Question

in a simple partitioned table:

-- note: no records stored in base, only inheritors of base
create table base(
   base_id       bigint,
   base_tp       char(3) not null,
   ... );

create table base_abc(
   base_id       bigserial   primary key,
   base_tp       default 'abc'
                 check( base_tp = 'abc' ),
   ...
) inherits( base );


create table base_efg(
   base_id       bigserial   primary key,
   base_tp       default 'efg'
                 check( base_tp = 'efg' ),
   ...
) inherits( base );

if the the where clause in a query were to use base_tp, eg,

select * from base where ... and base_tp='abc'

would under 9.2 the query be optimized to select only table base_abc or would it, as it does currently, query a base, base_abc, and base_efg?

Answer 1

Well, this behaviour can be set via the constraint_exclusion config option. If it’s on, then only the partitions with matching constraint(s) will be accessed. But you should be careful, and choose partition instead in order to avoid a heavy performance hit. It’s just the same considering partitioned tables, but leaves others unaffected.

Have a look at its documentation.