OpenACS.org runs since two days on OpenACS 5.9.0. One of the benefits of OpenACS 5.9.0 are the reduced number of mutex locks during normal operations. The following values are from day averages on days with similar loads:
Mutex Locks/sec 5.8.1 5.9.0
Total 606 331
util memoize 57 14
xo_sitenodes 38 27
OpenACS.org is a low traffic site, for which these improvements are not relevant. On the production site of Learn@WU we observed of the 50k locks/sec in total during the last year, and more than 6000 locks on the util-memoize cache per seconds. Reducing theses improves scalability.