1 files changed, 160 insertions, 0 deletions
diff --git a/util/statistics.lua b/util/statistics.lua
new file mode 100644
index 00000000..39954652
--- /dev/null
+++ b/util/statistics.lua
@@ -0,0 +1,160 @@
+local t_sort = table.sort
+local m_floor = math.floor;
+local time = require "util.time".now;
+
+local function nop_function() end
+
+local function percentile(arr, length, pc)
+	local n = pc/100 * (length + 1);
+	local k, d = m_floor(n), n%1;
+	if k == 0 then
+		return arr[1] or 0;
+	elseif k >= length then
+		return arr[length];
+	end
+	return arr[k] + d*(arr[k+1] - arr[k]);
+end
+
+local function new_registry(config)
+	config = config or {};
+	local duration_sample_interval = config.duration_sample_interval or 5;
+	local duration_max_samples = config.duration_max_stored_samples or 5000;
+
+	local function get_distribution_stats(events, n_actual_events, since, new_time, units)
+		local n_stored_events = #events;
+		t_sort(events);
+		local sum = 0;
+		for i = 1, n_stored_events do
+			sum = sum + events[i];
+		end
+
+		return {
+			samples = events;
+			sample_count = n_stored_events;
+			count = n_actual_events,
+			rate = n_actual_events/(new_time-since);
+			average = n_stored_events > 0 and sum/n_stored_events or 0,
+			min = events[1] or 0,
+			max = events[n_stored_events] or 0,
+			units = units,
+		};
+	end
+
+
+	local registry = {};
+	local methods;
+	methods = {
+		amount = function (name, initial)
+			local v = initial or 0;
+			registry[name..":amount"] = function () return "amount", v; end
+			return function (new_v) v = new_v; end
+		end;
+		counter = function (name, initial)
+			local v = initial or 0;
+			registry[name..":amount"] = function () return "amount", v; end
+			return function (delta)
+				v = v + delta;
+			end;
+		end;
+		rate = function (name)
+			local since, n = time(), 0;
+			registry[name..":rate"] = function ()
+				local t = time();
+				local stats = {
+					rate = n/(t-since);
+					count = n;
+				};
+				since, n = t, 0;
+				return "rate", stats.rate, stats;
+			end;
+			return function ()
+				n = n + 1;
+			end;
+		end;
+		distribution = function (name, unit, type)
+			type = type or "distribution";
+			local events, last_event = {}, 0;
+			local n_actual_events = 0;
+			local since = time();
+
+			registry[name..":"..type] = function ()
+				local new_time = time();
+				local stats = get_distribution_stats(events, n_actual_events, since, new_time, unit);
+				events, last_event = {}, 0;
+				n_actual_events = 0;
+				since = new_time;
+				return type, stats.average, stats;
+			end;
+
+			return function (value)
+				n_actual_events = n_actual_events + 1;
+				if n_actual_events%duration_sample_interval == 1 then
+					last_event = (last_event%duration_max_samples) + 1;
+					events[last_event] = value;
+				end
+			end;
+		end;
+		sizes = function (name)
+			return methods.distribution(name, "bytes", "size");
+		end;
+		times = function (name)
+			local events, last_event = {}, 0;
+			local n_actual_events = 0;
+			local since = time();
+
+			registry[name..":duration"] = function ()
+				local new_time = time();
+				local stats = get_distribution_stats(events, n_actual_events, since, new_time, "seconds");
+				events, last_event = {}, 0;
+				n_actual_events = 0;
+				since = new_time;
+				return "duration", stats.average, stats;
+			end;
+
+			return function ()
+				n_actual_events = n_actual_events + 1;
+				if n_actual_events%duration_sample_interval ~= 1 then
+					return nop_function;
+				end
+
+				local start_time = time();
+				return function ()
+					local end_time = time();
+					local duration = end_time - start_time;
+					last_event = (last_event%duration_max_samples) + 1;
+					events[last_event] = duration;
+				end
+			end;
+		end;
+
+		get_stats = function ()
+			return registry;
+		end;
+	};
+	return methods;
+end
+
+return {
+	new = new_registry;
+	get_histogram = function (duration, n_buckets)
+		n_buckets = n_buckets or 100;
+		local events, n_events = duration.samples, duration.sample_count;
+		if not (events and n_events) then
+			return nil, "not a valid distribution stat";
+		end
+		local histogram = {};
+
+		for i = 1, 100, 100/n_buckets do
+			histogram[i] = percentile(events, n_events, i);
+		end
+		return histogram;
+	end;
+
+	get_percentile = function (duration, pc)
+		local events, n_events = duration.samples, duration.sample_count;
+		if not (events and n_events) then
+			return nil, "not a valid distribution stat";
+		end
+		return percentile(events, n_events, pc);
+	end;
+}