Demystifying the App Engine request logs

People often ask about the App Engine request logs shown in the admin console: What do all the fields mean? How should they be interpreted? They're actually fairly easy to read once you know the format, so here's a quick-reference to help.

The basic format is based on the Apache combined log format, which is so widely used even outside Apache that it's become a de-facto standard of sorts for webserver request logs. In addition to that, App Engine adds a number of extra fields logging additional, App Engine specific stats. Suppose you're examining the following log entry: - foobiz [10/May/2011:17:26:28 -0700] "GET /page.html HTTP/1.1" 500 2297 "" "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_5_8; en-us) AppleWebKit/533.19.4 (KHTML, like Gecko) Version/5.0.3 Safari/533.19.4,gzip(gfe),gzip(gfe),gzip(gfe)" "" ms=364 cpu_ms=23 api_cpu_ms=0 cpm_usd=0.001059

Here's what the fields mean, in order:

  1. Client's IP address (
  2. The RFC1413 identity of the client (in practice, always '-')
  3. The userid determined ...