Re: jsonb Indexing

On 9/20/21 12:52 PM, ramikvl(at)gmail(dot)com wrote:
> Hello Julien,
>
> On 9/17/21 4:00 PM, Julien Rouhaud wrote:
>> Hi,
>>
>> On Fri, Sep 17, 2021 at 9:55 PM <ramikvl(at)gmail(dot)com> 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?

Strangely enough when I re-created the index it's working, now. I
probably made a mistake.

Thank you.