<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateArchivesTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('archives', function (Blueprint $table) {
            $table->increments('id');
            $table->string('url', 250)->unique();
            $table->string('filename', 250)->unique();
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('archives');
    }
}

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateArchivesTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('archives', function (Blueprint $table) {
            $table->increments('id');
            $table->string('url')->unique();
            $table->string('filename')->unique();
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('archives');
    }
}

--- 
+++ 
@@ -15,8 +15,8 @@
     {
         Schema::create('archives', function (Blueprint $table) {
             $table->increments('id');
-            $table->string('url')->unique();
-            $table->string('filename')->unique();
+            $table->string('url', 250)->unique();
+            $table->string('filename', 250)->unique();
             $table->timestamps();
         });
     }
Tweak the archives migration to respect the InnoDB key size constraint
