Re: Very slow Query compared to Oracle / SQL - Server

[Alexey M Boltenkov <padrebolt@xxxxxxxxx>]

On 05/06/21 22:58, Alexey M Boltenkov wrote:

Have you try of excluding not null from index? Can you give dispersion of archivestatus?

06.05.2021, 21:59, "Semen Yefimenko" <semen.yefimenko@xxxxxxxxx>:

Yes, rewriting the query with an IN clause was also my first approach, but I didn't help much. 
The Query plan did change a little bit but the performance was not impacted.

CREATE INDEX idx_arcstatus_le1 ON schema.logtable ( archivestatus ) where (archivestatus <= 1)

ANALYZE  schema.logtable

This resulted in this query plan:

Gather Merge  (cost=344618.96..394086.05 rows=423974 width=2549) (actual time=7327.777..9142.358 rows=516031 loops=1)

  Output: column1, .. , column54

  Workers Planned: 2

  Workers Launched: 2

  Buffers: shared hit=179817 read=115290

  ->  Sort  (cost=343618.94..344148.91 rows=211987 width=2549) (actual time=7258.314..7476.733 rows=172010 loops=3)

        Output: column1, .. , column54

        Sort Key: logtable.timestampcol DESC

        Sort Method: quicksort  Memory: 64730kB

        Worker 0:  Sort Method: quicksort  Memory: 55742kB

        Worker 1:  Sort Method: quicksort  Memory: 55565kB

        Buffers: shared hit=179817 read=115290

        Worker 0: actual time=7231.774..7458.703 rows=161723 loops=1

          Buffers: shared hit=55925 read=36265

        Worker 1: actual time=7217.856..7425.754 rows=161990 loops=1

          Buffers: shared hit=56197 read=36242

        ->  Parallel Bitmap Heap Scan on schema.logtable  (cost=5586.50..324864.86 rows=211987 width=2549) (actual time=1073.266..6805.850 rows=172010 loops=3)

              Output: column1, .. , column54

              Recheck Cond: ((logtable.entrytype = 4000) OR (logtable.entrytype = 4001) OR (logtable.entrytype = 4002))

              Filter: (logtable.archivestatus <= 1)

              Heap Blocks: exact=109146

              Buffers: shared hit=179803 read=115290

              Worker 0: actual time=1049.875..6809.231 rows=161723 loops=1

                Buffers: shared hit=55918 read=36265

              Worker 1: actual time=1035.156..6788.037 rows=161990 loops=1

                Buffers: shared hit=56190 read=36242

              ->  BitmapOr  (cost=5586.50..5586.50 rows=514483 width=0) (actual time=945.179..945.179 rows=0 loops=1)

                    Buffers: shared hit=3 read=1329

                    ->  Bitmap Index Scan on idx_entrytype  (cost=0.00..738.13 rows=72893 width=0) (actual time=147.915..147.916 rows=65970 loops=1)

                          Index Cond: (logtable.entrytype = 4000)

                          Buffers: shared hit=1 read=171

                    ->  Bitmap Index Scan on idx_entrytype  (cost=0.00..2326.17 rows=229965 width=0) (actual time=473.450..473.451 rows=225040 loops=1)

                          Index Cond: (logtable.entrytype = 4001)

                          Buffers: shared hit=1 read=579

                    ->  Bitmap Index Scan on idx_entrytype  (cost=0.00..2140.61 rows=211624 width=0) (actual time=323.801..323.802 rows=225021 loops=1)

                          Index Cond: (logtable.entrytype = 4002)

                          Buffers: shared hit=1 read=579

Settings: random_page_cost = '1', search_path = '"$user", schema, public', temp_buffers = '80MB', work_mem = '1GB'

Planning Time: 0.810 ms

Execution Time: 9647.406 ms

seemingly faster.
After doing a few selects, I reran ANALYZE:
Now it's even faster, probably due to cache and other mechanisms.

Gather Merge  (cost=342639.19..391676.44 rows=420290 width=2542) (actual time=2944.803..4534.725 rows=516035 loops=1)

  Output: column1, .. , column54

  Workers Planned: 2

  Workers Launched: 2

  Buffers: shared hit=147334 read=147776

  ->  Sort  (cost=341639.16..342164.53 rows=210145 width=2542) (actual time=2827.256..3013.960 rows=172012 loops=3)

        Output: column1, .. , column54

        Sort Key: logtable.timestampcol DESC

        Sort Method: quicksort  Memory: 71565kB

        Worker 0:  Sort Method: quicksort  Memory: 52916kB

        Worker 1:  Sort Method: quicksort  Memory: 51556kB

        Buffers: shared hit=147334 read=147776

        Worker 0: actual time=2771.975..2948.928 rows=153292 loops=1

          Buffers: shared hit=43227 read=43808

        Worker 1: actual time=2767.752..2938.688 rows=148424 loops=1

          Buffers: shared hit=42246 read=42002

        ->  Parallel Bitmap Heap Scan on schema.logtable  (cost=5537.95..323061.27 rows=210145 width=2542) (actual time=276.401..2418.925 rows=172012 loops=3)

              Output: column1, .. , column54

              Recheck Cond: ((logtable.entrytype = 4000) OR (logtable.entrytype = 4001) OR (logtable.entrytype = 4002))

              Filter: (logtable.archivestatus <= 1)

              Heap Blocks: exact=122495

              Buffers: shared hit=147320 read=147776

              Worker 0: actual time=227.701..2408.580 rows=153292 loops=1

                Buffers: shared hit=43220 read=43808

              Worker 1: actual time=225.996..2408.705 rows=148424 loops=1

                Buffers: shared hit=42239 read=42002

              ->  BitmapOr  (cost=5537.95..5537.95 rows=509918 width=0) (actual time=203.940..203.941 rows=0 loops=1)

                    Buffers: shared hit=1332

                    ->  Bitmap Index Scan on idx_entrytype  (cost=0.00..680.48 rows=67206 width=0) (actual time=31.155..31.156 rows=65970 loops=1)

                          Index Cond: (logtable.entrytype = 4000)

                          Buffers: shared hit=172

                    ->  Bitmap Index Scan on idx_entrytype  (cost=0.00..2220.50 rows=219476 width=0) (actual time=112.459..112.461 rows=225042 loops=1)

                          Index Cond: (logtable.entrytype = 4001)

                          Buffers: shared hit=580

                    ->  Bitmap Index Scan on idx_entrytype  (cost=0.00..2258.70 rows=223236 width=0) (actual time=60.313..60.314 rows=225023 loops=1)

                          Index Cond: (logtable.entrytype = 4002)

                          Buffers: shared hit=580

Settings: random_page_cost = '1', search_path = '"$user", schema, public', temp_buffers = '80MB', work_mem = '1GB'

Planning Time: 0.609 ms

Execution Time: 4984.490 ms

I don't see the new index used but it seems it's boosting the performance nevertheless.
I kept the query, so I didn't rewrite the query to be WITHOUT nulls. 
Thank you already for the hint. What else can I do? With the current parameters, the query finishes in about 3.9-5.2 seconds which is already much better but still nowhere near the speeds of 280 ms in oracle.
I would love to get it to at least 1 second.  

Am Do., 6. Mai 2021 um 20:20 Uhr schrieb Alexey M Boltenkov <padrebolt@xxxxxxxxx>:

On 05/06/21 21:15, Alexey M Boltenkov wrote:

On 05/06/21 19:11, luis.roberto@xxxxxxxxxxxxxxx wrote:

----- Mensagem original -----

De: "Semen Yefimenko" <semen.yefimenko@xxxxxxxxx>
Para: "pgsql-performance" <pgsql-performance@xxxxxxxxxxxxxxxxxxxx>
Enviadas: Quinta-feira, 6 de maio de 2021 11:38:39
Assunto: Very slow Query compared to Oracle / SQL - Server

SELECT column1,..., column54 where ((entrytype = 4000 or entrytype = 4001 or
entrytype = 4002) and (archivestatus <= 1)) order by timestampcol desc;

 

The first thing I would try is rewriting the query to:

SELECT column1,..., column54 
  FROM logtable
 WHERE (entrytype in (4000,4001,4002)) 
   AND (archivestatus <= 1)) 
 ORDER BY timestampcol DESC;

Check if that makes a difference...

Luis R. Weck 

The IN statement will probable result in just recheck condition change to entrytype = any('{a,b,c}'::int[]). Looks like dispersion of archivestatus is not enough to use index idx_arcstatus.

Please try to create partial index with condition like (archivestatus <= 1) and rewrite select to use (archivestatus is not null and archivestatus <= 1).

CREATE INDEX idx_arcstatus_le1 ON schema.logtable ( archivestatus ) where (archivestatus <= 1) TABLESPACE tablespace;

I'm sorry, 'archivestatus is not null' is only necessary for index without nulls.

CREATE INDEX idx_arcstatus_le1 ON schema.logtable ( archivestatus ) where (archivestatus is not null and archivestatus <= 1) TABLESPACE tablespace;

BTW, please try to reset random_page_cost.