Projection Operator
The Projection Operator implements the Project relation defined in substrait. The Projection operator is stateless and does not need to store any state.
As defined in substrait, it takes in two properties, input which is the operator that feeds the projection, and an array of expressions which defines how data should be projected. It also implements the common Emit field which allows a user to reduce the amount of data outputted by the operator. All expressions defined in the array will have an emit index offset by the input length.
Metrics
The Projection Operator has the following metrics:
| Metric Name | Type | Description |
|---|---|---|
| busy | Gauge | Value 0-1 on how busy the operator is. |
| backpressure | Gauge | Value 0-1 on how much backpressure the operator has. |
| health | Gauge | Value 0 or 1, if the operator is healthy or not. |
| events | Counter | How many events that pass through the operator. |
info
At this point, a projection operator will never be unhealthy.