Re: Query performance issue

"Subquery Scan on rec (cost=1628601.89..1676580.92 rows=7381 width=41)
(actual time=22171.986..23549.079 rows=1236042 loops=1)" " Filter:
(rec.mpos = 1)" " Rows Removed by Filter: 228737" " Buffers: shared hit=45
read=1166951" " I/O Timings: read=29.530" " -> WindowAgg
(cost=1628601.89..1658127.45 rows=1476278 width=49) (actual
time=22171.983..23379.219 rows=1464779 loops=1)" " Buffers: shared hit=45
read=1166951" " I/O Timings: read=29.530" " -> Sort
(cost=1628601.89..1632292.58 rows=1476278 width=41) (actual
time=22171.963..22484.044 rows=1464779 loops=1)" " Sort Key:
receiving_item_delivered_received.serial_no,
receiving_item_delivered_received.eventtime DESC" " Sort Method: quicksort
Memory: 163589kB" " Buffers: shared hit=45 read=1166951" " I/O Timings:
read=29.530" " -> Gather (cost=1000.00..1477331.13 rows=1476278 width=41)
(actual time=1.296..10428.060 rows=1464779 loops=1)" " Workers Planned: 2" "
Workers Launched: 2" " Buffers: shared hit=39 read=1166951" " I/O Timings:
read=29.530" " -> Parallel Seq Scan on receiving_item_delivered_received
(cost=0.00..1328703.33 rows=615116 width=41) (actual time=1.262..10150.325
rows=488260 loops=3)" " Filter: (((COALESCE(serial_no, ''::character
varying))::text <> ''::text) AND ((eventtype)::text =
'LineItemdetailsReceived'::text) AND ((replenishmenttype)::text =
'DC2SWARRANTY'::text))" " Rows Removed by Filter: 6906258" " Buffers:
shared hit=39 read=1166951" " I/O Timings: read=29.530" "Planning Time:
0.375 ms" "Execution Time: 23617.348 ms"

That is doing a lot of reading from disk. What do you have shared_buffers
set to? I'd expect better cache hits unless it is quite low or this is a
query that differs greatly from the typical work.

Also, did you try adding the index I suggested? That lowest node has 488k
rows coming out of it after throwing away 6.9 million. I would expect an
index on only eventtype, replenishmenttype to be quite helpful. I don't
assume you have tons of rows where serial_no is null.