Remove Copy Bound from NodeId

[drmingdrmer]

Remove Copy Bound from NodeId

Current Situation

The NodeId type is currently defined in src/node.rs as:

type NodeId: .. + Copy + .. + 'static;

This definition restricts applications from using non-Copy types such as String as NodeId.

Proposed Change

We propose removing the Copy bound from NodeId. This modification will allow the use of non-Copy types as NodeId, providing greater flexibility for applications that prefer variable-length strings or other non-Copy types for node identification.

These change should maintain compatibility and must not break applications.

Implementation Details

To implement this change, we need to:

1. Replace all copy operations with explicit .clone() calls.
2. Update derived Copy implementations with manual implementations where necessary, in order to maintain compatibility. For example:

   // Before
   #[derive(Copy...)]
   pub struct LogId<NID: NodeId> {}
   
   // After
   impl<NID: Copy> Copy for LogId<NID> {}

Performance Considerations

Our analysis suggests that the performance impact of this change will be negligible for simple objects that don't involve heap allocation. Benchmarks comparing Clone and Copy for non-heap-allocated objects show nearly identical performance:

Benchmark Results

This means:

• Existing applications using Copy types for NodeId should see no significant performance changes.
• New applications using non-Copy types for NodeId may experience a slight performance difference, but it should be minimal in most cases.

Benefits

This change will:

1. Increase flexibility for NodeId type selection in applications.
2. Allow the use of more complex or variable-length identifiers when needed.
3. Maintain performance for existing use cases while opening up new possibilities.

We believe this modification will enhance Openraft's versatility without compromising its current functionality or performance.

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[SteveLauC]

I second this!

Actually, I was indeed surprised that the NodeId needs to be Copy when accessing Openraft for the first time.

New applications using non-Copy types for NodeId may experience a slight performance difference, but it should be minimal in most cases.

Perhaps we could document the impact of the .clone() within Openraft, something like:

Be aware that NodeId will be .clone()d within Openraft so that heap-allocated NodeId could lead to slightly bad performance.