Saturday, March 28, 2009

New Lusca-head features to date

I've been adding in a few new features to Lusca.

Firstly is the config option "n_aiops_threads" which allows configuration / runtime tuning of the number of IO threads. I got fed up recompiling Lusca every time I wanted to fiddle with the number of threads, so I made it configurable.

Next is a "client_socksize" - which overrides the compiled and system default TCP socket buffer sizes for client-side sockets. This allows the admin to run Lusca with restricted client side socket buffers whilst leaving the server side socket buffers (and the default system buffer sizes) large. I'm using this on my Cacheboy CDN nodes to help scale load by having large socket buffers to grab files from the upstream servers, but smaller buffers to not waste memory on a few fast clients.

The async IO code is now in a separate library rather than in the AUFS disk storage module. This change is part of a general strategy to overhaul the disk handling code and introduce performance improvements to storage and logfile writing. I also hope to include asynchronous logfile rotation. The change breaks the "auto tuning" done via various hacks in the AUFS and COSS storage modules. Just set "n_aiops_threads" to a sensible amount (say, 8 * the number of storage directories you have, up to about 128 or so threads in total) and rely on that instead of the auto-tuning. I found the auto-tuning didn't quite work as intended anyway..

Finally, I've started exporting some of the statistics from the "info" cachemgr page in a more easier computer-parsable format. The cachemgr page "mgr:curcounters" page includes current client/server counts, current hit rates and disk/memory storage size. I'll be using these counters as part of my Cacheboy CDN statistics code.

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