The code to delete old records is executed on each page load, after all other Admin Tools features have run. In practice, this means that 100 old records are deleted every time someone accesses your site, they don't raise a security exception and the page is not served from the Joomla cache.
If you know how to truncate the table using phpMyAdmin it is, of course, the fastest way to do it. We haven't documented this option since it's a bit over the head of many of our users and we don't want to confuse them. So, answering your question, yes, truncating the table would be faster and wouldn't cause any functional problems.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
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