Ok, I get that.
Really what I am *rooting* for is Aggregate (and Sort By) Push-Down to FDW
I can already internalize conditional filters for most cases, and doing a count
on the filtered results would be considerably faster in my FDW back-end before
all the records and Datums have to be constructed for postgres to do the
Similarly, I'm very excited about the potential for FDW to advertise a-priori
sort states, so things like external merge-sorts can 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 on them 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
From: Tom Lane [mailto:t...@sss.pgh.pa.us]
Sent: Thursday, February 25, 2016 11:21 PM
To: Gabe F. Rudy <r...@goldenhelix.com>
Subject: Re: [HACKERS] FDW handling count(*) through AnalyzeForeignTable or
other constant time push-down
"Gabe F. Rudy" <r...@goldenhelix.com> writes:
> Is there any way to convince Postgres FDW to leverage the analyze row counts
> or even the "double* totalRowCount" returned from the AcquireSampleRows
> callback from my AnalyzeForeignTable function so that it does not do a
> full-table scan for a COUNT(*) etc?
No. In PG's view, ANALYZE-based row counts are imprecise by definition.
regards, tom lane
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