Postgresql query takes unnecessary (?) long time

I know the web is full of questions, complaints, etc. like my question. But each of them still does not answer the questions of people finding those posts via Google, ... I try to post my question with an example but would like to find some generic advices for possible reasons for this kind of problems. I have a table of this structure (there are some foreign keys) id uuid [uuid_generate_v4()] locationId uuid NULL orderItemId uuid NULL createdAt timestamptz amount numeric(10,4) NULL quantity integer NULL productId uuid NULL bookingId uuid NULL courseId uuid NULL courseUnitId uuid NULL courseModuleId uuid NULL courseCategoryId uuid NULL courseCategoryIds jsonb NULL [[]] kind character varying discountRuleId uuid NULL inquiryId uuid NULL The table is filled with about 3000 rows (which seems not much to me). But when I run this query

* from stat_record

the result is provided after about 20 seconds. If i decrease the number of selected fields (like

id, "locationId from stat_record") the processing time increases linear-relative - I double the amount of selected fields, the waiting time will be doubled also approximately)

What could be potential reasons for this?

 1. Can indizes help in this case? Or are indizes only helping with performance while joining over tables?
 2. Damaged/inconsitent tables? What is a good starting point to learn about VACUUM, INDEX, REINDEX?
 3. ... ?

Execution plan:

explain (analyze, buffers, format text) select * from stat_record``` gives Seq Scan on stat_record (cost=0.00..122.12 rows=3812 width=225) (actual time=0.011..0.636 rows=3812 loops=1) Buffers: shared hit=84 Planning Time: 0.102 ms Execution Time: 0.998 ms