Config advice for scylla driver

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Cong Guo

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Nov 17, 2021, 3:45:30 AM11/17/21
to ScyllaDB users
Background is below
1. 3x i3.4xlarge EC2
2. 3 replicas
3. Client use Scylla CQL Driver

Question is:
1. If we configure the connection number to 1 on the client side, will all the request route to one fixed ec2 which cause the coordinator inbalance?
2. Is there any tuning method to reduce the impact of write traffic on read?

the client default conf is: Protocol version is V4 Pooling options - coreConnectionsPerHostLocal: 1 maxConnectionsPerHostLocal: 1 coreConnectionsPerHostRemote: 1 maxConnectionsPerHostRemote: 1 maxReqPerConnHostLocal: 1024 maxReqPerConnHostRemote: 256

Avi Kivity

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Nov 17, 2021, 3:55:51 AM11/17/21
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On 11/17/21 10:45, 'Cong Guo' via ScyllaDB users wrote:
Background is below
1. 3x i3.4xlarge EC2
2. 3 replicas
3. Client use Scylla CQL Driver

Question is:
1. If we configure the connection number to 1 on the client side, will all the request route to one fixed ec2 which cause the coordinator inbalance?


No. Drivers will open one connection per node, not one connection in total. In addition the Scylla shard-aware driver will open one connection per shard. You can verify this using the monitoring, it shows how many connections are active, or using the `ss` tool.


2. Is there any tuning method to reduce the impact of write traffic on read?


In Scylla Enterprise you can define different resource shares for different sessions, and then direct reads and writes into different sessions [1]. In Scylla open source you can adjust the client-side concurrency.


[1] https://docs.scylladb.com/using-scylla/workload-prioritization/



the client default conf is: Protocol version is V4 Pooling options - coreConnectionsPerHostLocal: 1 maxConnectionsPerHostLocal: 1 coreConnectionsPerHostRemote: 1 maxConnectionsPerHostRemote: 1 maxReqPerConnHostLocal: 1024 maxReqPerConnHostRemote: 256
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Cong Guo

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Nov 17, 2021, 3:56:55 AM11/17/21
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Many thanks.
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