Some of my design notes are up on the wiki, with a couple updates based on tweaks I made from my original plans.
Key items from the commit summary:
Major refactoring of queue handlers to support running multiple sites in one daemon.
- Initialization code moved from common.php to StatusNet class; can now switch configurations during runtime.
- As a consequence, configuration files must now be idempotent… Be careful with constant, function or class definitions.
- Control structure for daemons/QueueManager/QueueHandler has been refactored; the run loop is now managed by IoMaster run via scripts/queuedaemon.php IoManager subclasses are woken to handle socket input or polling, and may cover multiple sites.
- Plugins can implement notice queue handlers more easily by registering a QueueHandler class; no more need to add a daemon.
The new QueueDaemon runs from scripts/queuedaemon.php:
- This replaces most of the old *handler.php scripts; they’ve been refactored to the bare handler classes.
- Spawns multiple child processes to spread load; defaults to CPU count on Linux and Mac OS X systems, or override with –threads=N
- When multithreaded, child processes are automatically respawned on failure.
- Threads gracefully shut down and restart when passing a soft memory limit (defaults to 90% of memory_limit), limiting damage from memory leaks.
- Support for UDP-based monitoring: http://www.gitorious.org/snqmon
Rough control flow diagram:
|QueueDaemon ->||IoMaster ->||IoManager|
|QueueManager [listen or poll] -> QueueHandler|
|XmppManager [ping& keepalive]|
|XmppConfirmManager [poll updates]|
- Respawning features not currently available running single-threaded.
- When running single-site, configuration changes aren’t picked up.
- New sites or config changes affecting queue subscriptions are not yet handled without a daemon restart.
- SNMP monitoring output to integrate with general tools (nagios, ganglia)
- Convert XMPP confirmation message sends to use stomp queue instead of polling
- Convert xmppdaemon.php to IoManager?
- Convert Twitter status, friends import polling daemons to IoManager
- Clean up some error reporting and failure modes
- May need to adjust queue priorities for best perf in backlog/flood cases
Detailed code history available in my daemon-work branch.