Improving performance of query - postgresql

Question

We have a PostgreSQL query with multiple tables and left outer joins, and is running very slow.
It is completing in 25-40s, so we want to optimize it more and want to decrease run time to 1-2 sec.
select a.campaignid, b.campaign_name , case when b.message_type_id = 1 then 'Promotional'
when b.message_type_id = 2 then 'Transactional'
else 'Other' end as Campaign_type, c.username , aggregator_type,
e.cli_manager_id as senderID,
b.schedule_time as campaign_schedule_date,
count(a.mobile) as campaign_submitted_count, count(case when a.status = 'DELIVRD' then mobile end) as Delivered,
count(a.mobile) as Total_count,
count(case when a.status = 'FAILED' then mobile end) as failure_count,
count(case when a.status = 'DND_check_failed' then mobile end) as DND_count,
sum(credits_used) as credits_used
from tbl_cdr_test a left outer join tbl_campaign b
on a.campaignid = b.tbl_campaign_id left outer join tbl_users_master c
on b.user_id =c.user_master_id
left outer join tbl_cli_manager e on b.user_id = e.user_id
left outer join tbl_user_channel f on b.user_id =f.user_id
left outer join tbl_user_configurations g on b.user_id = g.user_id
where date(insert_datetime) between '2020-05-23' and '2020-06-23'
and c.username = coalesce(null, c.username)
and g.msg_cat_id = coalesce(null, g.msg_cat_id)
and a.campaignid = coalesce(null, a.campaignid)
and e.cli_manager_id = coalesce(null, e.cli_manager_id)
group by a.campaignid, b.campaign_name , b.message_type_id,c.username , b.schedule_time,
aggregator_type, e.cli_manager_id;
We have create appropriate indexes as well, but still it is taking time.
Moreover there is "external merge disk" sorting method in execution plan whereas to resolve same I have set work_mem = 50MB. Still it is using disk sort instead of memory.Please suggest
Below is execution plan:
GroupAggregate (cost=4872.01..4872.07 rows=1 width=543) (actual time=20564.239..27415.264 rows=8 loops=1)
Group Key: a.campaignid, b.campaign_name, b.message_type_id, c.username, b.schedule_time, f.aggregator_type, e.cli_manager_id
-> Sort (cost=4872.01..4872.01 rows=1 width=483) (actual time=19627.424..25020.702 rows=3206196 loops=1)
Sort Key: a.campaignid, b.campaign_name, b.message_type_id, c.username, b.schedule_time, f.aggregator_type, e.cli_manager_id
Sort Method: external merge Disk: 281456kB
-> Nested Loop (cost=22.03..4872.00 rows=1 width=483) (actual time=99.704..12086.244 rows=3206196 loops=1)
Join Filter: (b.user_id = g.user_id)
-> Nested Loop Left Join (cost=21.89..4871.79 rows=1 width=495) (actual time=99.688..4518.533 rows=3206196 loops=1)
-> Nested Loop (cost=21.75..4871.54 rows=1 width=77) (actual time=99.664..935.689 rows=356244 loops=1)
-> Nested Loop (cost=21.33..31.57 rows=1 width=65) (actual time=0.295..2.376 rows=588 loops=1)
Join Filter: (b.user_id = c.user_master_id)
-> Merge Join (cost=21.18..30.22 rows=6 width=46) (actual time=0.246..0.663 rows=588 loops=1)
Merge Cond: (e.user_id = b.user_id)
-> Index Scan using "idx_FK_7hc6agd_tbl_cli_ma_1592228110_32" on tbl_cli_manager e (cost=0.42..6281.84 rows=762 width=12) (actual time=0.014..0.035 rows=5 loops=1)
Filter: (cli_manager_id = COALESCE(cli_manager_id))
-> Sort (cost=20.76..21.13 rows=147 width=34) (actual time=0.225..0.333 rows=585 loops=1)
Sort Key: b.user_id
Sort Method: quicksort Memory: 36kB
-> Seq Scan on tbl_campaign b (cost=0.00..15.47 rows=147 width=34) (actual time=0.013..0.154 rows=147 loops=1)
-> Index Scan using ind_user_master_c_user on tbl_users_master c (cost=0.14..0.21 rows=1 width=19) (actual time=0.002..0.002 rows=1 loops=588)
Index Cond: (user_master_id = e.user_id)
Filter: ((username)::text = (COALESCE(username))::text)
-> Append (cost=0.42..4839.94 rows=3 width=20) (actual time=0.546..1.426 rows=606 loops=588)
-> Index Scan using testh11_campaignid_idx on testh11 a (cost=0.42..4253.99 rows=2 width=20) (actual time=0.543..0.543 rows=0 loops=588)
Index Cond: (campaignid = b.tbl_campaign_id)
Filter: ((campaignid = COALESCE(campaignid)) AND (date(insert_datetime) >= '2020-05-23'::date) AND (date(insert_datetime) <= '2020-06-23'::date))
Rows Removed by Filter: 656
-> Index Scan using testh21_campaignid_idx on testh21 a_1 (cost=0.42..585.94 rows=1 width=20) (actual time=0.002..0.796 rows=606 loops=588)
Index Cond: (campaignid = b.tbl_campaign_id)
Filter: ((campaignid = COALESCE(campaignid)) AND (date(insert_datetime) >= '2020-05-23'::date) AND (date(insert_datetime) <= '2020-06-23'::date))
-> Index Scan using idx_user_id_tbl_user_c_1592227657_19 on tbl_user_channel f (cost=0.14..0.24 rows=1 width=422) (actual time=0.002..0.004 rows=9 loops=356244)
Index Cond: (user_id = b.user_id)
-> Index Scan using "idx_FK_6958qvy_tbl_user_c_1592228774_151" on tbl_user_configurations g (cost=0.14..0.20 rows=1 width=8) (actual time=0.002..0.002 rows=1 loops=3206196)
Index Cond: (user_id = e.user_id)
Filter: (msg_cat_id = COALESCE(msg_cat_id))
Planning Time: 6.561 ms
Execution Time: 27477.860 ms

Answer 1

There is a gross underestimate of the result rows for the index scan on testh21. The consequence is that PostgreSQL chooses nested loop joins, which is where your time is spent.
Try the following:
New statistics:
ANALYZE testh21;
If that improves the estimate, make sure that autoanalyze treats the table more often.
Prevent bad estimates caused by correlation:
CREATE STATISTICS testh21_stat (dependencies)
ON campaignid, insert_datetime FROM testh21;
ANALYZE testh21;
Perhaps there is a correlation between the columns, and that improves the estimate.
More detailed statistics: try raising default_statistics_target before ANALYZE of the table.
If you cannot improve the estimates, take the hammer and set enable_nestloop = off for the duration of the query.