In SERVER-88953, a nontrivial number of server parameters are discussed that are indicative of a developer need to support "server parameter" values via set and get commands, but only to set the value for a scope that affects the client doing the operation. Currently these are all mixed in with the true server parameters, which have a process-wide scope. This is very ad hoc and thus parameters have surprising bevavior. We're relying on global currentClient singleton of the setters and getters. I feel like this needs a comprehensive structural solution.

SERVER-88953 added opCtx to every setter, which is a tactical fix to the currentClient thread_local access concern. However it doesn't install a distinction among the different parameters as to which are client-scoped and which are global, which I feel we should do in order to reduce churn and treat these different kinds of parameters with approriate and standardized semantics.

— example current ad hoc code —

This parameter affects the whole server.

    ttlMonitorSleepSecs: 
        description: "Period of TTL monitor thread (used for testing)."
        set_at: [startup, runtime]
        cpp_vartype: AtomicWord<int>
        cpp_varname: ttlMonitorSleepSecs
        on_update: "TTLMonitor::onUpdateTTLMonitorSleepSeconds"
        default: 60
        validator: 
            gt: 0
        redact: false

Status TTLMonitor::onUpdateTTLMonitorSleepSeconds(int newSleepSeconds) {
    if (auto client = Client::getCurrent()) {
        if (auto ttlMonitor = TTLMonitor::get(client->getServiceContext())) {
            ttlMonitor->updateSleepSeconds(Seconds{newSleepSeconds});
        }
    }
    return Status::OK();
}

... But others are less clear in scope.
Because this passes an entire opCtx to writer, it could be client-specific or not.
There seems to be no way to know.

Status TicketHolderManager::updateConcurrentWriteTransactions(const int32_t& newWriteTransactions) {
    if (auto client = Client::getCurrent()) {
        auto opCtx = client->getOperationContext();
        ...
                    writer->resize(opCtx, newWriteTransactions, Date_t::max());
        ...
    }
}

https://github.com/10gen/mongo/blob/654700fe9b03de6dbe38e1d61ee9625dae064b34/src/mongo/db/admission/ticketholder_manager.cpp#L132

— the list! —
https://jira.mongodb.org/browse/SERVER-88953?focusedCommentId=7272236&focusedId=7272236&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-7272236