perf: Enhance index for token holders list (#9816)

* Enhance index for token holders list

* Separate index creation and deletion to different migrations

apps/explorer/priv/repo/migrations/20240404102510_enhance_index_for_token_holders_list.exs

@@ -0,0 +1,14 @@
+defmodule Explorer.Repo.Migrations.EnhanceIndexForTokenHoldersList do
+  use Ecto.Migration
+  @disable_ddl_transaction true
+  @disable_migration_lock true
+
+  def change do
+    create_if_not_exists(
+      index(:address_current_token_balances, ["token_contract_address_hash, value DESC, address_hash DESC"],
+        where: "address_hash != '\\x0000000000000000000000000000000000000000' AND value > 0",
+        concurrently: true
+      )
+    )
+  end
+end

apps/explorer/priv/repo/migrations/20240404102511_drop_outdated_index_for_token_holders_list.exs

@@ -0,0 +1,14 @@
+defmodule Explorer.Repo.Migrations.DropOutdatedIndexForTokenHoldersList do
+  use Ecto.Migration
+  @disable_ddl_transaction true
+  @disable_migration_lock true
+
+  def change do
+    drop_if_exists(
+      index(:address_current_token_balances, [:token_contract_address_hash],
+        where: "address_hash != '\\x0000000000000000000000000000000000000000' AND value > 0",
+        concurrently: true
+      )
+    )
+  end
+end