5-0-stable: Avoid unscope(:order) when limit_value is presented for countand exists?
#27234
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kamipo
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If `limit_value` is presented, records fetching order is very important for performance. Should not unscope the order in the case.
Records fetching order is very important for performance if `limit` is presented. Should not except the order in the case. And `exists?` replaces select list to `1 AS one` therefore `:distinct` is useless (`DISTINCT 1 AS one`). And PostgreSQL raises the following error if `:distinct` and `:order` are used in the same time. ``` ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list ```
To ease to customize a relation for `exists?`.
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Closing since 5.1 has been released. |
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Backport #26972 and #26981.
Our Rails app encountered lots of slow queries due to except
:orderin production.Currently I'm using
relation.load.sizeinstead as a workaround to keep:order.I'd like to backport these fixes to latest stable branch.