How optimize SQL query with DISTINCT ON and JOIN many values?

Question

I have a query like this where join ~6000 values

SELECT DISTINCT ON(user_id)
                user_id,
                finished_at as last_deposit_date,
                CASE When currency = 'RUB' Then amount_cents  END as last_deposit_amount_cents
            FROM    payments
            JOIN (VALUES (5),(22),(26)) --~6000 values
            AS v(user_id) USING (user_id)
            WHERE action = 'deposit' 
                AND success = 't'
                AND currency IN ('RUB')
            ORDER BY user_id, finished_at DESC

QUERY PLAN for query with many VALUES:

Unique  (cost=444606.97..449760.44 rows=19276 width=24) (actual time=6129.403..6418.317 rows=5991 loops=1)
  Buffers: shared hit=2386527, temp read=7807 written=7808
  ->  Sort  (cost=444606.97..447183.71 rows=1030695 width=24) (actual time=6129.401..6295.457 rows=1877039 loops=1)
        Sort Key: payments.user_id, payments.finished_at DESC
        Sort Method: external merge  Disk: 62456kB
        Buffers: shared hit=2386527, temp read=7807 written=7808
        ->  Nested Loop  (cost=0.43..341665.35 rows=1030695 width=24) (actual time=0.612..5085.376 rows=1877039 loops=1)
              Buffers: shared hit=2386521
              ->  Values Scan on "*VALUES*"  (cost=0.00..75.00 rows=6000 width=4) (actual time=0.002..4.507 rows=6000 loops=1)
              ->  Index Scan using index_payments_on_user_id on payments  (cost=0.43..54.78 rows=172 width=28) (actual time=0.010..0.793 rows=313 loops=6000)
                    Index Cond: (user_id = "*VALUES*".column1)
                    Filter: (success AND ((action)::text = 'deposit'::text) AND ((currency)::text = 'RUB'::text))
                    Rows Removed by Filter: 85
                    Buffers: shared hit=2386521
Planning time: 5.886 ms
Execution time: 6429.685 ms

I use PosgreSQL 10.8.0. Is there any chance to speed up this query?

I tried replacing DISTINCT with recursion:

WITH RECURSIVE t AS (
 (SELECT min(user_id) AS user_id FROM payments)
 UNION ALL
 SELECT (SELECT min(user_id) FROM payments  
 WHERE user_id > t.user_id      
 ) AS user_id FROM
t   
  WHERE t.user_id IS NOT NULL
 )
SELECT payments.* FROM t
JOIN (VALUES (5),(22),(26)) --~6000 VALUES
AS v(user_id) USING (user_id)
, LATERAL (
 SELECT user_id,
        finished_at as last_deposit_date,
        CASE When currency = 'RUB' Then amount_cents  END as last_deposit_amount_cents FROM payments            
        WHERE payments.user_id=t.user_id
            AND action = 'deposit' 
        AND success = 't'
        AND currency IN ('RUB')     
        ORDER BY finished_at DESC LIMIT 1
) AS payments

WHERE t.user_id IS NOT NULL;

But it turned out even slower.

Hash Join (cost=418.67..21807.22 rows=3000 width=24) (actual time=16.804..10843.174 rows=5991 loops=1) Hash Cond: (t.user_id = "VALUES".column1) Buffers: shared hit=6396763 CTE t -> Recursive Union (cost=0.46..53.73 rows=101 width=8) (actual time=0.142..1942.351 rows=237029 loops=1) Buffers: shared hit=864281 -> Result (cost=0.46..0.47 rows=1 width=8) (actual time=0.141..0.142 rows=1 loops=1) Buffers: shared hit=4 InitPlan 3 (returns $1) -> Limit (cost=0.43..0.46 rows=1 width=8) (actual time=0.138..0.139 rows=1 loops=1) Buffers: shared hit=4 -> Index Only Scan using index_payments_on_user_id on payments payments_2 (cost=0.43..155102.74 rows=4858092 width=8) (actual time=0.137..0.138 rows=1 loops=1) Index Cond: (user_id IS NOT NULL) Heap Fetches: 0 Buffers: shared hit=4 -> WorkTable Scan on t t_1 (cost=0.00..5.12 rows=10 width=8) (actual time=0.008..0.008 rows=1 loops=237029) Filter: (user_id IS NOT NULL) Rows Removed by Filter: 0 Buffers: shared hit=864277 SubPlan 2 -> Result (cost=0.48..0.49 rows=1 width=8) (actual time=0.007..0.007 rows=1 loops=237028) Buffers: shared hit=864277 InitPlan 1 (returns $3) -> Limit (cost=0.43..0.48 rows=1 width=8) (actual time=0.007..0.007 rows=1 loops=237028) Buffers: shared hit=864277 -> Index Only Scan using index_payments_on_user_id on payments payments_1 (cost=0.43..80786.25 rows=1619364 width=8) (actual time=0.007..0.007 rows=1 loops=237028) Index Cond: ((user_id IS NOT NULL) AND (user_id > t_1.user_id)) Heap Fetches: 46749 Buffers: shared hit=864277 -> Nested Loop (cost=214.94..21498.23 rows=100 width=32) (actual time=0.475..10794.535 rows=167333 loops=1) Buffers: shared hit=6396757 -> CTE Scan on t (cost=0.00..2.02 rows=100 width=8) (actual time=0.145..1998.788 rows=237028 loops=1) Filter: (user_id IS NOT NULL) Rows Removed by Filter: 1 Buffers: shared hit=864281 -> Limit (cost=214.94..214.94 rows=1 width=24) (actual time=0.037..0.037 rows=1 loops=237028) Buffers: shared hit=5532476 -> Sort (cost=214.94..215.37 rows=172 width=24) (actual time=0.036..0.036 rows=1 loops=237028) Sort Key: payments.finished_at DESC Sort Method: quicksort Memory: 25kB Buffers: shared hit=5532476 -> Index Scan using index_payments_on_user_id on payments (cost=0.43..214.08 rows=172 width=24) (actual time=0.003..0.034 rows=15 loops=237028) Index Cond: (user_id = t.user_id) Filter: (success AND ((action)::text = 'deposit'::text) AND ((currency)::text = 'RUB'::text)) Rows Removed by Filter: 6 Buffers: shared hit=5532473 -> Hash (cost=75.00..75.00 rows=6000 width=4) (actual time=2.255..2.255 rows=6000 loops=1) Buckets: 8192 Batches: 1 Memory Usage: 275kB -> Values Scan on "VALUES" (cost=0.00..75.00 rows=6000 width=4) (actual time=0.004..1.206 rows=6000 loops=1) Planning time: 7.029 ms Execution time: 10846.774 ms

Gordon Linoff · Accepted Answer · 2019-07-01 10:37:52Z

1

For this query:

SELECT DISTINCT ON (user_id)
       p.user_id,
       p.finished_at as last_deposit_date,
       (CASE WHEN p.currency = 'RUB' THEN p.amount_cents  END) as last_deposit_amount_cents
FROM payments p JOIN
     (VALUES (5),( 22), (26) --~6000 values
     ) v(user_id)
     USING (user_id)
WHERE p.action = 'deposit' AND
      p.success = 't' ND
      p.currency = 'RUB'
ORDER BY p.user_id, p.finished_at DESC;

I don't fully understand the CASE expression, because the WHERE is filtering out all other values.

That said, I would expect an index on (action, success, currency, user_id, finished_at desc) to be helpful.

answered Jul 1, 2019 at 10:37

Gordon Linoff

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