::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact

Hit frequencies

December 2nd, 2016
tech  [html]
When load testing server-side software there are two straight-forward options:
  1. Stress all endpoints evenly
  2. Stress one endpoint in isolation
For example, if you're testing a dynamic website with siege you could (1) give it a list of all the urls on your site and have it rotate among them, or you could (2) pick a representive url and just hit that one repeatedly. Like any synthetic test this isn't completely realistic, but in this case you're missing something pretty important: if you want to test something that uses caching, you need to approximate the distribution of a real workload.

Why? How well caching works depends on your hit rate, which depends on what the distribution of your requests looks like. Situation (1) is a caching worst-case, (2) is a caching best case, and your real situation is somewhere in the middle. For example, from my access logs over the past couple years, here's the distribution of requests I've seen:

1275358 /news.rss
562369 /
437312 /favicon.ico
406583 /index
168296 /robots.txt
162728 /p/
116353 /simple_piano_recordings/piano_chords.svg
94048 /icdiff
92680 /p/mercury-spill
63728 /wsgi/json-comments-cached/gp/i6WrmjSHXLg
[snip ~1k entries]
1179 /news/2011-11-02
1178 /wsgi/json-comments/gp/YTnbXQoRPRN
1178 /fiddle-clip-on/pictures/11-top.jpg
[snip ~10k entries]
113 /news/back_from_564.rss
113 /news/2012-07-24
113 /news/2012-07-09.html
[snip ~100k entries]
3 /nextbus/omnitrans/82/7387/
3 /nextbus/art/1135/759763/
3 /nextbus/mbta/39/6460/
[snip ~1M entries]
1 /ngx_pagespeed_beacon?ets=load:906&rload=1605...
1 /nextbus/jtafla/17/1433/next/
1 /news/all/trillion-dollar-platinum-coin

This is kind of a mess, but the main idea is that we have a few "hot" endpoints, and then a long tail of less popular entries. I can use this distribution in load testing, to get something between uniform sampling (option 1) and singleton sampling (option 2) that better represents what real load on the site would look like.

In case this is useful to other people, here's the frequency list (hits-frequency.txt.gz) and a short script to sample from it (generate_urls.py).

Comment via: google plus, facebook

Recent posts on blogs I like:

The Private Sector’s Role in Transit Innovation

The United States has long had private success and public failure – not just the sense of private affluence and public squalor, in which household income is high but the state of public services lags, but also in that the private sector is more productive…

via Pedestrian Observations June 17, 2019

Unintended pregnancy in folk songs

I’ve been listening to a lot of the Watersons and Waterson:Carthy this week. It’s reminded me how absolutely full British folk music is of songs about unintended pregnancy. Most commonly the result is unhappy motherhood: “But if I had kent that I now ken …

via The whole sky June 1, 2019

Programmer migration patterns

I made a little flow chart of mainstream programming languages and how programmers seem to move from one to another. There's a more common kind of chart, which shows how the languages themselves evolved. I didn't want to show the point of view of …

via apenwarr March 18, 2019

more     (via openring)

More Posts:


  ::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact