As of Magento 2.3 it is no longer best practice to use flat catalog at all. Detailed info and justification for this is a little thin on the ground right now (updates should be made to answers here to reflect when more info is found.) Apparently, this is specifically *for* performance reasons. As this question is related to performance, this is relevant. [![enter image description here][1]][1] [1]: https://i.sstatic.net/3YGyY.png Whatever issues the Magento team have found with flat catalog must outweigh the benefits of converting EAV data to a flat structure. --- Some tweets that start to shed some light on this: * https://twitter.com/JigneX/status/1167552039813038087 * https://twitter.com/theTiagoSampaio/status/1168938250989395969 * https://twitter.com/lorenzi_jo/status/1171145687171383297