PostgreSQL and BRIN indexes
Test it for yourself. This isn't a problem on a 5 year old laptop with an ssd.
EXPLAIN ANALYZE
CREATE TABLE electrothingy
AS
SELECT
x::int AS id,
(x::int % 20000)::int AS locid, -- fake location ids in the range of 1-20000
now() AS tsin, -- static timestmap
97.5::numeric(5,2) AS temp, -- static temp
x::int AS usage -- usage the same as id not sure what we want here.
FROM generate_series(1,1728000000) -- for 1.7 billion rows
AS gs(x);
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------
Function Scan on generate_series gs (cost=0.00..15.00 rows=1000 width=4) (actual time=173119.796..750391.668 rows=1728000000 loops=1)
Planning time: 0.099 ms
Execution time: 1343954.446 ms
(3 rows)
So it took 22min to create the table. Largely, because the table is a modest 97GB. Next we create the indexes,
CREATE INDEX ON electrothingy USING brin (tsin);
CREATE INDEX ON electrothingy USING brin (id);
VACUUM ANALYZE electrothingy;
It took a good long while to create the indexes too. Though because they're BRIN they're only 2-3 MB and they store easily in ram. Reading 96 GB isn't instantaneous, but it's not a real problem for my laptop at your workload.
Now we query it.
explain analyze
SELECT max(temp)
FROM electrothingy
WHERE id BETWEEN 1000000 AND 1001000;
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=5245.22..5245.23 rows=1 width=7) (actual time=42.317..42.317 rows=1 loops=1)
-> Bitmap Heap Scan on electrothingy (cost=1282.17..5242.73 rows=993 width=7) (actual time=40.619..42.158 rows=1001 loops=1)
Recheck Cond: ((id >= 1000000) AND (id <= 1001000))
Rows Removed by Index Recheck: 16407
Heap Blocks: lossy=128
-> Bitmap Index Scan on electrothingy_id_idx (cost=0.00..1281.93 rows=993 width=0) (actual time=39.769..39.769 rows=1280 loops=1)
Index Cond: ((id >= 1000000) AND (id <= 1001000))
Planning time: 0.238 ms
Execution time: 42.373 ms
(9 rows)
Update with timestamps
Here we generate a table with different timestamps in order to satisify the request to index and search on a timestamp column, creation takes a bit longer because to_timestamp(int) is substantially more slow than now() (which is cached for the transaction)
EXPLAIN ANALYZE
CREATE TABLE electrothingy
AS
SELECT
x::int AS id,
(x::int % 20000)::int AS locid,
-- here we use to_timestamp rather than now(), we
-- this calculates seconds since epoch using the gs(x) as the offset
to_timestamp(x::int) AS tsin,
97.5::numeric(5,2) AS temp,
x::int AS usage
FROM generate_series(1,1728000000)
AS gs(x);
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------
Function Scan on generate_series gs (cost=0.00..17.50 rows=1000 width=4) (actual time=176163.107..5891430.759 rows=1728000000 loops=1)
Planning time: 0.607 ms
Execution time: 7147449.908 ms
(3 rows)
Now we can run a query on a timestamp value instead,,
explain analyze
SELECT count(*), min(temp), max(temp)
FROM electrothingy WHERE tsin BETWEEN '1974-01-01' AND '1974-01-02';
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=296073.83..296073.84 rows=1 width=7) (actual time=83.243..83.243 rows=1 loops=1)
-> Bitmap Heap Scan on electrothingy (cost=2460.86..295490.76 rows=77743 width=7) (actual time=41.466..59.442 rows=86401 loops=1)
Recheck Cond: ((tsin >= '1974-01-01 00:00:00-06'::timestamp with time zone) AND (tsin <= '1974-01-02 00:00:00-06'::timestamp with time zone))
Rows Removed by Index Recheck: 18047
Heap Blocks: lossy=768
-> Bitmap Index Scan on electrothingy_tsin_idx (cost=0.00..2441.43 rows=77743 width=0) (actual time=40.217..40.217 rows=7680 loops=1)
Index Cond: ((tsin >= '1974-01-01 00:00:00-06'::timestamp with time zone) AND (tsin <= '1974-01-02 00:00:00-06'::timestamp with time zone))
Planning time: 0.140 ms
Execution time: 83.321 ms
(9 rows)
Result:
count | min | max
-------+-------+-------
86401 | 97.50 | 97.50
(1 row)
So in 83.321 ms we can aggregate 86,401 records in a table with 1.7 Billion rows. That should be reasonable.
Hour ending
Calculating the hour ending is pretty easy too, truncate the timestamps down and then simply add an hour.
SELECT date_trunc('hour', tsin) + '1 hour' AS tsin,
count(*),
min(temp),
max(temp)
FROM electrothingy
WHERE tsin >= '1974-01-01'
AND tsin < '1974-01-02'
GROUP BY date_trunc('hour', tsin)
ORDER BY 1;
tsin | count | min | max
------------------------+-------+-------+-------
1974-01-01 01:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 02:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 03:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 04:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 05:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 06:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 07:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 08:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 09:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 10:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 11:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 12:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 13:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 14:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 15:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 16:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 17:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 18:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 19:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 20:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 21:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 22:00:00-06 | 3600 | 97.50 | 97.50
1974-01-01 23:00:00-06 | 3600 | 97.50 | 97.50
1974-01-02 00:00:00-06 | 3600 | 97.50 | 97.50
(24 rows)
Time: 116.695 ms
It's important to note, that it's not using an index on the aggregation, though it could. If that's your typically query you probably want a BRIN on date_trunc('hour', tsin) therein lies a small problem in that date_trunc is not immutable so you'd have to first wrap it to make it so.
Partitioning
Another important point of information on PostgreSQL is that PG 10 bring partitioning DDL. So you can, for instance, easily create partitions for every year. Breaking down your modest database into minor ones that are tiny. In doing so, you should be able to use use and maintain btree indexes rather than BRIN which would be even faster.
CREATE TABLE electrothingy_y2016 PARTITION OF electrothingy
FOR VALUES FROM ('2016-01-01') TO ('2017-01-01');
Or whatever.
