Yes, that join is concerning (red text below). The conditions all need to be checked so they are independent.
The query (with consistent obfuscation) is below :
select distinct
a.sale_id
, a.test_date
, a.product_id as original_product_id
,vw2.product_id
, a.volume as volume
,b.pair_rank
from not_sold_locations a
inner join vw_product vw2 using (product_group_name,product_class_code,product_type_code,sale_end_date)
inner join product_mapping b on a.product_group_name = b.left_product_group_name and
a.product_node_name = b.left_product_node and
a.product_type_code = b.left_product and
vw2.product_node_name = b.right_product_node and
vw2.product_group_name = b.right_product_group_name and
vw2.product_type_code = b.right_product
inner join mapping_ref i on vw2.product_group_name || '.' || vw2.product_node_name = i.product_node_name and
vw2.product_class_code = i.product_class_code and
vw2.product_type_code = i.product_type_code and
vw2.sale_end_date between i.first_product_date and i.last_product_date;
not_sold_locations(a) has 836 rows
vw_product (vw2) has 785k rows and is a view that joins 11 tables together to have a consolidated view of all products, sales locations, etc
product_mapping (b) has 2520 rows
mapping_ref (i) has 178 rows
On Thu, Sep 27, 2018 at 2:52 PM Justin Pryzby <pryzby@xxxxxxxxxxxxx> wrote:
On Thu, Sep 27, 2018 at 01:08:05PM -0400, Arjun Ranade wrote:
> When I look at the EXPLAIN ANALYZE output, it seems that it's using a
> drastically different query plan for the INSERT+SELECT than SELECT by
> itself.
The fast, SELECT plan is using parallel query, which isn't available for INSERT+SELECT:
https://www.postgresql.org/docs/current/static/when-can-parallel-query-be-used.html
|Even when it is in general possible for parallel query plans to be generated, the planner will not generate them for a given query if any of the following are true:
|The query writes any data or locks any database rows.
Using parallel query in this case happens to mitigate the effects of the bad
plan.
I see Tom responded, and you got an improvement by changing join threshold.
But I think you could perhaps get an better plan if the rowcount estimates were
fixed. That's more important than probably anything else - changing settings
is only a workaround for bad estimates.
In the slow/INSERT plan, this join is returning 55000x more rows than expected
(not 55k more: 55k TIMES more).
7. 26,937.132 401,503.136 ↓ 55,483.7 332,902 1
Nested Loop (cost=1,516.620..42,244.240 rows=6 width=84) (actual time=311.021..401,503.136 rows=332,902 loops=1)
Join Filter: (((papa_echo.oscar_bravo)::text = (five_hotel.tango_november)::text) AND ((papa_echo.lima_tango)::text = (five_hotel.lima_mike)::text) AND ((xray_juliet1.juliet)::text = (five_hotel.papa_victor)::text))
Rows Removed by Join Filter: 351664882
Buffers: shared hit=8570619 read=6
First question is if all those conditions are independent? Or if one of those
conditions also implies another, which is confusing the planner.
Justin
