Re: Bad order by performance (5.7.12 under Aurora)

[Peter Brawley]

Thanks. I think the index would need to be (id,ultima_elaborazione) to be usable.

Left Joins tend to force full table scans so they make for performance trouble. Some of them look to me as if they might be behaving like Inner Joins, others look translatable to Semi-joins, but I'd need a bit of example data to test that out, and to try 8.0 optimisations.

What does the first row of Explain say without the Order By clause?

On 5.7 the query cache is deprecated but still available. If it's on, it may be hiding worse performance, to find out, turn it off (in 8.0 it's removed).



Edited 1 time(s). Last edit at 11/26/2019 05:01PM by Peter Brawley.