Postgres not using index on views - Mailing list pgsql-performance

Hi,

I am seeing a performance problem with postgresql v 11.7 on views, and I am wondering if anyone can tell me why or has any suggestion.

A table is created as:

CREATE TABLE "FBNK_CUSTOMER" (RECID VARCHAR(255) NOT NULL PRIMARY KEY, XMLRECORD VARCHAR)

And contains only 180 rows.

Doing an explain plan on the view created over this gives:

EXPLAIN ANALYZE

select RECID from "V_FBNK_CUSTOMER"

Subquery Scan on "V_FBNK_CUSTOMER"  (cost=0.00..19014.60 rows=180 width=7) (actual time=459.601..78642.189 rows=180 loops=1)

  ->  Seq Scan on "FBNK_CUSTOMER" a  (cost=0.00..19012.80 rows=180 width=14575) (actual time=459.600..78641.950 rows=180 loops=1)

Planning Time: 0.679 ms

Execution Time: 78642.616 ms

Yet an Explain plan on the underlying table( on select RECID from “FBNK_CUSTOMER”) gives:

Seq Scan on "FBNK_CUSTOMER"  (cost=0.00..22.80 rows=180 width=7) (actual time=0.004..0.272 rows=180 loops=1)

Planning Time: 0.031 ms

Execution Time: 0.288 ms

So you can see that postgresql is not using the primary key index for RECID.  THIS IS NOT THE CASE FOR ORACLE where the primary key index is used in the explain plan

The view is created similar to the following where extractValueJS is a stored procedure that extracts a value from the VARCHAR XMLRECORD column.

CREATE VIEW "V_FBNK_CUSTOMER" as

SELECT a.RECID, a.XMLRECORD "THE_RECORD"

,a.RECID "CUSTOMER_CODE"

,a.RECID "CUSTOMER_NO"

,extractValueJS(a.XMLRECORD, 1, 0) "MNEMONIC"

,extractValueJS(a.XMLRECORD, 2, 0) "SHORT_NAME"

,extractValueJS(a.XMLRECORD, 2, -1) "SHORT_NAME_2"

, etc

, extractValueJS(a.XMLRECORD, 179, 9) "TESTER"

FROM

"FBNK_CUSTOMER" a

As well, the problem gets worse as columns are added to the view, irrespective of the SELECTION columns and it seems to perform some activity behind.

Creating an empty view,

CREATE VIEW "V_FBNK_CUSTOMER_TEST" as

SELECT a.RECID, a.XMLRECORD "THE_RECORD"

,a.RECID "CUSTOMER_CODE"

,a.RECID "CUSTOMER_NO"

FROM

"FBNK_CUSTOMER" a                ------------- > 3 ms   select RECID from "V_FBNK_CUSTOMER_TEST"           

CREATE VIEW "V_FBNK_CUSTOMER_TEST" as

SELECT a.RECID, a.XMLRECORD "THE_RECORD"

,a.RECID "CUSTOMER_CODE"

,a.RECID "CUSTOMER_NO"

,extractValueJS(a.XMLRECORD, 1, 0) "MNEMONIC"

FROM

"FBNK_CUSTOMER" a               ----------------à 54 ms select RECID from "V_FBNK_CUSTOMER_TEST"

CREATE VIEW "V_FBNK_CUSTOMER_TEST" as

SELECT a.RECID, a.XMLRECORD "THE_RECORD"

,a.RECID "CUSTOMER_CODE"

,a.RECID "CUSTOMER_NO"

,extractValueJS(a.XMLRECORD, 1, 0) "MNEMONIC"

,extractValueJS(a.XMLRECORD, 2, 0) "SHORT_NAME"

FROM

"FBNK_CUSTOMER" a             ----------------------à 118 ms select RECID from "V_FBNK_CUSTOMER_TEST"

The following query takes an extremely long time for only 180 rows, and what this means is that we would have to index anything appearing in the where clause for every table in order to use views because the views seem not to consider the select clause.  Why is that and does anyone know a way around this?

SELECT RECID FROM "V_FBNK_CUSTOMER" WHERE "TESTER" = '5.00' ORDER BY RECID

Sort  (cost=19015.06..19015.06 rows=1 width=7) (actual time=102172.500..102172.501 rows=1 loops=1)

  Sort Key: "V_FBNK_CUSTOMER".recid

  Sort Method: quicksort  Memory: 25kB

  ->  Subquery Scan on "V_FBNK_CUSTOMER"  (cost=0.00..19015.05 rows=1 width=7) (actual time=91242.866..102172.474 rows=1 loops=1)

        Filter: (("V_FBNK_CUSTOMER"."TESTER")::text = '5.00'::text)

        Rows Removed by Filter: 179

        ->  Seq Scan on "FBNK_CUSTOMER" a  (cost=0.00..19012.80 rows=180 width=14575) (actual time=613.455..102172.175 rows=180 loops=1)

Planning Time: 1.674 ms

Execution Time: 102174.015 ms