Coordinator node timed out on Cassandra cqlsh shell - cassandra

Question

I am new to cassandra and trying to do multi node setup on two Mac machine. Its not a datastax casandra.
like my Ip is 10.100.1.12 and other machine ip is 10.100.1.15. I have changed the following properties in cassandra.yaml files on bothe the machine:
10.100.1.15:
seeds: "127.0.0.1,10.100.1.12,10.100.1.15"
listen_address: 10.100.1.15
rpc_address: 10.100.1.15
endpoint_snitch: GossipingPropertyFileSnitch
10.100.1.12:
seeds: "127.0.0.1,10.100.1.12,10.100.1.15"
listen_address: 10.100.1.12
rpc_address: 10.100.1.12
endpoint_snitch: GossipingPropertyFileSnitch
cassandra runs fine cqlsh is also opening using the command
bin/cqlsh 10.100.1.12
but when i am trying to retrieve the count of tables its showing me the error:
ReadTimeout: Error from server: code=1200 [Coordinator node timed out waiting for replica nodes' responses] message="Operation timed out - received only 0 responses." info={'received_responses': 0, 'required_responses': 1, 'consistency': 'ONE'}
i tried changing the read_request_timeout_in_ms proprtty from 5000 to 20000 but still i am getting the same error. Could anyone please help what i am doing wrong?
the table schema is following:
cqlsh:app_auditor> describe table traffic_data;
CREATE TABLE app_auditor.traffic_data (
current_time bigint PRIMARY KEY,
appid bigint,
attributes map<text, text>,
device bigint,
flow_type text,
message_time bigint
) WITH bloom_filter_fp_chance = 0.01
AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
AND comment = ''
AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
AND crc_check_chance = 1.0
AND dclocal_read_repair_chance = 0.1
AND default_time_to_live = 0
AND gc_grace_seconds = 86400
AND max_index_interval = 2048
AND memtable_flush_period_in_ms = 0
AND min_index_interval = 128
AND read_repair_chance = 0.0
AND speculative_retry = '99PERCENTILE';
the count query i am using is
select count(*) from traffic_data;

Answer 1

In Cassandra count(*) is very costly, cassandra needs to scan all the row from all the node just to give you the count, that's why it's giving you timeout exception.
Instead of using count(*) maintain a counter table, like the below one :
CREATE TABLE traffic_counter (
type int PRIMARY KEY,
traffic_count counter
);
When a data insert into traffic_data data, increment the value of traffic_count
UPDATE traffic_counter SET traffic_count = traffic_count + 1 WHERE type = 0;
Now you can select traffic count very efficiently.
SELECT traffic_count FROM traffic_counter WHERE type = 0;