An October 5 engineering account, newly selected here, describes changes to Aria, Jane Street’s internal message bus. Indexed recovery avoids scanning the entire recent stream for each subscriber. The tip-indexing code is in production; the article’s detailed performance section reports roughly 30% lower CPU use in some staging scenarios. A separate adaptive disk-splitting change remained in staging when published. The work couples experimentation with ordering/content tests and Antithesis. Its relevance is the uneven workload: a small subscription can become expensive when physically grouped with a much busier topic. Jane Street