[processor/tailsampling] Added bytes_limiting policy type

[portertech]

This pull-request introduces a new tailsampling processor sampling policy type, bytes_limiting.

Bytes Limiting Policy

The bytes_limiting policy uses a token bucket algorithm implemented by golang.org/x/time/rate to control the rate of data throughput.

This policy is particularly useful for:

• Volume control: Limiting the total amount of trace data processed per unit time
• Burst handling: Allowing short-term spikes in data volume while maintaining long-term rate limits
• Memory protection: Preventing downstream systems from being overwhelmed by large traces

Configuration

The bytes_limiting policy supports the following configuration parameters:

• bytes_per_second: The sustained rate at which bytes are allowed through (required)
• burst_capacity: The maximum number of bytes that can be processed in a burst (optional, defaults to 2x bytes_per_second)

Token Bucket Algorithm

The policy implements a token bucket algorithm where:

1. Tokens represent bytes: Each token in the bucket represents one byte of trace data
2. Continuous refill: Tokens are added to the bucket at the configured bytes_per_second rate
3. Burst capacity: The bucket can hold up to burst_capacity tokens for handling traffic bursts
4. Consumption: When a trace arrives, tokens equal to the trace size are consumed from the bucket
5. Rejection: If insufficient tokens are available, the trace is not sampled

Example Configuration

processors:                                                                                                                                                                                          
  tail_sampling:                                                                                                                                                                                     
    policies:                                                                                                                                                                                        
      - name: volume-control                                                                                                                                                                         
        type: bytes_limiting                                                                                                                                                                         
        bytes_limiting:                                                                                                                                                                              
          bytes_per_second: 1048576    # 1 MB/second sustained rate
          burst_capacity: 5242880      # 5 MB burst capacity                                                                                                                                         

[Logiraptor]

The actual change looks good to me, nice and simple. Looks like there's some extra stuff in here though

[atoulme]

this makes the assumption that the traces will be serialized to proto format, is there a way to allow a different encoding, for example using the encoding extension?

[portertech]

curious, when would this processor encounter other encodings?

[atoulme]

OTLP JSON is one. Splunk HEC another. You can see all the encodings we support under extensions/encoding.

[atoulme]

Opening #44416 to follow up.

[atoulme]

I think this can get in, just need to have an issue open to follow up on the marshaling strategy to count bytes.