PIP-380: Support setting up specific namespaces to skipping the load-shedding

Background knowledge

Some of the Pulsar protocols, for example the KoP will use a system topic to store the metadata, eg: the topic‘s offset, when the bundle owner changes the topic’s data will need to be full recovered to the broker, and when unloaded, it needs to remove the broker local memory, if the topic's data were huge, it may cause slow loading.

Motivation

Support setting up specific namespaces to skipping the load-shedding, for the system topics namespace, or for benchmark-relevant namespaces we better be skipping the load shedding because for system topics, if the ownership transfers to another broker, it may need to recover the data by replaying the messages, it will cause message pub/sub temporary unavailable.

Goals

In Scope

Support setting up specific namespaces to skipping the load-shedding
Use RoundRobinBrokerSelector to assign the skipped namespaces bundle.

High Level Design

Add new configuration loadBalancerSheddingExcludedNamespaces to the ServiceConfiguration. While doing the load-shedding, filter out the configuration namespaces.

For shedding excluded namespaces, use RoundRobinBrokerSelector to assign the ownership, it can make the assignment more average because these will not automatically rebalance to another broker unless manually unloaded it.

Detailed Design

Design & Implementation Details

Public-facing Changes

Configuration

Add new configuration loadBalancerSheddingExcludedNamespaces to the ServiceConfiguration.

    @FieldContext(
            dynamic = true,
            category = CATEGORY_LOAD_BALANCER,
            doc = "The namespaces skip for load shedding"
    )
    private Set<String> loadBalancerSheddingExcludedNamespaces = new TreeSet<>();

Monitoring

No new metrics are added in this proposal.

Security Considerations

No new security considerations are added in this proposal.

Backward & Forward Compatibility

Revert

No changes are needed to revert to the previous version.

Upgrade

No other changes are needed to upgrade to the new version.

Alternatives

None