Push notifications delayed, Hearbeat Interval not reliable – Google Product Forums
Good thread on GCM notifications and their interactions with NAT — they are delivered over a single TCP connection to port 5228 to the google servers, kept alive, and NAT timeouts can hang the conn resulting in delayed notifications. Particularly useful is the *#*#426#*#* dial code, which displays a log screen on Android devices with GCM debugging info.
USE Method: Linux Performance Checklist
Really late in bookmarking this, but has some up-to-date sample commandlines for sar, mpstat and iostat on linux
(tags: linux sar iostat mpstat cli ops sysadmin performance tuning use metrics)