perf logging to Scuba

Summary:
Adds a new option Autoload.PerfSampleRate which enables sampled logging
of AutoloadMap and FactsStore API call latency. If the configured rate is 0,
we don't install any FactsLogger, so there is no logging overhead.

Added a new `key` column so events can be grouped by symbol or path.

Removed the old XLOG based performance logging since it doesn't provide any
good way to analyze distributions, trends, A/B tests, etc.

Differential Revision: D52539718

fbshipit-source-id: 414d7e5096de6af788c898fe6335d98f5b1cf164

Author: edwinsmith

hphp/runtime/base/runtime-option.cpp

@@ -893,6 +893,7 @@ std::string RuntimeOption::AutoloadLogging;
 bool RuntimeOption::AutoloadLoggingAllowPropagation;
 bool RuntimeOption::AutoloadRethrowExceptions = true;
 int RuntimeOption::DeclExtensionCacheSize = 500000;
+uint32_t RuntimeOption::AutoloadPerfSampleRate = 0;
 std::string RuntimeOption::FileCache;
 std::string RuntimeOption::DefaultDocument;
 std::string RuntimeOption::GlobalDocument;
@@ -2523,6 +2524,10 @@ void RuntimeOption::Load(
 
     Config::Bind(DeclExtensionCacheSize, ini, config, "Ext.Decl.CacheSize", 500000);
 
+    // Sample rate for Autoload & Facts API latency logging
+    Config::Bind(AutoloadPerfSampleRate, ini, config,
+                 "Autoload.PerfSampleRate", 0);
+
     Config::Bind(FileCache, ini, config, "Server.FileCache");
     Config::Bind(DefaultDocument, ini, config, "Server.DefaultDocument",
                  "index.php");

hphp/runtime/base/runtime-option.h

@@ -589,6 +589,7 @@ struct RuntimeOption {
   static std::string AutoloadLogging;
   static bool AutoloadLoggingAllowPropagation;
   static bool AutoloadRethrowExceptions;
+  static uint32_t AutoloadPerfSampleRate;
 
   static int DeclExtensionCacheSize;
 

hphp/runtime/ext/facts/facts-store.cpp

@@ -1189,7 +1189,10 @@ std::shared_ptr<FactsStore> make_watcher_facts(
   if (shouldSubscribe) {
     inner->subscribe();
   }
-  return FactsLogger::wrap(std::move(inner));
+  return FactsLogger::wrap(
+      std::move(inner),
+      "ext_facts watcher",
+      RuntimeOption::AutoloadPerfSampleRate);
 }
 
 std::shared_ptr<FactsStore> make_trusted_facts(
@@ -1203,7 +1206,10 @@ std::shared_ptr<FactsStore> make_trusted_facts(
   }
   auto inner = std::make_unique<FactsStoreImpl>(
       std::move(root), std::move(dbOpener), std::move(indexedMethodAttrs));
-  return FactsLogger::wrap(std::move(inner));
+  return FactsLogger::wrap(
+      std::move(inner),
+      "ext_facts trusted",
+      RuntimeOption::AutoloadPerfSampleRate);
 }
 
 } // namespace Facts