Yes, that's how I solved it... and I totally agree that it's hard for the planner to guess what to do on the partitions. But maybe there should be something in the docs explaining the limitations ... I'm only asking for the biggest 100 ids from the table, so I thought maybe the planner would take the 100 biggest from all partitions or something like that and return me the 100 biggest from those results. It didn't and that's quite logical. What I meant is that I understand why the planner chooses this plan, but maybe it should be written somewhere in the docs that some plans will be worse after partitionning. Le Mardi 13 Décembre 2005 12:50, vous avez écrit : > I just saw that there is no where clause in the query, that you had > fed to explain plan. > you need to include a where clause based on id_machine column to see the > effect. > > On 12/13/05, Pandurangan R S <pandurangan.r.s@xxxxxxxxx> wrote: > > Did you set constraint_exclusion = true in postgresql.conf file? > > > > On 12/13/05, Marc Cousin <mcousin@xxxxxxxx> wrote: > > > Hi, > > > > > > I've been working on trying to partition a big table (I've never > > > partitioned a table in any other database till now). > > > Everything went ok, except one query that didn't work afterwards. > > > > > > I've put the partition description, indexes, etc ..., and the explain > > > plan attached. > > > > > > The query is extremely fast without partition (index scan backards on > > > the primary key) > > > > > > The query is : "select * from logs order by id desc limit 100;" > > > id is the primary key. > > > > > > It is indexed on all partitions. > > > > > > But the explain plan does full table scan on all partitions. > > > > > > While I think I understand why it is doing this plan right now, is > > > there something that could be done to optimize this case ? Or put a > > > warning in the docs about this kind of behaviour. I guess normally > > > someone would partition to get faster queries :) > > > > > > Anyway, I thought I should mention this, as it has been quite a > > > surprise. > > > > > > > > > > > > ---------------------------(end of > > > broadcast)--------------------------- TIP 1: if posting/reading through > > > Usenet, please send an appropriate subscribe-nomail command to > > > majordomo@xxxxxxxxxxxxxx so that your message can get through to the > > > mailing list cleanly > > > > -- > > Regards > > Pandu
