Structured logs, and the field that was never queried

Eleven fields on every log line, of which four have never appeared in a query.

a year of queries against the log store, by field:

  request_id     4,102 queries
  user_id        1,208
  route            902
  status           412
  duration_ms      188
  ...
  memory_peak        0
  php_version        0
  hostname           0   (one host)
  git_branch         0

four fields × 41M lines × ~20 bytes = 3.3 GB a month
of storage for information nobody has ever asked for.

A structured log invites adding fields because each one is cheap, and the cost is per line rather than per field. Removing four was uncontroversial once the query counts were visible, and the interesting one is hostname — correct to include, and useless on a single host, which is a decision that will need reversing if there is ever a second.