Your concern is valid. Whenever complexity is abstracted away you may suddenly introduce an exponential order algorithm in an otherwise simple looking query. H

Your concern is valid. Whenever complexity is abstracted away you may suddenly introduce an exponential order algorithm in an otherwise simple looking query. Having said so, Postgresql has actually surprised me very little throughout time. The planner's "reasoning" is quite comprehensible. Inevitably I trigger a slow plan here and there but, once identified, correction is usually straightforward. My overall opinion is that postgresql has quite solid theoretical foundations and it shows. What I mean is that, in advanced stuff, there'll always be some "magic", and that postgresql has the least amount of black box magic I've ever seen on a RDBMS (I'm looking at you, Oracle). (Postgresql has been my non-clustered database of choice since about 2004. I'm definitely biased.)