• 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:

    Collections: The Queen’s Latin or Who Were the Romans? Part IV: The Color of Purple

    This is the fourth part (I, II, III) of our series asking the question “Who were the Romans?” and contrasting the answer we get from the historical evidence with the pop-cultural image of the Romans as a culturally and ethnically homogeneous society typic…

    via A Collection of Unmitigated Pedantry July 23, 2021

    The Leakage Problem

    I’ve spent more than ten years talking about the cost of construction of physical infrastructure, starting with subways and then branching on to other things, most. And yet there’s a problem of comparable size when discussing infrastructure waste, which, …

    via Pedestrian Observations July 23, 2021

    Songs about terrible relationships

    [Spoilers for several old musicals.] TV Tropes lists dozens of examples of the “I want” song (where the hero of a musical sings about their dream of escaping their small surroundings). After watching a bunch of musicals on maternity leave, I’m wondering h…

    via The whole sky July 17, 2021

    more     (via openring)


  • Posts
  • RSS
  • ◂◂RSS
  • Contact