AI / LlamaIndex Interview Questions
What is the role of the CallbackManager in LlamaIndex?
The CallbackManager is LlamaIndex's hook system for observing what happens inside a pipeline, firing events at points like an LLM call starting or finishing, an embedding call, or a retrieval step, without you having to modify the core pipeline code.
It's the mechanism behind common debugging needs: token counting handlers can tally usage across a whole run, tracing handlers can record latency per step to find bottlenecks, and integrations with observability tools such as Arize Phoenix or W&B plug in through the same callback interface to visualize an entire query's execution trace.
You attach handlers to it via Settings.callback_manager or by passing one directly into a component, and because it's event-based, adding a new handler for logging or monitoring doesn't require touching the retrieval or synthesis logic itself.
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