felix@xxxxxxxxxxx writes: > However, in the process of investigating this, my boss found something > which we do not understand. A table with a primary key 'id' takes 200 > seconds to SELECT MAX(id), but is as close to instantaneous as you'd > want for SELECT ID ORDER BY ID DESC LIMIT 1. I understand why > count(*) has to traverse all records, but why does MAX have to? This > table has about 750,000 rows, rather puny. As I understand it, because aggregates in PG are extensible (the query planner just knows it's calling some function), MAX isn't specially handled--the planner doesn't know it's equivalent to the other query. There has been some talk of special-casing this, but I'm not sure where it lead--you might check the archives. -Doug ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
