I might be out of touch a little with Postgres (I last used it in 2010), but my ... | Hacker News

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mnw21cam on Feb 1, 2021 | parent | context | favorite | on: An unexpected find that freed 20GB of unused index...

I might be out of touch a little with Postgres (I last used it in 2010), but my impression was that COUNT(*) still needed to scan the actual table in order to exclude rows that had been deleted in a transaction, due to the way multi-version concurrency worked. Is this something that has been improved since then?

zeroimpl on Feb 1, 2021 [–]

They support index-only scans now, so there is some sort of optimization which bypasses the table lookup, at least in certain cases.

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