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

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@gmail.com>:
>
>     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@yandex.ru <mailto:padrebolt@yandex.ru>>:
>
>         On 05/06/21 21:15, Alexey M Boltenkov wrote:
>
>             On 05/06/21 19:11, luis.roberto@siscobra.com.br
>             <mailto:luis.roberto@siscobra.com.br> wrote:
>
>                 ----- Mensagem original -----
>
>                     De: "Semen Yefimenko"<semen.yefimenko@gmail.com>
>                     <mailto:semen.yefimenko@gmail.com>
>                     Para: "pgsql-performance"<pgsql-performance@lists.postgresql.org>
>                     <mailto:pgsql-performance@lists.postgresql.org>
>                     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.