Add requirements doc for logging performance

docs/design/logging.md

@@ -0,0 +1,66 @@
+% Event Logging
+
+
+# Log Goals
+
+* Performance info
+* Anti-abuse
+* Load estimation
+* Game popularity
+* Debugging
+* Record for replay?
+
+
+# Log Non-Goals
+
+TO BE AVOIDED:
+
+* Capturing credentials
+* Capturing PII
+  * What identities are considered PII?
+  * Need separate very short-lifetime log for anti-abuse with extra info?
+
+
+# Configurability
+
+* Log verbosity (based on event rarity, probably)
+* Separate logs for different privacy levels?
+* Separate logs for each game individually, and for out-of-game in general?
+* Compression
+* Encryption
+
+
+# Performance Requirements
+
+* Rare events: >10ms, if non-blocking for concurrent tasks
+  * Server startup/shutdown
+  * Game plugins loaded
+  * Game create/pause/restart/quit
+  * Identity creation/modification
+* Uncommon events: >1ms if non-blocking other participants, 1ms at most if blocking
+  * Connection attempted/dropped
+  * Login attempt/success/failure
+  * Game join/leave
+  * Winloss and Gamestate changes
+* Common events: 10-100µs to keep from dominating performance
+  * Game action
+  * Game event
+  * P2P message
+  * Game state computation
+  * Game update messages
+  * Exception captured
+* Very common events: AFAP
+  * Message serialization
+  * Message transmission
+  * Message deserialization
+  * Message validation
+  * Message queuing
+  * Update rendering
+
+
+# Notes
+
+* GameEvents and game-wide updates already get pushed to all clients; they must
+  be considered recorded out of server's control already.
+* Common path should have everything needed, but NOT bloated
+  * And it should be easy (and efficient) to turn off unneeded features