Logging Breadcrumbs

Newer Sentry versions support logging of breadcrumbs in addition of errors. This means that whenever an error or other Sentry event is submitted to the system, breadcrumbs that were logged before are sent along to make it easier to reproduce what lead up to an error.

In the default configuration the Python client instruments the logging framework and a few popular libraries to emit crumbs.

You can however also manually emit events if you want to do so. There are a few ways this can be done.

Breadcrumbs are enabled by default but starting with Raven 5.15 you can disable them on a per-client basis by passing enable_breadcrumbs=False to the client constructor.

Enabling / Disabling Instrumentation

When a sentry client is constructed then the raven library will by default automatically instrument some popular libraries. There are a few ways this can be controlled by passing parameters to the client constructor:

install_logging_hook:
If this keyword argument is set to False the Python logging system will not be instrumented. Note that this is a global instrumentation so that if you are using multiple sentry clients at once you need to disable this on all of them.
hook_libraries:

This is a list of libraries that you want to hook. The default is to hook all libraries that we have integrations for. If this is set to an empty list then no libraries are hooked.

The following libraries are supported currently:

  • 'requests': hooks the Python requests library.
  • 'httplib': hooks the stdlib http library (also hooks urllib in the process)

Additionally framework integration will hook more things automatically. For instance when you use Django, database queries will be recorded.

Another option to control what happens is to register special handlers for the logging system or to disable loggers entirely. For this you can use the ignore_logger() and register_special_log_handler() functions:

raven.breadcrumbs.ignore_logger(name_or_logger)

If called with the name of a logger, this will ignore all messages that come from that logger. For instance if you have a very spammy logger you can disable it this way.

raven.breadcrumbs.register_special_log_handler(name_or_logger, callback)

This registers a callback as a handler for a given logger. This can be used to ignore or convert log messages. The callback is invoked with the following arguments: logger, level, msg, args, kwargs. If the callback returns False nothing is logged, if it returns True the default handling kicks in.

Typically it makes sense to invoke record() from it.

raven.breadcrumbs.register_logging_handler(callback)

This is similar to register_special_log_handler() but it adds a global callback that is invoked for all log entries. Otherwise it works the same but multiple handlers can be registered.

Manually Emitting Breadcrumbs

If you want to manually record breadcrumbs the most convenient way to do that is to use the record() function which will automatically record the crumbs with the clients that are working with the current thread. This is more convenient than to call the captureBreadcrumb method on the client itself as you need to hold a reference to that.

raven.breadcrumbs.record(**options)

This function accepts keyword arguments matching the attributes of a breadcrumb. For more information see Interfaces. Additionally a processor callback can be passed which will be invoked to process the data if the crumb was not rejected.

The most important parameters:

message:
the message that should be recorded.
data:
a data dictionary that should be recorded with the event.
category:
The category for this error. This can be a module name, or just a string that clearly identifies the crumb (eg: http, rpc, etc.)
type:
can override the type if a special type should be sent to Sentry.

Example:

from raven import breadcrumbs

breadcrumbs.record(message='This is an important message',
                   category='my_module', level='warning')

Because crumbs go into a ring buffer, often it can be useful to defer processing of expensive operations until the crumb is actually needed. For this you can pass a processor which will be passed the data dict for modifications:

from raven.breadcrumbs import record

def process_crumb(data):
    data['data'] = compute_expensive_data()

breadcrumbs.record(message='This is an important message',
                   category='my_module', level='warning',
                   processor=process_crumb)