Random note of encouragement

Hey All,

I've been doing some (futile) work trying to speed up aggregates with a
group by in PostgreSQL 9.5.

I installed PostgreSQL 9.6 on the same machine to see if I could get
anything running in parallel when using partitioning - which didn't work.

But - I did find this:

With the following setup:

CREATE TABLE base(
view_time TIMESTAMP WITHOUT time ZONE,
view_time_day TIMESTAMP WITHOUT time ZONE,
count_n numeric);

INSERT INTO base
SELECT view_time,
date_trunc('day', view_time),
COUNT::numeric,
FROM
(SELECT
TIMESTAMP '2015-12-01' + random() * interval '30 days' AS view_time,
trunc(random() * 99 + 1) AS COUNT
FROM generate_series(1,30000000)) a;

analyze base;

Now when I run the following SQL (multiple times to allow for getting
everything into shared buffers, which is 4GB on my machine):

select sum(count_n) from base group by view_time_day;

I get the following results:

PSQL 9.5 - *~21 seconds*
PSQL 9.6 devel - *~8.5 seconds*

I think that's pretty good!

I know this is a devel release, things may change, blah blah. But still,
something has changed for the better here!

I get the same plan on both nodes:

HashAggregate (cost=670590.56..670590.95 rows=31 width=13)
Group Key: view_time_day
-> Seq Scan on base (cost=0.00..520590.04 rows=30000104 width=13)

Cheers,

James Sewell,
PostgreSQL Team Lead / Solutions Architect
______________________________________

Level 2, 50 Queen St, Melbourne VIC 3000

*P *(+61) 3 8370 8000 *W* www.lisasoft.com *F *(+61) 3 8370 8099

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