Re: EXPLAIN (ANALYZE, BUFFERS) - puzzling numbers for a simple query.

> Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> writes:

> > "generate_series" has a support function from v12 on:

> True, but I don't think it can do anything with non-constant inputs,
> as we have in the OP's case.

As confirmed by this:

https://dbfiddle.uk/?rdbms=postgres_12&fiddle=d0b70717faca3b094be8b4a096758b94

Plan:

==============
Sort (cost=623.22..640.72 rows=7000 width=10) (actual
time=0.067..0.070 rows=42 loops=1)
Sort Key: id, (((generate_series((start_date)::timestamp with time
zone, (end_date)::timestamp with time zone, '1
day'::interval)))::date)
Sort Method: quicksort Memory: 26kB
Buffers: shared hit=1
-> Result (cost=0.00..176.16 rows=7000 width=10) (actual
time=0.014..0.045 rows=42 loops=1)
Buffers: shared hit=1
-> ProjectSet (cost=0.00..36.16 rows=7000 width=14) (actual
time=0.013..0.033 rows=42 loops=1)
CUT
==============

It goes for the full 7,000 even after a VACUUM FULL VERBOSE ANALYZE test;

Pól...

> regards, tom lane