pip/pip-358.md

# PIP-358: let resource weight work for OverloadShedder, LeastLongTermMessageRate, ModularLoadManagerImpl.

# Background knowledge

Initially, we introduce `loadBalancerCPUResourceWeight`, `loadBalancerBandwidthInResourceWeight`, `loadBalancerBandwidthOutResourceWeight`,
`loadBalancerMemoryResourceWeight`, `loadBalancerDirectMemoryResourceWeight` in `ThresholdShedder` to control the resource weight for
different resources when calculating the load of the broker.
Then we let it work for `LeastResourceUsageWithWeight` for better bundle placement policy.

But https://github.com/apache/pulsar/pull/19559 and https://github.com/apache/pulsar/pull/21168 have pointed out that the actual load
of the broker is not related to the memory usage and direct memory usage, thus we have changed the default value of
`loadBalancerMemoryResourceWeight`, `loadBalancerDirectMemoryResourceWeight` to 0.0.

There are still some places where memory usage and direct memory usage are used to calculate the load of the broker, such as
`OverloadShedder`, `LeastLongTermMessageRate`, `ModularLoadManagerImpl`. We should let the resource weight work for these places
so that we can set the resource weight to 0.0 to avoid the impact of memory usage and direct memory usage on the load of the broker.

# Motivation

The actual load of the broker is not related to the memory usage and direct memory usage, thus we should let the resource weight work for
`OverloadShedder`, `LeastLongTermMessageRate`, `ModularLoadManagerImpl` so that we can set the resource weight to 0.0 to avoid the impact of
memory usage and direct memory usage on the load of the broker.


# Detailed Design

Let resource weight work for `OverloadShedder`, `LeastLongTermMessageRate`, `ModularLoadManagerImpl`.
- For `OverloadShedder`, `LeastLongTermMessageRate`, we replace `getMaxResourceUsage()` with `getMaxResourceUsageWithWeight()` in the calculation of the load of the broker.
- For `ModularLoadManagerImpl`, we replace `getMaxResourceUsage()` with `getMaxResourceUsageWithWeight()` when checking if the broker is overloaded and decide whether to update the broker data to metadata store.

# Backward & Forward Compatibility


# Links

* Mailing List discussion thread: https://lists.apache.org/thread/lj34s3vmjbzlwmy8d66d0bsb25vnq9ky
* Mailing List voting thread: https://lists.apache.org/thread/b7dzm0yz6l40pkxmxhto5mro7brmz57r