Hi, pg_attribute is one of the biggest table in a new cluster, and often the biggest table in production clusters. Its size is also quite relevant in memory, due to all the TupleDescs we allocate.
I just noticed that the new attcompression increased the size not just by 1 byte, but by 4, due to padding. While an increase from 112 to 116 bytes isn't the end of the world, it does seem worth considering using existing unused bytes instead? If we moved attcompression to all the other bool/char fields, we'd avoid that size increase, as there's an existing 2 byte hole. Of course there's the argument that we shouldn't change the column order for existing SELECT * queries, but the existing placement already does (the CATALOG_VARLEN columns follow). Greetings, Andres Freund
