Ok, I get that.
Really what I am *rooting* for is Aggregate (and Sort By) Push-Down to FDW plugins.
I can already internalize conditional filters for most cases, and doing a count on the filtered results would be
considerablyfaster in my FDW back-end before all the records and Datums have to be constructed for postgres to do the
counting.
Similarly, I'm very excited about the potential for FDW to advertise a-priori sort states, so things like external
merge-sortscan pass-through the request for sorted data for fields in which sorting is a no-op in my backend.
Importantly my IDs are sorted by definition since they are essentially array indexes into the column-store, so joining
onthem with merge-sort should be blazing fast, but currently time is wasted sorting these pre-sorted fields.
Just my 2c, and I'll be tracking the 9.6 progress that includes some of these proposals.
Gabe
-----Original Message-----
From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Sent: Thursday, February 25, 2016 11:21 PM
To: Gabe F. Rudy <rudy@goldenhelix.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] FDW handling count(*) through AnalyzeForeignTable or other constant time push-down
"Gabe F. Rudy" <rudy@goldenhelix.com> writes:
> Is there any way to convince Postgres FDW to leverage the analyze row counts or even the "double* totalRowCount"
returnedfrom the AcquireSampleRows callback from my AnalyzeForeignTable function so that it does not do a full-table
scanfor a COUNT(*) etc?
No. In PG's view, ANALYZE-based row counts are imprecise by definition.
regards, tom lane