On Mon, Jan 25, 2016 at 9:09 PM, Kouhei Kaigai <kai...@ak.jp.nec.com> wrote:
> Of course, its implementation is not graceful enough, especially, above
> point because this extra filter will change expected number of rows to
> be produced by inner relation, and relevant cost.
> Right now, his patch calls cost_seqscan() and others according to the
> type of inner relation by itself. Of course, it is not a portable way,
> if inner relation would not be a simple relations scan.
> Due to path construction staging, AppendPath with underlying join paths
> has to be constructed on join path investigation steps. So, what is the
> reasonable way to make inner relation's path node with filters pushed-
> down?
> It is the most ugly part of the current patch.

I think that it needs to be done only in contexts where we can
guarantee that the optimization is correct, like declarative hash


As I said upthread, in general your proposal will not work and will
lead to wrong answers to queries.

Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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