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NOTE: The instrumentation module (available in llama-index v0.10.20 and later) is meant to replace the legacy callbacks module. During the deprecation period, the llama-index library supports both modules as a means to instrument your LLM application. However, at some point after all of the existing integrations have moved over to the new instrumentation module, we will no longer support callbacks module.

The new instrumentation module allows for the instrumentation of llama-index applications. In particular, one can handle events and track spans using both custom logic as well as those offered in the module. Users can also define their own events and specify where and when in the code logic that they should be emitted. Listed below are the core classes as well as their brief description of the instrumentation module:

  • Event — represents a single moment in time that a certain occurrence took place within the execution of the application’s code.
  • EventHandler — listen to the occurrences of Event's and execute code logic at these moments in time.
  • Span — represents the execution flow of a particular part in the application’s code and thus contains Event's.
  • SpanHandler — is responsible for the entering, exiting, and dropping (i.e., early exiting due to error) of Span's.
  • Dispatcher — emits Event's as well as signals to enter/exit/drop a Span to the appropriate handlers.


Using the new instrumentation module involves 3 high-level steps.

  1. Define a dispatcher
  2. Define and attach your EventHandler's to dispatcher
  3. Define and attach your SpanHandler to dispatcher

Doing so, would result in the ability to handle events and obtain spans that have been transmitted throughout the llama-index library and extension packages.

Defining a custom EventHandler#

Users can create their own custom handlers by subclassing BaseEventHandler and providing logic to the abstract method handle().

from llama_index.core.instrumentation.event_handlers.base import (

class MyEventHandler(BaseEventHandler):
    """My custom EventHandler."""

    def class_name(cls) -> str:
        """Class name."""
        return "MyEventHandler"

    def handle(self, event: BaseEvent, **kwargs) -> Any:
        """Logic for handling event."""

my_event_handler = MyEventHandler()

After defining your handler, you can attach it to the desired dispatcher:

import llama_index.core.instrumentation as instrument

dispatcher = instrument.get_dispatcher(__name__)

Defining a custom Event#

User can create their own custom events by subclassing BaseEvent. The BaseEvent class comes with a timestamp as well as an id_ field. To add more items to this event payload, simply add them in as new Fields (since they are subclasses of pydantic.BaseModel).

from llama_index.core.instrumentation.event.base import BaseEvent

class MyEvent(BaseEvent):
    """My custom Event."""

    new_field_1 = Field(...)
    new_field_2 = Field(...)

Once you have your custom event defined, you use a dispatcher to fire the event at desired instances throughout your application’s code.

import llama_index.core.instrumentation as instrument

dispatcher = instrument.get_dispatcher(__name__)
dispatcher.event(MyEvent(new_field_1=..., new_field_2=...))

Defining a custom Span#

Span’s are like Event's in that they are both structured data classes. Unlike Event's though, Span's as their name implies, span a duration of time within the programs execution flow. You can define a custom Span to store any information you would like.

from typing import Any
from llama_index.core.bridge.pydantic import Field

class MyCustomSpan(BaseSpan):
    custom_field_1: Any = Field(...)
    custom_field_2: Any = Field(...)

To handle your new Span type, you need to also define your custom SpanHandler by subclassing the BaseSpanHandler class. Three abstract methods need to be defined when subclass this base class, namely: new_span(), prepare_to_exit_span(), and prepare_to_drop_span().

from typing import Any, Optional
from llama_index.core.instrumentation.span.base import BaseSpan
from llama_index.core.instrumentation.span_handlers import BaseSpanHandler

class MyCustomSpanHandler(BaseSpanHandler[MyCustomSpan]):
    def class_name(cls) -> str:
        """Class name."""
        return "MyCustomSpanHandler"

    def new_span(
        self, id: str, parent_span_id: Optional[str], **kwargs
    ) -> Optional[MyCustomSpan]:
        """Create a span."""
        # logic for creating a new MyCustomSpan

    def prepare_to_exit_span(
        self, id: str, result: Optional[Any] = None, **kwargs
    ) -> Any:
        """Logic for preparing to exit a span."""

    def prepare_to_drop_span(
        self, id: str, err: Optional[Exception], **kwargs
    ) -> Any:
        """Logic for preparing to drop a span."""

To make use of your new SpanHandler (and associated Span type), you simply need to add it to your desired dispatcher.

import llama_index.core.instrumentation as instrument
from llama_index.core.instrumentation.span_handler import SimpleSpanHandler

dispatcher = (
)  # with no name argument, defaults to root

my_span_handler = MyCustomSpanHandler()

Entering/Exiting a Span#

To send a signal to SpanHandler's to enter/exit a Span, we use the span_enter(), span_exit() methods, respectively. There is also span_drop() method that could be used to handle cases where Span's are cut shorter than usual due to errors within the covered code’s execution.

import llama_index.core.instrumentation as instrument

dispatcher = instrument.get_dispatcher(__name__)

def func():
        val = ...
        return val

# or, syntactic sugar via decorators

def func():

Making use of dispatcher hierarchy#

A similar hierarchy to that seen with the standard Python logging library and its Logger class exists for dispatcher. Specifically, all dispatcher’s except for the root dispatcher has a parent, and when handling events or span’s can propagate them to its parent as well (this is the default behaviour). This hierarchical method of handling events and spans allows for defining “global” event handlers as well as “local” ones.

Consider the project structure defined below. There are 3 dispatcher's: one at the top-level of the project and then two others at the individual sub-modules llama1 and llama2. With this setup, any EventHandler’s attached to the project root’s dispatcher will be be subscribed to all Event's that occur in the execution of code in llama1 and llama2. On the other hand, EventHandler's defined in the respective llama<x> sub modules will only be subscribed to the Event's that occur within their respective sub-module execution.

├──  # has a dispatcher=instrument.get_dispatcher(__name__)
├── llama1
│   ├──  # has a dispatcher=instrument.get_dispatcher(__name__)   └──
└── llama2
    ├──  # has a dispatcher=instrument.get_dispatcher(__name__)

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