On May 22, 2012, at 9:57 AM, Simon Riggs wrote: > On 22 May 2012 06:50, Tom Lane <t...@sss.pgh.pa.us> wrote: > >> Currently, the planner keeps paths that appear to win on the grounds of >> either cheapest startup cost or cheapest total cost. It suddenly struck >> me that in many simple cases (viz, those with no LIMIT, EXISTS, cursor >> fast-start preference, etc) we could know a-priori that cheapest startup >> cost is not going to be interesting, and hence immediately discard any >> path that doesn't win on total cost. > > My experience is that most people don't provide a LIMIT explicitly > even when they know that's the desired behaviour. That's because > either they simply don't understand that SQL can return lots of rows, > or SQL knowledge isn't enough, or worse that people don't even know > that specifying it would alter query plans. > > Regrettably the current planning of LIMIT clauses causes more problems > so in many cases these have been explicitly removed from SQL by > developers that know how many rows they wish to see. > > I would have proposed a default-LIMIT parameter before now, but for > that last point.
this sounds like a total disaster to me ... why in the world should we have a default LIMIT parameter? i guess if somebody is not able to use LIMIT he should better not touch the DB. we clearly cannot fix incompetence by adding parameters. regards, hans -- Cybertec Schönig & Schönig GmbH Gröhrmühlgasse 26 A-2700 Wiener Neustadt, Austria Web: http://www.postgresql-support.de -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers