Postgres does not use an index with "ORDER BY"

Question

• I have a very large table.
• I have an index in col1 columns.
• I would like to get data sorted by col1.
• From the query plan, I can say that it does not use an index.
• When I add "LIMIT", it starts using the index
• For a large value for "LIMIT" it stops using the index.

Any clue?

PS I would like to get data grouped by col1 values ​​(not necessarily sorted), any sentences other than "ORDER BY".

THANK!!

Answer 1

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set enable_seqscan = false

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Edit
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Answer 2

a_horse_with_no_name:

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