Now the query:
explain (verbose, buffers, analyze)
with last_table_ids as materialized(
select xx from (
select LAST_VALUE(pk_id) over (partition by integer_field_2 order by
datetime_field_1 RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED
FOLLOWING) xx
from test_table
where integer_field_1 = 1
and datetime_field_1 <= CURRENT_TIMESTAMP
) ww group by ww.xx
),
last_row_per_ids as (
select tt.* from last_table_ids lt
inner join test_table tt on (tt.pk_id = lt.xx)
)
select * /* or count(*) */ from last_row_per_ids;
This query, on my PC, takes 46 seconds!!!
(Away from laptop and using my phone)
Something like:
select distinct on (integer_field_2) * from test_table where integer_field_1 = 1 and datetime_field_1 <= CURRENT_TIMESTAMP order by integer_field_2,datetime_field_1 desc;
Might run a bit faster. However if it's slow due to I/O then maybe not much faster. Your version took about 5 seconds on my phone and my version ran in 1.5 seconds.
It's difficult for me to check the results match with each query from my phone. A quick scan of the first 10 or so records looked good.
If the updated query is still too slow on cold cache then faster disks might be needed.
David