On 27/03/2019 21:54, Darafei "Komяpa" Praliaskouski wrote:
> Hi hackers,
>
> Attached is sketch of small patch that fixes several edge cases with
> autovacuum. Long story short autovacuum never comes to append only
> tables, killing large productions.
>
> First case, mine.
> https://www.postgresql.org/message-id/CAC8Q8tLBeAxR%2BBXWuKK%2BHP5m8tEVYn270CVrDvKXt%3D0PkJTY9g%40mail.gmail.com
>
> We had a table we were appending and wanted Index Only Scan to work. For
> it to work, you need to call VACUUM manually, since VACUUM is the only
> way to mark pages all visible, and autovacuum never comes to append only
> tables. We were clever to invent a workflow without dead tuples and it
> painfully bit us.
>
> Second case, just read in the news.
> https://mailchimp.com/what-we-learned-from-the-recent-mandrill-outage/
>
> Mandrill has 6TB append only table that autovacuum probably never
> vacuumed. Then anti-wraparound came and production went down. If
> autovacuum did its job before that last moment, it would probably be okay.
>
> Idea: look not on dead tuples, but on changes, just like ANALYZE does.
> It's my first patch on Postgres, it's probably all wrong but I hope it
> helps you get the idea.
This was suggested and rejected years ago:
https://www.postgresql.org/message-id/b970f20f-f096-2d3a-6c6d-ee887bd30cfb@2ndquadrant.fr
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