Delta Encoding

Delta encoding is an annotation that instructs the encoder to write differences between consecutive values instead of absolute values. This is useful for time-series data where consecutive readings are close together.

message TimeSeries {
    timestamps @0 : array<u64 @delta>
    values     @1 : array<i32 @delta @zigzag>
}

How it works

With @delta, the encoder writes:

1. The first value as-is
2. Each subsequent value as current - previous

The decoder reverses the process, accumulating deltas to reconstruct absolute values.

When to use delta encoding

Delta encoding is most effective when:

• Values increase monotonically (timestamps, sequence numbers)
• Consecutive values are close together (sensor readings, coordinates)
• Combined with @varint or @zigzag -- small deltas compress to fewer bytes

Combining annotations

Delta encoding composes with other encoding annotations:

message GpsTrack {
    timestamps @0 : array<u64 @delta @varint>    # monotonic, small deltas
    latitudes  @1 : array<i32 @delta @zigzag>    # signed deltas near zero
    longitudes @2 : array<i32 @delta @zigzag>
}

Note: Delta encoding support is currently specified but implementation may vary by backend. Check the limitations document for current status.

See the language specification for the full normative reference.