Partitioning and performance

I am testing partitioning of a large table. I am doing a range
partitioning based on a sequence col, which also acts as the primary
key. For inserts I am using a trigger which will redirect insert to
the right table based on the value of the primary key.

Based on my testing, I see that the insert speed is less than 10%
different than a non partitioned table. I am using SET
constraint_exclusion = on and I checked that via ANALYZE that the
planner does not consider non qualifying child tables.

yet, selects and updates based on the primary key show anywhere from
40 to 200% slowness as compared to non partition. One thing I notice
is that, even with partition pruning, the planner scans the base table
and the table matching the condition. Is that the additional overhead.

I am attaching below the output of analyze.

===========================
On a non partitioned table

explain select count(*) from tstesting.account where account_row_inst = 101 ;
Aggregate (cost=8.16..8.17 rows=1 width=0)
-> Index Only Scan using account_pkey on account (cost=0.14..8.16
rows=1 width=0)
Index Cond: (account_row_inst = 101)
(3 rows)

With partition pruning:

Aggregate (cost=8.45..8.46 rows=1 width=0)
-> Append (cost=0.00..8.44 rows=2 width=0)
-> Seq Scan on account (cost=0.00..0.00 rows=1 width=0)
Filter: (account_row_inst = 101)
-> Index Only Scan using account_part1_pkey on account_part1
(cost=0.42..8.44 rows=1 width=0)
Index Cond: (account_row_inst = 101)
(6 rows)

On a partitioned table, with no partition pruning.

explain analyze select count(*) from tstesting.account where
account_row_inst = 101 ;
Aggregate (cost=29.77..29.78 rows=1 width=0) (actual time=0.032..0.032
rows=1 loops=1)
-> Append (cost=0.00..29.76 rows=5 width=0) (actual time=0.029..0.029
rows=0 loops=1)
-> Seq Scan on account (cost=0.00..0.00 rows=1 width=0) (actual
time=0.000..0.000 rows=0 loops=1)
Filter: (account_row_inst = 101)
-> Index Only Scan using account_part1_pkey on account_part1
(cost=0.42..4.44 rows=1 width=0) (actual time=0.008..0.008 rows=0
loops=1)
Index Cond: (account_row_inst = 101)
Heap Fetches: 0
-> Index Only Scan using account_part2_pkey on account_part2
(cost=0.42..8.44 rows=1 width=0) (actual time=0.007..0.007 rows=0
loops=1)
Index Cond: (account_row_inst = 101)
Heap Fetches: 0
-> Index Only Scan using account_part3_pkey on account_part3
(cost=0.42..8.44 rows=1 width=0) (actual time=0.007..0.007 rows=0
loops=1)
Index Cond: (account_row_inst = 101)
Heap Fetches: 0
-> Index Only Scan using account_part4_pkey on account_part4
(cost=0.42..8.44 rows=1 width=0) (actual time=0.006..0.006 rows=0
loops=1)
Index Cond: (account_row_inst = 101)
Heap Fetches: 0
Planning time: 0.635 ms
Execution time: 0.137 ms
(18 rows)