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Using a Flat Catalog
Magento typically stores catalog data in multiple tables, based on the Entity-Attribute-Value (EAVEntity Attribute Value) model. Because product attributes are stored in many tables, SQL queries are sometimes long and complex.
In contrast, a flat catalog creates new tables on the fly, where each row contains all the necessary data about a product or categoryA set of products that share particular characteristics or attributes.. A flat catalog is updated automatically—either every minute, or according to your cron job. Flat catalog indexing can also speed up the processing of catalog and cart price rules. A catalog with as many as 500,000 SKUs can be indexed quickly as a flat catalog.