Strange behavior of child table.

Hi All,

I have created partition on table Round_Action , which has 3 child partition
tables.

When I am firing a simple select query with limit on parent table it is
taking huge time to execute. But when I am firing this query directly on
child table it is taking few milliseconds.

EXP.
select * from Round_Action where action_id =50000 limit 100 → execution time
80 sec

select * from Round_Action_CH1 action_id =50000 limit 100 → execution time
0.1 sec

Round_Action is the parent table and has no record in the tables, all the
records are lying in child tables.

Table is having index on action_id.

Partition is trigger based.
Postgres Version : (PostgreSQL) 8.4.6

Why there is difference in execution time? What I am doing wrong?

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Thanks & regards,
JENISH