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* Request to help on Query improvement suggestion.
@ 2020-05-22 10:45 devchef2020 d <devchef2020@gmail.com>
0 siblings, 1 reply; 3+ messages in thread
From: devchef2020 d @ 2020-05-22 10:45 UTC (permalink / raw)
To: pgsql-admin@postgresql.org; pgsql-general@postgresql.org; pgsql-performance
Hi Team,
Thanks for your support.
Could someone please suggest on the below query.
One of the query which was created on GIS data is taking a long time and
even it is not taking the index as well. I have included all the required
details for reference.
Database Stack:
===============
PostgreSQL : 9.5.15
Postgis: 2.2.7
Table Structure:
===================
ALTER TABLE SCHEMA.TABLE_NAME ADD COLUMN parental_path text;
Created Indexes on column parental_path:
=================================
CREATE INDEX cable_pair_parental_path_idx
ON SCHEMA.TABLE_NAME
USING btree
(md5(parental_path) COLLATE pg_catalog."default");
CREATE INDEX cable_pair_parental_path_idx_fulltext
ON SCHEMA.TABLE_NAME
USING gist
(parental_path COLLATE pg_catalog."default");
Sample data in "parental_path" column:
======================================
'route--2309421/2951584/3373649/2511322/1915187/2696397/2623291/2420708/2144348/2294454,circuit--88458/88460,sheath--8874'
Actual Query:
=============
SELECT seq_no + 1 FROM SCHEMA.TABLE_NAME WHERE (parental_path LIKE
'%,sheath--' || cable_seq_id || ',%' OR parental_path LIKE 'sheath--' ||
cable_seq_id || ',%' OR parental_path LIKE '%,sheath--' || cable_seq_id OR
parental_path = 'sheath--' || cable_seq_id) ORDER BY seq_no DESC LIMIT 1;
Explain Plan:
=============
Limit (cost=108111.60..108111.61 rows=1 width=4) (actual
time=4597.605..4597.605 rows=0 loops=1)
Output: ((seq_no + 1)), seq_no
Buffers: shared hit=2967 read=69606 dirtied=1
-> Sort (cost=108111.60..108113.09 rows=595 width=4) (actual
time=4597.603..4597.603 rows=0 loops=1)
Output: ((seq_no + 1)), seq_no
Sort Key: TABLE_NAME.seq_no DESC
Sort Method: quicksort Memory: 25kB
Buffers: shared hit=2967 read=69606 dirtied=1
-> *Seq Scan on SCHEMA.TABLE_NAME (cost=0.00..108108.63 rows=595
width=4) (actual time=4597.595..4597.595 rows=0 loops=1)*
Output: (seq_no + 1), seq_no
Filter: ((TABLE_NAME.parental_path ~~
'%,sheath--64690,%'::text) OR (TABLE_NAME.parental_path ~~
'sheath--64690,%'::text) OR (TABLE_NAME.parental_path ~~
'%,sheath--64690'::text) OR (TABLE_NAME.parental_path =
'sheath--64690'::text))
Rows Removed by Filter: 1930188
Buffers: shared hit=2967 read=69606 dirtied=1
Please share your suggestion.
Thanks & Regards,
Devchef.
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Request to help on Query improvement suggestion.
@ 2020-05-25 06:47 Laurenz Albe <laurenz.albe@cybertec.at>
parent: devchef2020 d <devchef2020@gmail.com>
0 siblings, 0 replies; 3+ messages in thread
From: Laurenz Albe @ 2020-05-25 06:47 UTC (permalink / raw)
To: devchef2020 d <devchef2020@gmail.com>; pgsql-admin@postgresql.org; pgsql-general@postgresql.org; pgsql-performance
On Fri, 2020-05-22 at 16:15 +0530, devchef2020 d wrote:
> PostgreSQL : 9.5.15
> Created Indexes on column parental_path:
> =================================
>
> CREATE INDEX cable_pair_parental_path_idx
> ON SCHEMA.TABLE_NAME
> USING btree
> (md5(parental_path) COLLATE pg_catalog."default");
>
> CREATE INDEX cable_pair_parental_path_idx_fulltext
> ON SCHEMA.TABLE_NAME
> USING gist
> (parental_path COLLATE pg_catalog."default");
> SELECT seq_no + 1 FROM SCHEMA.TABLE_NAME WHERE (parental_path LIKE '%,sheath--' || cable_seq_id || ',%' OR parental_path LIKE 'sheath--' || cable_seq_id || ',%' OR parental_path LIKE '%,sheath--' ||
> cable_seq_id OR parental_path = 'sheath--' || cable_seq_id) ORDER BY seq_no DESC LIMIT 1;
>
> Explain Plan:
> =============
>
> Limit (cost=108111.60..108111.61 rows=1 width=4) (actual time=4597.605..4597.605 rows=0 loops=1)
> Output: ((seq_no + 1)), seq_no
> Buffers: shared hit=2967 read=69606 dirtied=1
> -> Sort (cost=108111.60..108113.09 rows=595 width=4) (actual time=4597.603..4597.603 rows=0 loops=1)
> Output: ((seq_no + 1)), seq_no
> Sort Key: TABLE_NAME.seq_no DESC
> Sort Method: quicksort Memory: 25kB
> Buffers: shared hit=2967 read=69606 dirtied=1
> -> Seq Scan on SCHEMA.TABLE_NAME (cost=0.00..108108.63 rows=595 width=4) (actual time=4597.595..4597.595 rows=0 loops=1)
> Output: (seq_no + 1), seq_no
> Filter: ((TABLE_NAME.parental_path ~~ '%,sheath--64690,%'::text) OR (TABLE_NAME.parental_path ~~ 'sheath--64690,%'::text) OR (TABLE_NAME.parental_path ~~ '%,sheath--64690'::text) OR
> (TABLE_NAME.parental_path = 'sheath--64690'::text))
> Rows Removed by Filter: 1930188
> Buffers: shared hit=2967 read=69606 dirtied=1
An index on an expression can only be used if the expression is exactly the same as on one
side of an operator in a WHERE condition.
So your only chance with that query is to hope for a bitmap OR with an index on "parental path".
Two things to try:
1) CREATE INDEX ON table_name (parental_path text_pattern_ops);
2) CREATE EXTENSION pg_trgm;
CREATE INDEX ON table_name USING GIN (parental_path gin_trgm_ops);
Yours,
Laurenz Albe
--
Cybertec | https://www.cybertec-postgresql.com
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2020-05-22 10:45 Request to help on Query improvement suggestion. devchef2020 d <devchef2020@gmail.com>
2020-05-25 06:47 ` Laurenz Albe <laurenz.albe@cybertec.at>
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