Tunables in config

Claim: a value someone will set (a quota, a threshold, a price) lives in a configuration file, read at run time, and a value nobody has measured yet is tagged PROVISIONAL.

• Grade: supported with caveat for one place for a value that will change, from information hiding; the PROVISIONAL tag is a convention: tagged shortcuts are measured as common and often left, not as helpful.
• Evidence: against (configuration).
• Check: provisional-tags: a tag older than 90 days becomes a question; whether a value belongs in config is judgment.
• Reader styles: none override it.

What it asks

• A value goes to config only when someone other than its author will set it, or will set it at a different time. Otherwise it is a named constant in the code.
• Every config value says what it controls and where its number came from.
• A guess is tagged PROVISIONAL, and the tag is removed only with a measurement.

Why

A decision likely to change is hidden behind one place (Parnas 1972). Tagging a known shortcut is a studied practice: self-admitted technical debt appeared in 2.4% to 31% of files in four projects (Potdar 2014).

Limits

Every parameter costs. Only 6.1% to 16.7% of parameters were set by most users and up to 54.1% were seldom set, and a commercial system could drop 51.9% of its parameters (Xu 2015). Most real misconfigurations are parameter mistakes (Yin 2011).

Tags pile up: only 26.3% to 63.5% of tagged debt was later removed (Potdar 2014). No study here tests whether a tagged guess is measured sooner than an untagged one.

Practice also keeps such values in the environment: the Twelve-Factor App does so (Wiggins 2011, convention). This review found no study comparing the two; the evidence above is about configuration files.