Remove size limit for per-metric lookup tables

Size based cleanup was added to avoid unbounded growth of lookup tables
as metrics get deleted/reset. This should not be necessary now when lookup
tables are being reset on metric deletion.

This reverts eb1876d

README.md

@@ -106,12 +106,6 @@ section of nginx configuration.
   * `sync_interval` (number): sets the sync interval for per-worker counters and
     key index (in seconds). This sets the boundary on eventual consistency of
     counter metric increments, and metric resets/deletions. Defaults to 1.
-  * `lookup_max_size` (number): maximum size of a per-metric lookup table
-    maintained by each worker to cache full metric names. Defaults to 1000.
-    If you have metrics with extremely high cardinality and lots of available
-    RAM, you might want to increase this to avoid cache getting flushed too
-    often. Decreasing this makes sense if you have a very large number of
-    metrics or need to minimize memory usage of this library.
 
 Returns a `prometheus` object that should be used to register metrics.
 

prometheus.lua

@@ -92,9 +92,6 @@ local DEFAULT_ERROR_METRIC_NAME = "nginx_metric_errors_total"
 -- Default value for per-worker counter sync interval (seconds).
 local DEFAULT_SYNC_INTERVAL = 1
 
--- Default max size of lookup table
-local DEFAULT_LOOKUP_MAX_SIZE = 1000
-
 -- Default set of latency buckets, 5ms to 10s:
 local DEFAULT_BUCKETS = {0.005, 0.01, 0.02, 0.03, 0.05, 0.075, 0.1, 0.2, 0.3,
                          0.4, 0.5, 0.75, 1, 1.5, 2, 3, 4, 5, 10}
@@ -383,10 +380,6 @@ local function lookup_or_create(self, label_values)
       self.name, self.label_count, cnt, table_to_string(label_values))
   end
 
-  if self.lookup_size >= self.lookup_max_size then
-    self:reset_lookup()
-  end
-
   local t = self.lookup
   if label_values then
     -- Don't use ipairs here to avoid inner loop generates trace first
@@ -444,8 +437,6 @@ local function lookup_or_create(self, label_values)
   end
   t[LEAF_KEY] = full_name
 
-  self.lookup_size = self.lookup_size + 1
-
   local err = self._key_index:add(full_name, ERR_MSG_LRU_EVICTION)
   if err then
     return nil, err
@@ -625,12 +616,6 @@ local function observe(self, value, label_values)
   end
 end
 
--- Reset the metric name lookup table for a given metric.
-local function reset_lookup(self)
-  self.lookup_size = 0
-  self.lookup = {}
-end
-
 -- Delete all metrics for a given gauge, counter or a histogram.
 --
 -- This is like `del`, but will delete all time series for all previously
@@ -699,7 +684,7 @@ local function reset(self)
   end
 
   -- Clean up the full metric name lookup table as well.
-  self:reset_lookup()
+  self.lookup = {}
 end
 
 -- Initialize the module.
@@ -736,13 +721,10 @@ function Prometheus.init(dict_name, options_or_prefix)
       DEFAULT_ERROR_METRIC_NAME
     self.sync_interval = options_or_prefix.sync_interval or
       DEFAULT_SYNC_INTERVAL
-    self.lookup_max_size = options_or_prefix.lookup_max_size or
-      DEFAULT_LOOKUP_MAX_SIZE
   else
     self.prefix = options_or_prefix or ''
     self.error_metric_name = DEFAULT_ERROR_METRIC_NAME
     self.sync_interval = DEFAULT_SYNC_INTERVAL
-    self.lookup_max_size = DEFAULT_LOOKUP_MAX_SIZE
   end
 
   self.registry = {}
@@ -759,7 +741,7 @@ function Prometheus.init(dict_name, options_or_prefix)
     metric_name = ngx_re_gsub(metric_name, "_sum$", "", "jo")
     local m = self.registry[metric_name]
     if m and m.typ == TYPE_HISTOGRAM then
-      m:reset_lookup()
+      m.lookup = {}
     end
   end)
 
@@ -869,9 +851,6 @@ local function register(self, name, help, label_names, buckets, typ)
     -- ['my.net']['200'][LEAF_KEY] = 'http_count{host="my.net",status="200"}'
     -- ['my.net']['500'][LEAF_KEY] = 'http_count{host="my.net",status="500"}'
     lookup = {},
-    lookup_size = 0,
-    lookup_max_size = self.lookup_max_size,
-    reset_lookup = reset_lookup,
     parent = self,
     -- Store a reference for logging functions for faster lookup.
     _log_error = function(...) self:log_error(...) end,

prometheus_test.lua

@@ -849,44 +849,6 @@ function TestKeyIndex:testSync()
   luaunit.assertEquals(self.last_deleted_key, "key2")
 end
 
-function TestPrometheus:testLookupMaxSize()
-  local c = self.p:counter("testc", "Counter", {"tag"})
-  local g = self.p:gauge("testg", "Gauge", {"tag"})
-  local h = self.p:histogram("testh", "Histogram", {"tag"})
-
-  luaunit.assertEquals(c.lookup_size, 0)
-  luaunit.assertEquals(g.lookup_size, 0)
-  luaunit.assertEquals(h.lookup_size, 0)
-  luaunit.assertEquals(c.lookup_max_size, 1000)
-  luaunit.assertEquals(g.lookup_max_size, 1000)
-  luaunit.assertEquals(h.lookup_max_size, 1000)
-
-  for _, max_size in ipairs({10, 17, 101}) do
-    local p1 = require('prometheus').init("metrics",
-      {lookup_max_size=max_size})
-    local c1 = p1:counter("testc1", "Counter", {"tag"})
-    local g1 = p1:gauge("testg1", "Gauge", {"tag"})
-    local h1 = p1:histogram("testh1", "Histogram", {"tag"})
-
-    luaunit.assertEquals(p1.lookup_max_size, max_size)
-    luaunit.assertEquals(c1.lookup_max_size, max_size)
-    luaunit.assertEquals(g1.lookup_max_size, max_size)
-    luaunit.assertEquals(h1.lookup_max_size, max_size)
-
-    for i = 0, max_size * 2.1, 1 do
-      c1:inc(1, {tostring(i)})
-      g1:set(3, {tostring(i)})
-      h1:observe(50, {tostring(i)})
-
-      luaunit.assertEquals(c1.lookup_size, (i % max_size)+1)
-      luaunit.assertEquals(g1.lookup_size, (i % max_size)+1)
-      luaunit.assertEquals(h1.lookup_size, (i % max_size)+1)
-    end
-  end
-
-  luaunit.assertEquals(self.dict:get("nginx_metric_errors_total"), 0)
-end
-
 function TestPrometheus.testPrintfTable()
   local p = require('prometheus')
   luaunit.assertEquals(p._table_to_string(nil), "nil")