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Re: jsonb Indexing

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Hello Julien,

On 9/17/21 4:00 PM, Julien Rouhaud wrote:
Hi,

On Fri, Sep 17, 2021 at 9:55 PM <ramikvl@xxxxxxxxx> wrote:
I was wondering what I'm doing wrong. There are steps what I've tried:

CREATE TABLE api (
      jdoc jsonb
);

INSERT INTO api (jdoc)
      VALUES ('{
      "guid": "9c36adc1-7fb5-4d5b-83b4-90356a46061a",
      "name": "Angela Barton",
      "is_active": true,
      "company": "Magnafone",
      "address": "178 Howard Place, Gulf, Washington, 702",
      "registered": "2009-11-07T08:53:22 +08:00",
      "latitude": 19.793713,
      "longitude": 86.513373,
      "tags": [
          "enim",
          "aliquip",
          "qui"
      ]
}');

CREATE INDEX idxgintags ON api USING GIN ((jdoc->'tags'));

EXPLAIN ANALYZE SELECT jdoc->'guid', jdoc->'name' FROM api WHERE jdoc ->
'tags' ? 'qui';

And the result is

Seq Scan on api  (cost=0.00..1.02 rows=1 width=64) (actual
time=0.019..0.021 rows=1 loops=1)
    Filter: ((jdoc -> 'tags'::text) ? 'qui'::text)

Planning Time: 0.115 ms

Execution Time: 0.047 ms

Do you know why Index Scan on idxgintag is not used?
Yes, because doing an index scan on a table containing a single row is
an order or magnitude less efficient than simply doing a sequential
scan.  You should try to simulate something close to your production
data to see something interesting.

Thank you for the tip. I've tried to generate more data. I have 2000 rows in the table but the query still uses sequential scan.

Seq Scan on api  (cost=0.00..131.00 rows=2000 width=64) (actual time=0.005..0.959 rows=2000 loops=1)
  Filter: ((jdoc -> 'tags'::text) ? 'qui'::text)
Planning Time: 0.064 ms
Execution Time: 1.027 ms

Any thoughts?






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