Hi! I'm Julien "mezis" Letessier.

I'm a software geek: I build things with code, like web applications, platform tools, search engines, or even tiny crypto utilities.

I've had fun as an engineer, scientist, architect, manager, and start-up founder.

This is where I share about code craftsmanship, agile methods, and other random stuff I get excited about.

Running A/B tests on our hosting infrastructure

Split testing is a cornerstone of how we improve our products. While we usually run such tests for user-visible interface changes, this is an example of running a (successful!) multivariate test between CDNs.

The outcome is a 7% improvement in asset load times globally, translating into a +1% conversion on our site.

Read the full article →

Remote work: an engineering leader's perspective

A lot has been written on remote work in the software industry, most notably Jason Fried’s Remote. But many of us were left agape by the recent backlash on telecommuting by three megacompanies: Yahoo, then Reddit, the final straw being Google’s reactionary attitude on the matter.
I thought I’d share my experience as a tech lead to help spread the word: in spite of lingering 20th century management, the knowledge industry can go remote, and benefit from it.

Mine is a real-world story about successfully turning a 10-person on-site team into a 30-person distributed team. This article is a handful of factual observations, measurements, and tips from my time as HouseTrip’s head geek.

Read the full article →

Managing complexity in Go

The standard build mechanics of Go can be surprising to developers coming from other languages, sparking numerous questions like What is the standard way to organize a Go project during development?

It turns out Go packages can feel really similar to classes in object-oriented languages.
Read on for details.

Read the full article →

23 Oct
Using machine learning to rank search results (part 2)
23 Oct 2014
Using machine learning to rank search results (part 2)
17 Oct
Using machine learning to rank search results (part 1)
17 Oct 2014
Using machine learning to rank search results (part 1)
13 Oct
Pow + SSL without the hassle
13 Oct 2014
Pow + SSL without the hassle
1 Oct
Neural net training fail
1 Oct 2014
Neural net training fail
28 Sep
How I'm going to land my dream job
28 Sep 2014
How I'm going to land my dream job
23 Sep
Designing APIs in a resource-oriented architecture
23 Sep 2014
Designing APIs in a resource-oriented architecture
20 Sep
RESTful -and- fast: Representational State Notification
20 Sep 2014
RESTful -and- fast: Representational State Notification
1 Sep
Donjon, sharing passwords securely
1 Sep 2014
Donjon, sharing passwords securely
7 Apr
Document and comment code? Or don't?
7 Apr 2014
Document and comment code? Or don't?
16 Mar
Timing Rack Middlewares with metaprogramming, recursive monkey-patching, and a sprinkle of statistics
16 Mar 2014
Timing Rack Middlewares with metaprogramming, recursive monkey-patching, and a sprinkle of statistics
13 Jan
Dragonfly backed by ActiveRecord
13 Jan 2014
Dragonfly backed by ActiveRecord
6 Jan
Rebund for 4x faster Travis builds
6 Jan 2014
Rebund for 4x faster Travis builds
29 Nov
Good software comes with a good README
29 Nov 2013
Good software comes with a good README
14 Nov
Using data tiering to squeeze scale out of SQL
14 Nov 2013
Using data tiering to squeeze scale out of SQL
13 Oct
Rubinius 2.0.0 + Rbenv
13 Oct 2013
Rubinius 2.0.0 + Rbenv
26 Sep
A case of PEBKAC
26 Sep 2013
A case of PEBKAC
12 Sep
Monitoring backend services, a tale of delays and dogs
12 Sep 2013
Monitoring backend services, a tale of delays and dogs
25 Aug
Yarp, a Rubygems proxy-cache
25 Aug 2013
Yarp, a Rubygems proxy-cache
6 May
fuzzily and blurrily - two fast fuzzy-text search/match gems
6 May 2013
fuzzily and blurrily - two fast fuzzy-text search/match gems
29 Apr
mrd - MySQL in a RAMDisk for speedier tests
29 Apr 2013
mrd - MySQL in a RAMDisk for speedier tests
3 Feb
DCI in Ruby is not broken
3 Feb 2013
DCI in Ruby is not broken
28 Oct
Released git-whistles 0.6.1
28 Oct 2012
Released git-whistles 0.6.1
27 Oct
Pure CSS speech bubbles - configurable, with shadows
27 Oct 2012
Pure CSS speech bubbles - configurable, with shadows
25 Oct
Fuzzily, a Ruby gem for blazing-fast fuzzy text search
25 Oct 2012
Fuzzily, a Ruby gem for blazing-fast fuzzy text search
30 Sep
Released guignol 0.3.0
30 Sep 2012
Released guignol 0.3.0
26 Sep
Tip: Good indices in relational databases
26 Sep 2012
Tip: Good indices in relational databases
31 Aug
RFC: Donjon, a credentials server
31 Aug 2012
RFC: Donjon, a credentials server
25 Aug
Released git-whistles 0.3.1
25 Aug 2012
Released git-whistles 0.3.1
17 Aug
Where do I put my data?
17 Aug 2012
Where do I put my data?
15 Aug
Fitting output to your terminal width
15 Aug 2012
Fitting output to your terminal width
12 Aug
The case of Haml v. Erb
12 Aug 2012
The case of Haml v. Erb
11 Aug
Us craftsmens
11 Aug 2012
Us craftsmens