This class represents the options of the rust driver Default Load Balancing Policy. This option will be used to configure that policy. You can find more about this policy in the documentation: https://rust-driver.docs.scylladb.com/stable/load-balancing/default-policy.html
The hosts address in the format ipAddress:port. When the list is provided, only hosts from this list may get connected to (whether they will get connected to or not depends on the other policy options).
Sets whether this policy should shuffle replicas when token-awareness is enabled. Shuffling can help distribute the load over replicas, but can reduce the effectiveness of caching on the database side (e.g. for reads).
This option is enabled by default. If disabled, replicas will be chosen in some random order that is chosen when the load balancing policy is created and will not change over its lifetime.
Sets whether this policy permits datacenter failover, i.e. ever attempts to send requests to nodes from a non-preferred datacenter.
In the event of a datacenter outage or network failure, the nodes
in that datacenter may become unavailable, and clients may no longer
be able to access data stored on those nodes. To address this,
the DefaultPolicy supports datacenter failover, which allows routing
requests to nodes in other datacenters if the local nodes are unavailable.
Datacenter failover can be enabled in DefaultPolicy setting this flag.
When it is set, the policy will prefer to return alive remote replicas
if datacenter failover is permitted.
Sets the datacenter to be preferred by this policy.
Allows the load balancing policy to prioritize nodes based on their location. When a preferred datacenter is set, the policy will treat nodes in that datacenter as "local" nodes, and nodes in other datacenters as "remote" nodes. This affects the order in which nodes are returned by the policy when selecting replicas for read or write operations. If no preferred datacenter is specified, the policy will treat all nodes as local nodes.
When datacenter failover is disabled (permitDcFailover is set to false),
the default policy will only include local nodes in load balancing plans.
Remote nodes will be excluded, even if they are alive and available
to serve requests.
This option cannot be used without setting preferDatacenter.
preferDatacenter and preferRack set the datacenter and rack to be preferred by this policy.
Allows the load balancing policy to prioritize nodes based on their location as well as their availability zones in the preferred datacenter.
When a preferred rack is set, the policy will first return replicas in the local rack in the preferred datacenter, and then the other replicas in the datacenter.
Sets whether this policy is token-aware (balances load more consciously) or not.
Token awareness refers to a mechanism by which the driver is aware of the token range assigned to each node in the cluster. Tokens are assigned to nodes to partition the data and distribute it across the cluster.
When a user wants to read or write data, the driver can use token awareness to route the request to the correct node based on the token range of the data being accessed. This can help to minimize network traffic and improve performance by ensuring that the data is accessed locally as much as possible.
In the case of DefaultPolicy, token awareness is enabled by default,
meaning that the policy will prefer to return alive local replicas
if the token is available. This means that if the client is requesting data
that falls within the token range of a particular node, the policy will try
to route the request to that node first, assuming it is alive and responsive.
Token awareness can significantly improve the performance and scalability of applications built on Scylla. By using token awareness, users can ensure that data is accessed locally as much as possible, reducing network overhead and improving throughput.