Thread: select slows from 3 seconds to 30 seconds
Hi folks.
I have the query below which when run takes approx 3 seconds. However when I
add the condition 'and w_ws_id = 10' onto the end changes to 30+ seconds.
Can anyone see why? I've included the explain for the long select.
select w_vin as key, w_vin, v_o_number as vista, v_status, s_stock_no, s_customer_order,
coalesce(d.r_registration,p.r_registration, w_reg_no) as
reg_no,w_arrival, w_updated::date,CURRENT_DATE-w_created::date as age, w_model, w_radio_code, w_key_no,
w_inspected,w_damage, w_walon_repair,w_collect_date, w_despatch_date, w_sheet, w_plates, w_accessories,
coalesce(p.d_des, d.d_des) as d_des, coalesce(p.de_des, d.de_des) as de_des, p.r_id as pdi, d.r_id as
delivery, o.o_id, o.state from walon left outer join request_details p on p.t_id = 'P' and
substring(p.r_chassisfrom '(.{11}$)') = w_vin left outer join request_details d on d.t_id = 'D' and
substring(d.r_chassisfrom '(.{11}$)') = w_vin left outer join order_details o on substring(o.o_vin from
'(.{11}$)')= w_vin left outer join stock s on substring(s.s_vin from '(.{11}$)') = w_vin left outer join vista v on
v.v_vin= w_vin where w_hide = 0.
--
Gary Stainburn
This email does not contain private or confidential material as it
may be snooped on by interested government parties for unknown
and undisclosed purposes - Regulation of Investigatory Powers Act, 2000
Gary Stainburn <gary.stainburn@ringways.co.uk> writes:
> I have the query below which when run takes approx 3 seconds. However when I
> add the condition 'and w_ws_id = 10' onto the end changes to 30+ seconds.
> Can anyone see why? I've included the explain for the long select.
You really ought to provide EXPLAIN ANALYZE output for both versions if
you want intelligent commentary --- otherwise we're just guessing.
But I would guess the problem is that the planner is way off about the
number of rows satisfying the joint condition --- it thinks two:
> -> Index Scan using walon_hide_index on walon (cost=0.00..85.04 rows=2 width=140)
> Index Cond: (w_hide = 0)
> Filter: (w_ws_id = 10)
This plan is good if there really are only a couple rows, but degrades
quickly if there are many...
regards, tom lane
On Saturday 05 May 2007 01:57, Tom Lane wrote: > Gary Stainburn <gary.stainburn@ringways.co.uk> writes: > > I have the query below which when run takes approx 3 seconds. However > > when I add the condition 'and w_ws_id = 10' onto the end changes to 30+ > > seconds. Can anyone see why? I've included the explain for the long > > select. > > You really ought to provide EXPLAIN ANALYZE output for both versions if > you want intelligent commentary --- otherwise we're just guessing. > > But I would guess the problem is that the planner is way off about the > > number of rows satisfying the joint condition --- it thinks two: > > -> Index Scan using walon_hide_index on walon > > (cost=0.00..85.04 rows=2 width=140) Index Cond: (w_hide = 0) > > Filter: (w_ws_id = 10) > > This plan is good if there really are only a couple rows, but degrades > quickly if there are many... > > regards, tom lane Thanks Tom I'll bear that in mind in future. The problem was fixed by running a 'vacuum analyse' so it looks like the planner was getting confused. Gary -- Gary Stainburn This email does not contain private or confidential material as it may be snooped on by interested government parties for unknown and undisclosed purposes - Regulation of Investigatory Powers Act, 2000