic, :string, null: true
       add :third_topic, :string, null: true
+      add :fourth_topic, :string, null: true
       timestamps null: false
     end
+
+    create index(:logs, :index)
+    create index(:logs, :first_topic)
+    create index(:logs, :second_topic)
+    create index(:logs, :third_topic)
+    create index(:logs, :fourth_topic)
+    create index(:logs, :address_id)
+    create unique_index(:logs, :transaction_receipt_id)
   end
 end

test/explorer/skipped_transactions_test.exs

@@ -44,12 +44,6 @@ defmodule Explorer.SkippedReceiptsTest do
       assert SkippedReceipts.first(1) == ["0xBEE75"]
     end
 
-    test "returns up to the requested number of skipped transaction hashes in insert order" do
-      insert(:transaction, %{hash: "0xBEE75"})
-      insert(:transaction, %{hash: "0xBE475"})
-      assert SkippedReceipts.first(1) == ["0xBEE75"]
-    end
-
     test "returns all the skipped transaction hashes in random order" do
       insert(:transaction, %{hash: "0xBEE75"})
       insert(:transaction, %{hash: "0xBE475"})