Query too slow in Postgresql in table with > 12M rows - postgresql

Question

I have a simple table with more than 12 Million rows growing every time, in my web app.
+-----+-----+------+-------+--------+
| id | dtt | cus | event | server |
-------------------------------------
I'm getting the count of today events by customer using this query
SELECT COUNT(*) FROM events
WHERE dtt AT TIME ZONE 'America/Santiago' >=date(now() AT TIME ZONE 'America/Santiago') + interval '1s'
AND cus=2
And the performance is very bad for my web app : 22702 ms.
"Aggregate (cost=685814.54..685814.55 rows=1 width=0) (actual time=21773.451..21773.452 rows=1 loops=1)"
" -> Seq Scan on events (cost=0.00..675644.52 rows=4068008 width=0) (actual time=10277.508..21732.548 rows=409808 loops=1)"
" Filter: ((cus = 2) AND (timezone('America/Santiago'::text, dtt) >= (date(timezone('America/Santiago'::text, now())) + '00:00:01'::interval)))"
" Rows Removed by Filter: 12077798"
"Planning time: 0.127 ms"
"Execution time: 21773.509 ms"
I have the next Indexes created:
CREATE INDEX events_dtt_idx
ON events
USING btree
(dtt);
CREATE INDEX events_id_desc
ON events
USING btree
(id DESC NULLS LAST);
CREATE INDEX events_cus_idx
ON events
USING btree
(cus);
CREATE INDEX events_id_idx
ON events
USING btree
(id);
Using Postgresql 9.4, Linux x64
How can I improve that? Thanks in advance.

Answer 1

something like:
CREATE INDEX dtt_tz_idx ON events (DATE(dtt AT TIME ZONE 'America/Santiago'));
then query
SELECT COUNT(*) FROM events
WHERE DATE(TIMEZONE('America/Santiago'::text, dtt)) >=date(now() AT TIME ZONE 'America/Santiago') + interval '1s'
AND cus=2
If it doesn't work, try "\d dtt_tz_idx" in psql and try to match the datatypes on your query with the index.

Answer 2

Finally I could fix the problem with that index:
CREATE INDEX dtt_tz_idx ON events (TIMEZONE('America/Santiago'::text, dtt));
Thanks sivan & vyegorov for your guide, now the plan is:
"Aggregate (cost=567240.43..567240.44 rows=1 width=0) (actual time=238.440..238.440 rows=1 loops=1)"
" -> Bitmap Heap Scan on events (cost=82620.28..556463.97 rows=4310584 width=0) (actual time=41.445..208.870 rows=344453 loops=1)"
" Recheck Cond: (timezone('America/Santiago'::text, dtt) >= (date(timezone('America/Santiago'::text, now())) + '00:00:01'::interval))"
" Filter: (cus = 2)"
" Rows Removed by Filter: 9433"
" Heap Blocks: exact=9426"
" -> Bitmap Index Scan on dtt_tz_idx (cost=0.00..81542.63 rows=4415225 width=0) (actual time=38.866..38.866 rows=353886 loops=1)"
" Index Cond: (timezone('America/Santiago'::text, dtt) >= (date(timezone('America/Santiago'::text, now())) + '00:00:01'::interval))"
"Planning time: 0.221 ms"
"Execution time: 238.509 ms"