Improved RocksDB engine statistics with docs and rest endpoint (#2598)

* Improved statistics reporting for RocksDB engine (including cache info).

* Added documentation about db._engineStats().

* Added rest endpoint for engine stats.

Documentation/Books/Manual/DataModeling/Databases/WorkingWith.md

@@ -184,3 +184,12 @@ database. The *_system* database itself cannot be dropped.
 Databases are dropped asynchronously, and will be physically removed if
 all clients have disconnected and references have been garbage-collected.
 
+### Engine statistics
+
+retrieve statistics related to the storage engine-rocksdb
+`db._engineStats()`
+
+Returns some statistics related to storage engine activity, including figures
+about data size, cache usage, etc.
+
+**Note**: Currently this only produces useful output for the RocksDB engine.

arangod/Cache/Manager.cpp

@@ -257,7 +257,7 @@ std::pair<double, double> Manager::globalHitRates() {
   uint64_t currentHits = _findHits.load();
   uint64_t currentMisses = _findMisses.load();
   if (currentHits + currentMisses > 0) {
-    lifetimeRate = 100 * (static_cast<double>(currentHits) /
+    lifetimeRate = 100.0 * (static_cast<double>(currentHits) /
                             static_cast<double>(currentHits + currentMisses));
   }
 
@@ -278,7 +278,8 @@ std::pair<double, double> Manager::globalHitRates() {
         currentMisses = (*stats)[0].second;
       }
       if (currentHits + currentMisses > 0) {
-        windowedRate = 100 * (static_cast<double>(currentHits) /
+        windowedRate =
+            100.0 * (static_cast<double>(currentHits) /
                      static_cast<double>(currentHits + currentMisses));
       }
     }
@@ -750,8 +751,8 @@ std::shared_ptr<Manager::PriorityList> Manager::priorityList() {
   double baseWeight = std::max(minimumWeight, uniformMarginalWeight);
 #ifdef ARANGODB_ENABLE_MAINTAINER_MODE
   if (1.0 < (baseWeight * static_cast<double>(_caches.size()))) {
-    LOG_TOPIC(FATAL, Logger::FIXME) << "weight: " << baseWeight
+    LOG_TOPIC(FATAL, Logger::FIXME)
-                                    << ", count: " << _caches.size();
+        << "weight: " << baseWeight << ", count: " << _caches.size();
     TRI_ASSERT(1.0 >= (baseWeight * static_cast<double>(_caches.size())));
   }
 #endif

arangod/GeneralServer/GeneralServerFeature.cpp

@@ -443,11 +443,11 @@ void GeneralServerFeature::defineHandlers() {
                        AsyncJobManager*>,
       _jobManager.get());
 
-  _handlerFactory->addHandler(
+  _handlerFactory->addPrefixHandler(
-      "/_api/version", RestHandlerCreator<RestVersionHandler>::createNoData);
+      "/_api/engine", RestHandlerCreator<RestEngineHandler>::createNoData);
 
   _handlerFactory->addHandler(
-      "/_api/engine", RestHandlerCreator<RestEngineHandler>::createNoData);
+      "/_api/version", RestHandlerCreator<RestVersionHandler>::createNoData);
 
 #ifdef ARANGODB_ENABLE_MAINTAINER_MODE
   _handlerFactory->addHandler(

arangod/RestHandler/RestEngineHandler.cpp

@@ -38,10 +38,51 @@ RestEngineHandler::RestEngineHandler(GeneralRequest* request,
     : RestBaseHandler(request, response) {}
 
 RestStatus RestEngineHandler::execute() {
+  // extract the sub-request type
+  auto const type = _request->requestType();
+
+  if (type == rest::RequestType::GET) {
+    handleGet();
+    return RestStatus::DONE;
+  }
+
+  generateError(rest::ResponseCode::METHOD_NOT_ALLOWED,
+                TRI_ERROR_HTTP_METHOD_NOT_ALLOWED);
+  return RestStatus::DONE;
+}
+
+void RestEngineHandler::handleGet() {
+  std::vector<std::string> const& suffixes = _request->suffixes();
+
+  if (suffixes.size() > 1 || (suffixes.size() == 1 && suffixes[0] != "stats")) {
+    generateError(rest::ResponseCode::BAD, TRI_ERROR_BAD_PARAMETER,
+                  "expecting GET /_api/engine[/stats]");
+    return;
+  }
+
+  if (suffixes.size() == 0) {
+    getCapabilities();
+    return;
+  }
+
+  getStats();
+  return;
+}
+
+void RestEngineHandler::getCapabilities() {
   VPackBuilder result;
   StorageEngine* engine = EngineSelectorFeature::ENGINE;
   engine->getCapabilities(result);
 
   generateResult(rest::ResponseCode::OK, result.slice());
-  return RestStatus::DONE;
+  return;
+}
+
+void RestEngineHandler::getStats() {
+  VPackBuilder result;
+  StorageEngine* engine = EngineSelectorFeature::ENGINE;
+  engine->getStatistics(result);
+
+  generateResult(rest::ResponseCode::OK, result.slice());
+  return;
 }

arangod/RestHandler/RestEngineHandler.h

@@ -35,6 +35,11 @@ class RestEngineHandler : public arangodb::RestBaseHandler {
   char const* name() const override final { return "RestEngineHandler"; }
   bool isDirect() const override { return true; }
   RestStatus execute() override;
+
+protected:
+  void handleGet();
+  void getCapabilities();
+  void getStats();
 };
 }
 

arangod/RocksDBEngine/RocksDBEngine.cpp

@@ -34,6 +34,8 @@
 #include "Basics/VelocyPackHelper.h"
 #include "Basics/WriteLocker.h"
 #include "Basics/build.h"
+#include "Cache/CacheManagerFeature.h"
+#include "Cache/Manager.h"
 #include "GeneralServer/RestHandlerFactory.h"
 #include "Logger/Logger.h"
 #include "ProgramOptions/ProgramOptions.h"
@@ -1414,29 +1416,52 @@ RocksDBReplicationManager* RocksDBEngine::replicationManager() const {
 void RocksDBEngine::getStatistics(VPackBuilder& builder) const {
   builder.openObject();
   // add int properties
-  auto c1 = [&](std::string const& s) {
+  auto addInt = [&](std::string const& s) {
+    std::string v;
+    if (_db->GetProperty(s, &v)) {
+      int64_t i = basics::StringUtils::int64(v);
+      builder.add(s, VPackValue(i));
+    }
+  };
+  auto addStr = [&](std::string const& s) {
     std::string v;
     if (_db->GetProperty(s, &v)) {
       builder.add(s, VPackValue(v));
     }
   };
-  c1(rocksdb::DB::Properties::kNumImmutableMemTable);
+  auto addCf = [&](std::string const& name, rocksdb::ColumnFamilyHandle* c) {
-  c1(rocksdb::DB::Properties::kMemTableFlushPending);
+    std::string v;
-  c1(rocksdb::DB::Properties::kCompactionPending);
+    if (_db->GetProperty(c, rocksdb::DB::Properties::kCFStats, &v)) {
-  c1(rocksdb::DB::Properties::kBackgroundErrors);
+      builder.add(name, VPackValue(v));
-  c1(rocksdb::DB::Properties::kCurSizeActiveMemTable);
+    }
-  c1(rocksdb::DB::Properties::kCurSizeAllMemTables);
+  };
-  c1(rocksdb::DB::Properties::kSizeAllMemTables);
+  addInt(rocksdb::DB::Properties::kNumImmutableMemTable);
-  c1(rocksdb::DB::Properties::kNumEntriesImmMemTables);
+  addInt(rocksdb::DB::Properties::kMemTableFlushPending);
-  c1(rocksdb::DB::Properties::kNumSnapshots);
+  addInt(rocksdb::DB::Properties::kCompactionPending);
-  c1(rocksdb::DB::Properties::kDBStats);
+  addInt(rocksdb::DB::Properties::kBackgroundErrors);
-  c1(rocksdb::DB::Properties::kCFStats);
+  addInt(rocksdb::DB::Properties::kCurSizeActiveMemTable);
-  c1(rocksdb::DB::Properties::kSSTables);
+  addInt(rocksdb::DB::Properties::kCurSizeAllMemTables);
-  c1(rocksdb::DB::Properties::kNumRunningCompactions);
+  addInt(rocksdb::DB::Properties::kSizeAllMemTables);
-  c1(rocksdb::DB::Properties::kNumRunningFlushes);
+  addInt(rocksdb::DB::Properties::kNumEntriesImmMemTables);
-  c1(rocksdb::DB::Properties::kIsFileDeletionsEnabled);
+  addInt(rocksdb::DB::Properties::kNumSnapshots);
-  c1(rocksdb::DB::Properties::kBaseLevel);
+  addStr(rocksdb::DB::Properties::kDBStats);
-  c1(rocksdb::DB::Properties::kTotalSstFilesSize);
+  addStr(rocksdb::DB::Properties::kSSTables);
+  addInt(rocksdb::DB::Properties::kNumRunningCompactions);
+  addInt(rocksdb::DB::Properties::kNumRunningFlushes);
+  addInt(rocksdb::DB::Properties::kIsFileDeletionsEnabled);
+  addInt(rocksdb::DB::Properties::kBaseLevel);
+  addInt(rocksdb::DB::Properties::kTotalSstFilesSize);
+  builder.add("rocksdb.cfstats", VPackValue(VPackValueType::Object));
+  addCf("other", RocksDBColumnFamily::other());
+  addCf("documents", RocksDBColumnFamily::documents());
+  addCf("primary", RocksDBColumnFamily::primary());
+  addCf("edge", RocksDBColumnFamily::edge());
+  addCf("geo", RocksDBColumnFamily::geo());
+  addCf("fulltext", RocksDBColumnFamily::fulltext());
+  addCf("index", RocksDBColumnFamily::index());
+  addCf("uniqueIndex", RocksDBColumnFamily::uniqueIndex());
+  addCf("views", RocksDBColumnFamily::views());
+  builder.close();
 
   if (_options.table_factory) {
     void* options = _options.table_factory->GetOptions();
@@ -1445,6 +1470,13 @@ void RocksDBEngine::getStatistics(VPackBuilder& builder) const {
     }
   }
 
+  cache::Manager* manager = CacheManagerFeature::MANAGER;
+  auto rates = manager->globalHitRates();
+  builder.add("cache.size", VPackValue(manager->globalLimit()));
+  builder.add("cache.used", VPackValue(manager->globalAllocation()));
+  builder.add("cache.hit-rate-lifetime", VPackValue(rates.first));
+  builder.add("cache.hit-rate-recent", VPackValue(rates.second));
+
   builder.close();
 }