Hi, > hi, all > NOTE: Version is 8.4 Fedora 20 X86_64
Why don't you play on 9.3 or later? 8.4 is now on the edge to EOL. > for understanding optimizer's internals, I set debug_print_plan=on > and created two tables as follows : > > create table Reserves (sid integer, bid integer,day date,rname char(25)); > create table Sailors(sid integer,sname char(25),rating integer,age real); > > and add 1,000,000 records for each. > > and execute the cmd: > > select S.rating,count(*) > from Sailors S > where S.rating > 5 and S.age = 20 > group by S.rating; > > but from the log, I only found the final selected planTree, so I want to > ask: > what should I do if I want to see the other alternative planTrees? any > advice will be apprecitaed! Forcing another plan by configuration parameters would help. http://www.postgresql.org/docs/9.3/static/runtime-config-query.html For example, "set enable_hashagg to off" makes the planner to try to avoid using HashAggregate for grouping. If you got a plan using HashAgregate, you will get another one using GroupAggregate by that. What you can do otherwise would be building PG with CFLAGS="-DOPTIMIZER_DEBUG". This will show you a bit more than debug_print_plan, but the query you mentioned is too simple so that planner has almost no alternative. Creating some index (say, on age) would give planner some alternatives. Have a good day, -- Kyotaro Horiguchi NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
