The perfmetrics package provides a simple way to add software performance metrics to Python libraries and applications. Use perfmetrics to find the true bottlenecks in a production application.
The perfmetrics package is a client of the Statsd daemon by Etsy, which is in turn a client of Graphite (specifically, the Carbon daemon). Because the perfmetrics package sends UDP packets to Statsd, perfmetrics adds no I/O delays to applications and little CPU overhead. It can work equally well in threaded (synchronous) or event-driven (asynchronous) software.
@metricmethod decorators to wrap functions
and methods that should send timing and call statistics to Statsd.
Add the decorators to any function or method that could be a bottleneck,
including library functions.
from perfmetrics import metric from perfmetrics import metricmethod @metric def myfunction(): """Do something that might be expensive""" class MyClass(object): @metricmethod def mymethod(self): """Do some other possibly expensive thing"""
Next, tell perfmetrics how to connect to Statsd. (Until you do, the decorators have no effect.) Ideally, either your application should read the Statsd URI from a configuration file at startup time, or you should set the STATSD_URI environment variable. The example below uses a hard-coded URI:
from perfmetrics import set_statsd_client set_statsd_client('statsd://localhost:8125') for i in xrange(1000): myfunction() MyClass().mymethod()
If you run that code, it will fire 2000 UDP packets at port 8125. However, unless you have already installed Graphite and Statsd, all of those packets will be ignored and dropped. Dropping is a good thing: you don't want your production application to fail or slow down just because your performance monitoring system is stopped or not working.
Install Graphite and Statsd to receive and graph the metrics. One good way to install them is the graphite_buildout example at github, which installs Graphite and Statsd in a custom location without root access.
Pyramid and WSGI
If you have a Pyramid app, you can set the
statsd_uri for each
request by including perfmetrics in your configuration:
config = Configuration(...) config.include('perfmetrics')
Also add a
statsd_uri setting such as
Once configured, the perfmetrics tween will set up a Statsd client for
the duration of each request. This is especially useful if you run
multiple apps in one Python interpreter and you want a different
statsd_uri for each app.
Similar functionality exists for WSGI apps. Add the app to your Paste Deploy pipeline:
[statsd] use = egg:perfmetrics#statsd statsd_uri = statsd://localhost:8125 [pipeline:main] pipeline = statsd egg:myapp#myentrypoint
While most programs send metrics from any thread to a single global
Statsd server, some programs need to use a different Statsd server
for each thread. If you only need a global Statsd server, use the
set_statsd_client function at application startup. If you need
to use a different Statsd server for each thread, use the
statsd_client_stack object in each thread. Use the
Graphite stores each metric as a time series with multiple resolutions. The sample graphite_buildout stores 10 second resolution for 48 hours, 1 hour resolution for 31 days, and 1 day resolution for 5 years. To produce a coarse grained value from a fine grained value, Graphite computes the mean value (average) for each time span.
Because Graphite computes mean values implicitly, the most sensible way to treat counters in Graphite is as a "hits per second" value. That way, a graph can produce correct results no matter which resolution level it uses.
Treating counters as hits per second has unfortunate consequences, however. If some metric sees a 1000 hit spike in one second, then falls to zero for at least 9 seconds, the Graphite chart for that metric will show a spike of 100, not 1000, since Graphite receives metrics every 10 seconds and the spike looks to Graphite like 100 hits per second over a 10 second period.
If you want your graph to show 1000 hits rather than 100 hits per second,
apply the Graphite
hitcount() function, using a resolution of
10 seconds or more. The hitcount function converts per-second
values to approximate raw hit counts. Be sure
to provide a resolution value large enough to be represented by at least
one pixel width on the resulting graph, otherwise Graphite will compute
averages of hit counts and produce a confusing graph.
It usually makes sense to treat null values in Graphite as zero, though that is not the default; by default, Graphite draws nothing for null values. You can turn on that option for each graph.
- Notifies Statsd using UDP every time the function is called.
Sends both call counts and timing information. The name of the metric
sent to Statsd is
@metric, but the name of the Statsd metric is
<class module>.<class name>.<method name>.
- Metric(stat=None, rate=1, method=False, count=True, timing=True)
A decorator or context manager with options.
statis the name of the metric to send; set it to None to use the name of the function or method.
ratelets you reduce the number of packets sent to Statsd by selecting a random sample; for example, set it to 0.1 to send one tenth of the packets. If the
methodparameter is true, the default metric name is based on the method's class name rather than the module name. Setting
countto False disables the counter statistics sent to Statsd. Setting
timingto False disables the timing statistics sent to Statsd.
Sample use as a decorator:
@Metric('frequent_func', rate=0.1, timing=False) def frequent_func(): """Do something fast and frequently"""
Sample use as a context manager:
def do_something(): with Metric('doing_something'): pass
If perfmetrics sends packets too frequently, UDP packets may be lost and the application performance may be affected. You can reduce the number of packets and the CPU overhead using the
Metricdecorator with options instead of
metricmethod. The decorator example above uses a sample rate and a static metric name. It also disables the collection of timing information.
When using Metric as a context manager, you must provide the
statparameter or nothing will be recorded.
- Return the currently configured
StatsdClient. Returns the thread-local client if there is one, or the global client if there is one, or None.
- Set the global
client_or_urican be a StatsdClient, a
statsd://URI, or None. Note that when the perfmetrics module is imported, it looks for the
STATSD_URIenvironment variable and calls set_statsd_client() if that variable is found.
- Create a
StatsdClientfrom a URI, but do not install it as the global StatsdClient. A typical URI is
statsd://localhost:8125. Supported optional query parameters are
gauge_suffix. The default prefix is empty and the default gauge_suffix is
.<host_name>. See the
StatsdClientdocumentation for more information about
Python code can send custom metrics by first getting the current
StatsdClient using the
statsd_client() function. Note that
statsd_client() returns None if no client has been configured.
Most of the methods below have optional
buf parameters. The
rate parameter, when set to a value
less than 1, causes StatsdClient to send a random sample of packets rather
than every packet. The
rate_applied parameter, if true, informs
StatsdClient that the sample rate has already been applied and the
packet should be sent regardless of the specified sample rate.
buf parameter is a list, StatsdClient
appends the packet contents to the
buf list rather than send the
packet, making it possible to send multiple updates in a single packet.
Keep in mind that the size of UDP packets is limited (the limit varies
by the network, but 1000 bytes is usually a good guess) and any extra
bytes will be ignored silently.
- timing(stat, value, rate=1, buf=None, rate_applied=False)
- Record timing information.
statis the name of the metric to record and
valueis the timing measurement in milliseconds. Note that Statsd maintains several data points for each timing metric, so timing metrics can take more disk space than counters or gauges.
- gauge(stat, value, suffix=None, rate=1, buf=None, rate_applied=False)
- Update a gauge value.
statis the name of the metric to record and
valueis the new gauge value. A gauge represents a persistent value such as a pool size. Because gauges from different machines often conflict, a suffix is usually applied to gauge names. If the
suffixparameter is a string (including an empty string), it overrides the default gauge suffix.
- incr(stat, count=1, rate=1, buf=None, rate_applied=False)
- Increment a counter by
count. Note that Statsd clears all counter values every time it sends the metrics to Graphite, which usually happens every 10 seconds. If you need a persistent value, it may be more appropriate to use a gauge instead of a counter.
- decr(stat, count=1, rate=1, buf=None, rate_applied=False)
- Decrement a counter by
- Send the contents of the
buflist to Statsd.