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

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(at)yandex(dot)ru>:

> On 05/06/21 21:15, Alexey M Boltenkov wrote:
>
> On 05/06/21 19:11, luis(dot)roberto(at)siscobra(dot)com(dot)br wrote:
>
> ----- Mensagem original -----
>
> De: "Semen Yefimenko" <semen(dot)yefimenko(at)gmail(dot)com> <semen(dot)yefimenko(at)gmail(dot)com>
> Para: "pgsql-performance" <pgsql-performance(at)lists(dot)postgresql(dot)org> <pgsql-performance(at)lists(dot)postgresql(dot)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;
>