Simon Riggs wrote:
* We've said here that we
"Don't want hints". If that's what we really think, then this patch must
surely be rejected because its a hint... That isn't my view. I *now*
think we do need hints of various kinds.

cursors_tuple_fraction or OPTIMIZE FOR xxx ROWS isn't the kind of hints we've said "no" to in the past. We don't want hints that work-around planner deficiencies, for example where we get the row count of a node completely wrong. This is different. This is about telling how the application is going to use the result set. It's relevant even assuming that the planner got the estimates spot on. Which plan is the best depends on whether the application can start processing the data as it comes in, or whether it's loading it all in memory first, for example.

  Heikki Linnakangas

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