RE: Big performance slowdown from 11.2 to 13.3 - Mailing list pgsql-performance

I did try 2000MB work_mem and 16 multiplier 😊 It seems to plateau at 2GB no matter what. This is what the explain had:

HashAggregate  (cost=1774568.21..1774579.21 rows=200 width=1260) (actual time=94618.303..1795311.542 rows=722853
loops=1)
  Group Key: assessmenticcqa_raw.iccqar_iccassmt_fk
  Batches: 1  Memory Usage: 1277985kB
  Buffers: shared hit=14 read=169854, temp read=15777 written=27588
  ->  HashAggregate  (cost=1360804.75..1374830.63 rows=1402588 width=56) (actual time=30753.022..45384.558
rows=13852618loops=1)
 
        Group Key: assessmenticcqa_raw.iccqar_iccassmt_fk, assessmenticcqa_raw.iccqar_ques_code
        Batches: 5  Memory Usage: 2400305kB  Disk Usage: 126560kB
        Buffers: shared read=169851, temp read=15777 written=27588
        ->  Seq Scan on assessmenticcqa_raw  (cost=0.00..1256856.62 rows=13859750 width=38) (actual
time=0.110..14342.258rows=13852618 loops=1)
 
              Filter: ((iccqar_ques_code)::text = ANY ('{"DEBRIDEMENT DATE","DEBRIDEMENT THIS VISIT","DEBRIDEMENT
TYPE","DEPTH(CM)","DEPTH DESCRIPTION","DOES PATIENT HAVE PAIN ASSOCIATED WITH THIS WOUND?","DRAIN PRESENT","DRAIN
TYPE","EDGE/ SURROUNDING TISSUE - MACERATION",EDGES,EPITHELIALIZATION,"EXUDATE AMOUNT","EXUDATE TYPE","GRANULATION
TISSUE","INDICATEOTHER TYPE OF WOUND CLOSURE","INDICATE TYPE","INDICATE WOUND CLOSURE","IS THIS A CLOSED SURGICAL WOUND
ORSUSPECTED DEEP TISSUE INJURY?","LENGTH (CM)","MEASUREMENTS TAKEN","NECROTIC TISSUE AMOUNT","NECROTIC TISSUE
TYPE",ODOR,"OTHERCOMMENTS REGARDING DEBRIDEMENT TYPE","OTHER COMMENTS REGARDING DRAIN TYPE","OTHER COMMENTS REGARDING
PAININTERVENTIONS","OTHER COMMENTS REGARDING PAIN QUALITY","OTHER COMMENTS REGARDING REASON MEASUREMENTS NOT
TAKEN","PAINFREQUENCY","PAIN INTERVENTIONS","PAIN QUALITY","PERIPHERAL TISSUE EDEMA","PERIPHERAL TISSUE
INDURATION","REASONMEASUREMENTS NOT TAKEN","RESPONSE TO PAIN INTERVENTIONS",SHAPE,"SIGNS AND SYMPTOMS OF
INFECTION","SKINCOLOR SURROUNDING WOUND",STATE,"SURFACE AREA (SQ CM)","TOTAL NECROTIC TISSUE ESCHAR","TOTAL NECROTIC
TISSUESLOUGH",TUNNELING,"TUNNELING SIZE(CM)/LOCATION - 12 - 3 O''CLOCK","TUNNELING SIZE(CM)/LOCATION - 3 - 6
O''CLOCK","TUNNELINGSIZE(CM)/LOCATION - 6 - 9 O''CLOCK","TUNNELING SIZE(CM)/LOCATION - 9 - 12
O''CLOCK",UNDERMINING,"UNDERMININGSIZE(CM)/LOCATION - 12 - 3 O''CLOCK","UNDERMINING SIZE(CM)/LOCATION - 3 - 6
O''CLOCK","UNDERMININGSIZE(CM)/LOCATION - 6 - 9 O''CLOCK","UNDERMINING SIZE(CM)/LOCATION - 9 - 12 O''CLOCK","WIDTH
(CM)","WOUNDPAIN LEVEL, WHERE 0 = \"NO PAIN\" AND 10 = \"WORST POSSIBLE PAIN\""}'::text[]))
 
              Rows Removed by Filter: 171680
              Buffers: shared read=169851
Settings: effective_cache_size = '52GB', from_collapse_limit = '24', hash_mem_multiplier = '16', jit = 'off',
jit_above_cost= '2e+08', jit_inline_above_cost = '5e+08', jit_optimize_above_cost = '5e+08', join_collapse_limit =
'24',max_parallel_workers = '20', max_parallel_workers_per_gather = '8', random_page_cost = '1.1', temp_buffers =
'4GB',work_mem = ' 2000MB'
 
Planning:
  Buffers: shared hit=186 read=37
Planning Time: 55.709 ms
Execution Time: 1795921.717 ms





-----Original Message-----
From: Peter Geoghegan <pg@bowt.ie> 
Sent: Thursday, July 22, 2021 13:05
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: David Rowley <dgrowleyml@gmail.com>; ldh@laurent-hasson.com; Justin Pryzby <pryzby@telsasoft.com>;
pgsql-performance@postgresql.org
Subject: Re: Big performance slowdown from 11.2 to 13.3

On Thu, Jul 22, 2021 at 9:53 AM Peter Geoghegan <pg@bowt.ie> wrote:
> I suspect David's theory about hash_agg_set_limits()'s ngroup limit is 
> correct. It certainly seems like a good starting point.

I also suspect that if Laurent set work_mem and/or hash_mem_multiplier
*extremely* aggressively, then eventually the hash agg would be in-memory. And without actually using all that much
memory.

I'm not suggesting that that is a sensible resolution to Laurent's complaint. I'm just pointing out that it's probably
notfundamentally impossible to make the hash agg avoid spilling through tuning these GUCs. At least I see no evidence
ofthat right now.
 

--
Peter Geoghegan