On 2019-Aug-05, Jeremy Finzel wrote: > Thanks Tom. So, this is a very general question, but would it be possible > to develop that feature into BRIN, given what it stores? Even if it does > not have ordering information, doesn't it know which blocks would contain > the lowest values, so it could choose to do a "bitmap scan ordered sort" or > something, depending on the number of rows sought? Or is the problem that > it has no way of determining what value actually would be the "minimum" > without the query specifying a particular date, such as less than > "2013-04-01"? For btrees, we have planagg.c which transforms min() and max() into subqueries (SELECT .. WHERE ... ORDER BY .. LIMIT 1). In a BRIN index, you could execute the search by scanning the index to determine which ranges contain the least/greatest values, and then using a bitmap scan to scan those. I'm not sure that this is a transformation that can be applied cleanly, since that thing I describe doesn't look to be a "subquery". But maybe it can -- I think you'd need a special executor node. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
