LightStep collects spans from different parts of an instrumented application and assembles traces by joining these spans together. LightStep does not assemble every trace: instead it only assembles traces that serve as examples of application errors, high latency, or other interesting events.
When spans are first received by a LightStep collector, they are placed in a temporary buffer. Collector recall measures the amount of time covered by spans in this buffer. It indicates how far back into the past LightStep can look to find spans while assembling a trace. For example, if the current recall is 5 minutes, then when an application error occurs, any spans that were reported in the last 5 minutes can be assembled as part of a trace for that error.
If you see an error that indicates your project has “insufficient recall,” this means that your collector pool is under-provisioned. If you are using the shared collector pool offered by LightStep, either decrease the rate of spans sent to the pool or contact email@example.com. If you are using an on-prem collector pool, consider increasing the size of the pool or choosing machines with more memory.
Collector Recall != Trace Retention
Note that collector recall is only relevant to spans that have not yet been assembled as part of a trace. Once a trace has been assembled, all spans in that trace will be retained indefinitely.