Re: Postgres: Queries are too slow after upgrading to PG17 from PG15

On 15/5/2025 07:33, Sajith Prabhakar Shetty wrote:
> Hi,
>
>
> Most of the queries got slower after upgrading our postgres from version
> 15 to 17 using pg_upgrade. I reconfirmed that "vacuum full, analyze"
> were all taken care.
>
> To debug, instead of upgrade, I installed two instances one with
> postgres 15 and another postgres 17 with the same application dump restored.
>
> Now surprisingly one of the query i took from application which used to
> execute in 2s in PG15, is now taking 1min+ in PG17. I also observed that
> some of the operations involving DML operations slowed down too in PG17.
>
> Explain plan of the two queries almost same, all the joins and paths
> used are exactly same.
>
> Could anybody please provide some insights here?
Curious, the difference in Index Only Scan node:

-> Index Scan using stream_file_pkey on stream_file sf
(cost=1.63..1.86 rows=1 width=8)
(actual time=0.006..0.006 rows=1 loops=598916)
Index Cond: (id = sdo.stream_file_id)
Filter: (component_id = ANY

-> Index Only Scan using ui_stream_file_id_component on stream_file sf
(cost=0.43..0.51 rows=1 width=8)
(actual time=0.014..0.014 rows=1 loops=598916)
Index Cond: ((id = sdo.stream_file_id) AND (component_id = ANY

Each time the index scan is 2.5 times slower on PG17. But:

PG 15:
Buffers: shared hit=2338397 read=57267
I/O Timings: shared read=3384.286

PG 17:
Buffers: shared hit=1909772 read=9933
I/O Timings: shared read=686.506

If I'm not mistaken, it seems like an insight.

--
regards, Andrei Lepikhov