Re: Question on execution plan and suitable index

On Mon, 2026-02-16 at 00:34 +0530, yudhi s wrote:
> It's postgres version 17. We are having a critical UI query which runs for ~7 seconds+. The requirement is to bring down the response time within ~1 sec. Now in this plan , If i read this correctly, the below section is consuming a significant amount of resources and should be addressed. i.e. "Full scan of table "orders" and Nested loop with event_audit_log table".
>
> Below is the query and its complete plan:- 
> https://gist.github.com/databasetech0073/f564ac23ee35d1f0413980fe4d00efa9
>
> I am a bit new to the indexing strategy in postgres. My question is, what suitable index should we create to cater these above?
>
> 1)For table event_audit_log:- Should we create composite Index on column (request_id,created_at,event_comment_text) or should we create the covering index i.e. just on two column (request_id,created_at) with "include" clause for "event_comment_text". How and when the covering index indexes should be used here in postgres. Want to understand from experts? 
> 2)Similarly for table orders:- Should we create a covering index on column (entity_id,due_date,order_type) with include clause (firm_dspt_case_id). Or just a composite index (entity_id,due_date,order_type).
> 3)Whether the column used as range operator (here created_at or due_date) should be used as leading column in the composite index or is it fine to keep it as non leading?
>
> ->  Nested Loop  (cost=50.06..2791551.71 rows=3148 width=19) (actual time=280.735..7065.313 rows=57943 loops=3)
>   Buffers: shared hit=10014901
>   ->  Hash Join  (cost=49.49..1033247.35 rows=36729 width=8) (actual time=196.407..3805.755 rows=278131 loops=3)
>  Hash Cond: ((ord.entity_id)::numeric = e.entity_id)
>  Buffers: shared hit=755352
>  ->  Parallel Seq Scan on orders ord  (cost=0.00..1022872.54 rows=3672860 width=16) (actual time=139.883..3152.627 rows=2944671 loops=3)
>   Filter: ((due_date >= '2024-01-01'::date) AND (due_date <= '2024-04-01'::date) AND (order_type = ANY ('{TYPE_A,TYPE_B}'::text[])))
>   Rows Removed by Filter: 6572678
>   Buffers: shared hit=755208

You are selecting a lot of rows, so the query will never be really cheap.
But I agree that an index scan should be a win.

If the condition on "order_type" is always the same, a partial index is ideal:

CREATE INDEX ON orders (due_date) WHERE order_type IN ('TYPE_A', 'TYPE_B');

Otherwise, I'd create two indexes: one on "order_type" and one on "due_date".

Yours,
Laurenz Albe