django-cavalry

A Performance Tracer!

Setup

• Add 'cavalry.middleware.cavalry' to your middleware.
• Add CAVALRY_ENABLED = bool(DEBUG) (or similar~) to your settings.

Settings – General

CAVALRY_ENABLED

(boolean, default False)

Master switch for the middleware.

This is toggleable during runtime. That is, it does not wholesale disable the middleware forever via the MiddlewareNotUsed mechanism.

CAVALRY_PROBABILITY

(float, default 1)

Probability (0..1) for a request to be traced; useful in production.

CAVALRY_DB_RECORD_STACKS

(boolean, default True)

Whether or not database stack traces should be recorded. Recording stack traces naturally has a performance impact.

Settings – Posting

The requests library must be available for posting to work.

You can install it by hand, or by using the [poster] extra while installing Cavalry.

CAVALRY_ELASTICSEARCH_URL_TEMPLATE

(string)

An URL template for posting payloads to Elasticsearch. {curly-braced} segments are interpolated using Python syntax. All fields in the payload are available, plus {ymd} is the YYYY-MM-DD of the current time. If falsy, no Elasticsearch posting is attempted.

An useful default might be 'http://localhost:9200/my-app-{ymd}/item'. This is easily ingestible by Kibana.

CAVALRY_THREADED_POST

(boolean, default False)

Whether or not to execute posting in another thread.

Enabling this has a positive performance impact in that formatting and submitting data to Elasticsearch data will not tie up request handling.

On the flipside, though, if the worker process dies before posting is complete, the trace is lost.

Also, if you're running on uWSGI, make sure enable-threads is set.

CAVALRY_POST_STACKS

(boolean, default True)

Whether or not post stack traces.

Not posting stack traces makes the ES payloads smaller.

Runtime

When

• running in DEBUG, or
• when you're a superuser, or
• if request._cavalry_can_inject_stats is truthy (e.g. via a middleware of your own design)
  • Note that this may, especially in conjunction with _cavalry_stacks, reveal sensitive information. Be very diligent with that middleware.

Cavalry injects a small perf bar into each rendered HTML page, as well as a script segment that outputs SQL queries into the dev console.

By default, stack traces are not printed for the SQL queries; add the _cavalry_stacks query parameter to have them printed too.