We have deployed multi-center but got performance issue. When the nodes on other center are up, the read response time from clients is 4 or 5 times higher. when we take those nodes down, the response time becomes normal(compare to the time before we changed to multi-center).

We have high volume on the cluster, the consistency level is one for read. so my understanding is most of traffic between data center should be read repair. but seems that could not create much delay.

What could cause the problem? how to debug this?

Here is the keyspace,

[default@dsat] describe dsat;
Keyspace: dsat:
  Replication Strategy: org.apache.cassandra.locator.NetworkTopologyStrategy
  Durable Writes: true
    Options: [dc2:1, dc1:3]
  Column Families:
    ColumnFamily: categorization_cache


Datacenter: dc1
|/ State=Normal/Leaving/Joining/Moving
--  Address           Load       Tokens  Owns (effective)  Host ID                               Rack
UN  xx.xx.xx..111       59.2 GB    256     37.5%             4d6ed8d6-870d-4963-8844-08268607757e  rac1
DN  xx.xx.xx..121       99.63 GB   256     37.5%             9d0d56ce-baf6-4440-a233-ad6f1d564602  rac1
UN  xx.xx.xx..120       66.32 GB   256     37.5%             0fd912fb-3187-462b-8c8a-7d223751b649  rac1
UN  xx.xx.xx..118       63.61 GB   256     37.5%             3c6e6862-ab14-4a8c-9593-49631645349d  rac1
UN  xx.xx.xx..117       68.16 GB   256     37.5%             ee6cdf23-d5e4-4998-a2db-f6c0ce41035a  rac1
UN  xx.xx.xx..116       32.41 GB   256     37.5%             f783eeef-1c51-4f91-ab7c-a60669816770  rac1
UN  xx.xx.xx..115       64.24 GB   256     37.5%             e75105fb-b330-4f40-aa4f-8e6e11838e37  rac1
UN  xx.xx.xx..112       61.32 GB   256     37.5%             2547ee54-88dd-4994-a1ad-d9ba367ed11f  rac1
Datacenter: dc2
|/ State=Normal/Leaving/Joining/Moving
--  Address           Load       Tokens  Owns (effective)  Host ID                               Rack
DN  xx.xx.xx.199    58.39 GB   256     50.0%             6954754a-e9df-4b3c-aca7-146b938515d8  rac1
DN  xx.xx.xx..61      33.79 GB   256     50.0%             91b8d510-966a-4f2d-a666-d7edbe986a1c  rac1

Thank you in advance,