Re: Very poor read performance, query independent

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From: pgsql-performance-owner@xxxxxxxxxxxxxx [mailto:pgsql-performance-owner@xxxxxxxxxxxxxx] On Behalf Of Charles Nadeau
Sent: Wednesday, July 12, 2017 6:05 AM
To: Jeff Janes <jeff.janes@xxxxxxxxx>
Cc: pgsql-performance@xxxxxxxxxxxxxx
Subject: Re: [PERFORM] Very poor read performance, query independent

 

 

flows=# explain (analyze, buffers) SELECT DISTINCT

flows-#    srcaddr,

flows-#    dstaddr,

flows-#    dstport,

flows-#    COUNT(*) AS conversation,

flows-#    SUM(doctets) / 1024 / 1024 AS mbytes 

flows-# FROM

flows-#    flowscompact,

flows-#    mynetworks 

flows-# WHERE

flows-#    mynetworks.ipaddr >>= flowscompact.srcaddr 

flows-#    AND dstaddr IN 

flows-#    (

flows(#       SELECT

flows(#          dstaddr 

flows(#       FROM

flows(#          dstexterne

flows(#    )

flows-# GROUP BY

flows-#    srcaddr,

flows-#    dstaddr,

flows-#    dstport 

flows-# ORDER BY

flows-#    mbytes DESC LIMIT 50;

LOG:  temporary file: path "pg_tblspc/36238/PG_9.6_201608131/pgsql_tmp/pgsql_tmp14573.6", size 1073741824

LOG:  temporary file: path "pg_tblspc/36238/PG_9.6_201608131/pgsql_tmp/pgsql_tmp14573.7", size 1073741824

LOG:  temporary file: path "pg_tblspc/36238/PG_9.6_201608131/pgsql_tmp/pgsql_tmp14573.8", size 639696896

LOG:  duration: 2765020.327 ms  statement: explain (analyze, buffers) SELECT DISTINCT

   srcaddr,

   dstaddr,

   dstport,

   COUNT(*) AS conversation,

   SUM(doctets) / 1024 / 1024 AS mbytes 

FROM

   flowscompact,

   mynetworks 

WHERE

   mynetworks.ipaddr >>= flowscompact.srcaddr 

   AND dstaddr IN 

   (

      SELECT

         dstaddr 

      FROM

         dstexterne

   )

GROUP BY

   srcaddr,

   dstaddr,

   dstport 

ORDER BY

   mbytes DESC LIMIT 50;

                                                                                                              QUERY PLAN                                                                                                              

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

 Limit  (cost=37762321.83..37762321.98 rows=50 width=52) (actual time=2764548.863..2764548.891 rows=50 loops=1)

   Buffers: shared hit=1116590560 read=15851133, temp read=340244 written=340244

   I/O Timings: read=5323746.860

   ->  Unique  (cost=37762321.83..37769053.57 rows=2243913 width=52) (actual time=2764548.861..2764548.882 rows=50 loops=1)

         Buffers: shared hit=1116590560 read=15851133, temp read=340244 written=340244

         I/O Timings: read=5323746.860

         ->  Sort  (cost=37762321.83..37763443.79 rows=2243913 width=52) (actual time=2764548.859..2764548.872 rows=50 loops=1)

               Sort Key: (((sum(flows.doctets) / '1024'::numeric) / '1024'::numeric)) DESC, flows.srcaddr, flows.dstaddr, flows.dstport, (count(*))

               Sort Method: quicksort  Memory: 563150kB

               Buffers: shared hit=1116590560 read=15851133, temp read=340244 written=340244

               I/O Timings: read=5323746.860

               ->  GroupAggregate  (cost=37698151.34..37714980.68 rows=2243913 width=52) (actual time=2696721.610..2752109.551 rows=4691734 loops=1)

                     Group Key: flows.srcaddr, flows.dstaddr, flows.dstport

                     Buffers: shared hit=1116590560 read=15851133, temp read=340244 written=340244

                     I/O Timings: read=5323746.860

                     ->  Sort  (cost=37698151.34..37699273.29 rows=2243913 width=20) (actual time=2696711.428..2732781.705 rows=81896988 loops=1)

                           Sort Key: flows.srcaddr, flows.dstaddr, flows.dstport

                           Sort Method: external merge  Disk: 2721856kB

                           Buffers: shared hit=1116590560 read=15851133, temp read=340244 written=340244

                           I/O Timings: read=5323746.860

                           ->  Gather  (cost=19463936.00..37650810.19 rows=2243913 width=20) (actual time=1777219.713..2590530.887 rows=81896988 loops=1)

                                 Workers Planned: 9

                                 Workers Launched: 9

                                 Buffers: shared hit=1116590559 read=15851133

                                 I/O Timings: read=5323746.860

                                 ->  Hash Semi Join  (cost=19462936.00..37622883.23 rows=249324 width=20) (actual time=1847579.360..2602039.780 rows=8189699 loops=10)

                                       Hash Cond: (flows.dstaddr = flows_1.dstaddr)

                                       Buffers: shared hit=1116588309 read=15851133

                                       I/O Timings: read=5323746.860

                                       ->  Nested Loop  (cost=0.03..18159012.30 rows=249324 width=20) (actual time=1.562..736556.583 rows=45499045 loops=10)

                                             Buffers: shared hit=996551813 read=15851133

                                             I/O Timings: read=5323746.860

                                             ->  Parallel Seq Scan on flows  (cost=0.00..16039759.79 rows=62330930 width=20) (actual time=1.506..547485.066 rows=54155970 loops=10)

                                                   Buffers: shared hit=1634 read=15851133

                                                   I/O Timings: read=5323746.860

                                             ->  Index Only Scan using mynetworks_ipaddr_idx on mynetworks  (cost=0.03..0.03 rows=1 width=8) (actual time=0.002..0.002 rows=1 loops=541559704)

                                                   Index Cond: (ipaddr >>= (flows.srcaddr)::ip4r)

                                                   Heap Fetches: 59971474

                                                   Buffers: shared hit=996550152

                                       ->  Hash  (cost=19462896.74..19462896.74 rows=11210 width=4) (actual time=1847228.894..1847228.894 rows=3099798 loops=10)

                                             Buckets: 4194304 (originally 16384)  Batches: 1 (originally 1)  Memory Usage: 141746kB

                                             Buffers: shared hit=120036496

                                             ->  HashAggregate  (cost=19462829.48..19462863.11 rows=11210 width=4) (actual time=1230049.015..1845955.764 rows=3099798 loops=10)

                                                   Group Key: flows_1.dstaddr

                                                   Buffers: shared hit=120036496

                                                   ->  Nested Loop Anti Join  (cost=0.12..19182620.78 rows=560417390 width=4) (actual time=0.084..831832.333 rows=113420172 loops=10)

                                                         Join Filter: (mynetworks_1.ipaddr >> (flows_1.dstaddr)::ip4r)

                                                         Rows Removed by Join Filter: 453681377

                                                         Buffers: shared hit=120036496

                                                         ->  Index Only Scan using flows_srcaddr_dstaddr_idx on flows flows_1  (cost=0.12..9091067.70 rows=560978368 width=4) (actual time=0.027..113052.437 rows=541559704 loops=10)

                                                               Heap Fetches: 91

                                                               Buffers: shared hit=120036459

                                                         ->  Materialize  (cost=0.00..1.02 rows=4 width=8) (actual time=0.000..0.000 rows=2 loops=5415597040)

                                                               Buffers: shared hit=10

                                                               ->  Seq Scan on mynetworks mynetworks_1  (cost=0.00..1.01 rows=4 width=8) (actual time=0.007..0.008 rows=4 loops=10)

                                                                     Buffers: shared hit=10

 Planning time: 6.689 ms

 Execution time: 2764860.853 ms

(58 rows)

 

Regarding "Also using dstat I can see that iowait time is at about 25%", I don't think the server was doing anything else. If it is important, I can repeat the benchmarks.

Thanks!

 

Charles

 

Charles,

 

In your original posting I couldn’t find what value you set for temp_buffers.

Considering you have plenty of RAM, try setting temp_buffers=’6GB’ and then run ‘explain (analyze, buffers) select…’ in the same session. This should alleviate “disk sort’ problem.

 

Also, could you post the structure of flowscompact, mynetworks, and dstextern tables with all the indexes and number of rows. Actually, are they all – tables, or some of them – views?

 

Igor

 

 

 

 

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