Optimisation on postgres query - postgresql

Question

I am looking for optimization suggestions for the below query on postgres. Not a DBA so looking for some expert advice in here.
Devices table holds device_id which are hexadecimal.
To achieve high throughput we run 6 instances of this query in parallel with pattern matching for device_id
beginning with [0-2], [3-5], [6-9], [a-c], [d-f]
When we run just one instance of the query it works fine, but with 6 instances we get error -
[6669]:FATAL: connection to client lost
explain analyze select notifications.id, notifications.status, events.alert_type,
events.id as event_id, events.payload, notifications.device_id as device_id,
device_endpoints.region, device_endpoints.device_endpoint as endpoint
from notifications
inner join events
on notifications.event_id = events.id
inner join devices
on notifications.device_id = devices.id
inner join device_endpoints
on devices.id = device_endpoints.device_id
where notifications.status = 'pending' AND notifications.region = 'ap-southeast-2'
AND devices.device_id ~ '[0-9a-f].*'
limit 10000;
Output of explain analyse
"Limit (cost=25.62..1349.23 rows=206 width=202) (actual time=0.359..0.359 rows=0 loops=1)"
" -> Nested Loop (cost=25.62..1349.23 rows=206 width=202) (actual time=0.357..0.357 rows=0 loops=1)"
" Join Filter: (notifications.device_id = devices.id)"
" -> Nested Loop (cost=25.33..1258.73 rows=206 width=206) (actual time=0.357..0.357 rows=0 loops=1)"
" -> Hash Join (cost=25.04..61.32 rows=206 width=52) (actual time=0.043..0.172 rows=193 loops=1)"
" Hash Cond: (notifications.event_id = events.id)"
" -> Index Scan using idx_notifications_status on notifications (cost=0.42..33.87 rows=206 width=16) (actual time=0.013..0.100 rows=193 loops=1)"
" Index Cond: (status = 'pending'::notification_status)"
" Filter: (region = 'ap-southeast-2'::text)"
" -> Hash (cost=16.50..16.50 rows=650 width=40) (actual time=0.022..0.022 rows=34 loops=1)"
" Buckets: 1024 Batches: 1 Memory Usage: 14kB"
" -> Seq Scan on events (cost=0.00..16.50 rows=650 width=40) (actual time=0.005..0.014 rows=34 loops=1)"
" -> Index Scan using idx_device_endpoints_device_id on device_endpoints (cost=0.29..5.80 rows=1 width=154) (actual time=0.001..0.001 rows=0 loops=193)"
" Index Cond: (device_id = notifications.device_id)"
" -> Index Scan using devices_pkey on devices (cost=0.29..0.43 rows=1 width=4) (never executed)"
" Index Cond: (id = device_endpoints.device_id)"
" Filter: (device_id ~ '[0-9a-f].*'::text)"
"Planning time: 0.693 ms"
"Execution time: 0.404 ms"