Re: [Proposal] Table partition + join pushdown

On Mon, Jan 25, 2016 at 9:09 PM, Kouhei Kaigai <kaigai@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
partitioning:

http://www.postgresql.org/message-id/CA+Tgmob2wfJivFoCDLuUnovJsFTp6QsqxiPpxvNNoGLY+3rjbg@mail.gmail.com

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