long running php script that loads a large amount of data
<p>I have a PHP script will be ran on a production web server only once.  The script loads a whole lot of db records and then iterates over them, json_decoding a field and checking it.  Some fields will be amended and saved back to the database.</p>

<p>The script will consume a lot of memory and will potentially run for 1hr or more.</p>

<p>What should I keep in mind with this type of script with regards to making sure it doesn’t cause the site to go down or any other potential hazards of such scripts.</p>

<p>The basic flow of the script is as follows:</p>

<pre><code>1. load all records from db table
2. iterate over each row
  2.1 json_decode specific field
  2.2 if a matching field is found then
      2.2.1 Change the value 
      2.2.2 Save back to the database
</code></pre>
