Hello,

We have a query that is run almost each second and it's very important to
squeeze every other ms out of it. The query is:

SELECT c0."id" FROM "campaign_jobs" AS c0
WHERE (((c0."status" = $1) AND NOT (c0."id" = ANY($2))))
OR ((c0."status" = $3) AND (c0."failed_at" > $4))
OR ((c0."status" = $5) AND (c0."started_at" < $6))
ORDER BY c0."priority" DESC, c0."times_failed"
LIMIT $7
FOR UPDATE SKIP LOCKED

I added following index:

CREATE INDEX ON campaign_jobs(id, status, failed_at, started_at, priority
DESC, times_failed);

And it didn't help at all, even opposite - the planning phase time grew up
from ~2ms up to ~40 ms leaving execution time intact:

Limit (cost=29780.02..29781.27 rows=100 width=18) (actual
time=827.753..828.113 rows=100 loops=1)
-> LockRows (cost=29780.02..32279.42 rows=199952 width=18) (actual
time=827.752..828.096 rows=100 loops=1)
-> Sort (cost=29780.02..30279.90 rows=199952 width=18) (actual
time=827.623..827.653 rows=100 loops=1)
Sort Key: priority DESC, times_failed
Sort Method: external sort Disk: 5472kB
-> Seq Scan on campaign_jobs c0 (cost=0.00..22138.00
rows=199952 width=18) (actual time=1.072..321.410 rows=200000 loops=1)
Filter: (((status = 0) AND (id <> ALL
('{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,
23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,
43,44,45,46,47,48}'::integer[]))) OR ((status = 2) AND (failed_at >
'2017-06-22 03:18:09'::timestamp without time zone)) OR ((status = 1) AND
(started_at < '2017-06-23 03:11:09'::timestamp without time zone)))
Planning time: 40.734 ms
Execution time: 913.638 ms
(9 rows)

I see that query still went through the Seq Scan instead of Index Scan. Is
it due to poorly crafted index or because of query structure? Is it
possible to make this query faster?

Thanks