What is in it

One row for each product or variation and each attribute value it carries, with a flag for whether that row is in stock and, for a variation, which parent it belongs to. WooCommerce’s own layered navigation uses it when it is on, and WooCommerce has done so since version 6.

Why a filter wants it

With the table, one question to the database gives the number of products behind a value, with sold-out variations handled correctly. Without it, a filter must load product ids into PHP or count by parent, and both are slower or less accurate on a large catalogue. Siftwren reads the table in SQL, along with WooCommerce’s other lookup table, the term relationships and the posts table, and nothing else. It never writes to any of them.

Where to switch it on

In WooCommerce, open Settings → Products → Advanced and look for the setting about the product attributes lookup table. That is also where the link in the plugin’s own warning goes.

What Siftwren does when it is off

The filter keeps working. Its numbers fall back to the taxonomy, which means a variable product counts by its parent and a sold-out variation is not told apart from one in stock. On the plugin’s own screens, the settings page and the filter set editor, a warning says so to the people who can change it. It disappears the moment WooCommerce’s setting is on, and shoppers never see it.

If your counts disagree with your lists, this is the first thing to look at. The wrong-counts guide covers the other causes.