turn off the in-memory cache on agency nodes, as it is not needed there (#6742)

CHANGELOG

@@ -12,6 +12,11 @@ devel
 v3.4.0-rc.3 (XXXX-XX-XX)
 ------------------------
 
+* disable in-memory cache for edge and traversal data on agency nodes, as it
+  is not needed there
+
+* include forward-ported diagnostic options for debugging LDAP connections
+
 * support installation of ArangoDB on Windows into directories with multibyte
   character filenames on Windows platforms that used a non-UTF8-codepage
 

arangod/Cache/CacheManagerFeature.cpp

@@ -33,6 +33,7 @@
 #include "Basics/process-utils.h"
 #include "Cache/CacheManagerFeatureThreads.h"
 #include "Cache/Manager.h"
+#include "Cluster/ServerState.h"
 #include "Logger/Logger.h"
 #include "ProgramOptions/ProgramOptions.h"
 #include "ProgramOptions/Section.h"
@@ -87,7 +88,7 @@ void CacheManagerFeature::validateOptions(
     FATAL_ERROR_EXIT();
   }
 
-  if (_cacheSize < (CacheManagerFeature::minRebalancingInterval)) {
+  if (_rebalancingInterval < (CacheManagerFeature::minRebalancingInterval)) {
     LOG_TOPIC(FATAL, arangodb::Logger::FIXME)
         << "invalid value for `--cache.rebalancing-interval', need at least "
         << (CacheManagerFeature::minRebalancingInterval);
@@ -96,6 +97,12 @@ void CacheManagerFeature::validateOptions(
 }
 
 void CacheManagerFeature::start() {
+  if (ServerState::instance()->isAgent()) {
+    // we intentionally do not activate the cache on an agency node, as it
+    // is not needed there
+    return;
+  }
+
   auto scheduler = SchedulerFeature::SCHEDULER;
   auto postFn = [scheduler](std::function<void()> fn) -> bool {
     scheduler->post(fn, false);

arangod/Cache/CacheManagerFeature.h

@@ -34,6 +34,7 @@ namespace arangodb {
 class CacheManagerFeature final
     : public application_features::ApplicationFeature {
  public:
+  // note that the cache is optional and that MANAGER can be a nullptr!
   static cache::Manager* MANAGER;
 
   explicit CacheManagerFeature(application_features::ApplicationServer& server);
@@ -57,4 +58,4 @@ class CacheManagerFeature final
 
 }
 
-#endif
+#endif

arangod/Graph/TraverserDocumentCache.cpp

@@ -44,8 +44,9 @@ using namespace arangodb::graph;
 TraverserDocumentCache::TraverserDocumentCache(aql::Query* query)
     : TraverserCache(query), _cache(nullptr) {
   auto cacheManager = CacheManagerFeature::MANAGER;
-  TRI_ASSERT(cacheManager != nullptr);
-  _cache = cacheManager->createCache(cache::CacheType::Plain);
+  if (cacheManager != nullptr) {
+    _cache = cacheManager->createCache(cache::CacheType::Plain);
+  }
 }
 
 TraverserDocumentCache::~TraverserDocumentCache() {
@@ -165,4 +166,3 @@ void TraverserDocumentCache::insertDocument(
     }
   }
 }
-

arangod/RocksDBEngine/RocksDBCollection.cpp

@@ -108,7 +108,8 @@ RocksDBCollection::RocksDBCollection(
       _cachePresent(false),
       _cacheEnabled(!collection.system() &&
                     basics::VelocyPackHelper::readBooleanValue(
-                        info, "cacheEnabled", false)) {
+                        info, "cacheEnabled", false) && 
+                    CacheManagerFeature::MANAGER != nullptr) {
   TRI_ASSERT(!ServerState::instance()->isCoordinator());
   VPackSlice s = info.get("isVolatile");
   if (s.isBoolean() && s.getBoolean()) {
@@ -139,7 +140,8 @@ RocksDBCollection::RocksDBCollection(
       _cache(nullptr),
       _cachePresent(false),
       _cacheEnabled(
-          static_cast<RocksDBCollection const*>(physical)->_cacheEnabled) {
+          static_cast<RocksDBCollection const*>(physical)->_cacheEnabled &&
+          CacheManagerFeature::MANAGER != nullptr) {
   TRI_ASSERT(!ServerState::instance()->isCoordinator());
   rocksutils::globalRocksEngine()->addCollectionMapping(
     _objectId, _logicalCollection.vocbase().id(), _logicalCollection.id()
@@ -172,7 +174,8 @@ Result RocksDBCollection::updateProperties(VPackSlice const& slice,
   auto isSys = _logicalCollection.system();
 
   _cacheEnabled = !isSys && basics::VelocyPackHelper::readBooleanValue(
-                                slice, "cacheEnabled", _cacheEnabled);
+                                slice, "cacheEnabled", _cacheEnabled) &&
+                  CacheManagerFeature::MANAGER != nullptr;
   primaryIndex()->setCacheEnabled(_cacheEnabled);
 
   if (_cacheEnabled) {

arangod/RocksDBEngine/RocksDBEngine.cpp

@@ -2056,12 +2056,22 @@ void RocksDBEngine::getStatistics(VPackBuilder& builder) const {
   }
 
   cache::Manager* manager = CacheManagerFeature::MANAGER;
-  auto rates = manager->globalHitRates();
-  builder.add("cache.limit", VPackValue(manager->globalLimit()));
-  builder.add("cache.allocated", VPackValue(manager->globalAllocation()));
-  // handle NaN
-  builder.add("cache.hit-rate-lifetime", VPackValue(rates.first >= 0.0 ? rates.first : 0.0));
-  builder.add("cache.hit-rate-recent", VPackValue(rates.second >= 0.0 ? rates.second : 0.0));
+  if (manager != nullptr) {
+    // cache turned on
+    auto rates = manager->globalHitRates();
+    builder.add("cache.limit", VPackValue(manager->globalLimit()));
+    builder.add("cache.allocated", VPackValue(manager->globalAllocation()));
+    // handle NaN
+    builder.add("cache.hit-rate-lifetime", VPackValue(rates.first >= 0.0 ? rates.first : 0.0));
+    builder.add("cache.hit-rate-recent", VPackValue(rates.second >= 0.0 ? rates.second : 0.0));
+  } else {
+    // cache turned off
+    builder.add("cache.limit", VPackValue(0));
+    builder.add("cache.allocated", VPackValue(0));
+    // handle NaN
+    builder.add("cache.hit-rate-lifetime", VPackValue(0));
+    builder.add("cache.hit-rate-recent", VPackValue(0));
+  }
 
   // print column family statistics
   builder.add("columnFamilies", VPackValue(VPackValueType::Object));

arangod/RocksDBEngine/RocksDBIndex.cpp

@@ -64,7 +64,7 @@ RocksDBIndex::RocksDBIndex(
       _cf(cf),
       _cache(nullptr),
       _cachePresent(false),
-      _cacheEnabled(useCache && !collection.system()) {
+      _cacheEnabled(useCache && !collection.system() && CacheManagerFeature::MANAGER != nullptr) {
   TRI_ASSERT(cf != nullptr && cf != RocksDBColumnFamily::definitions());
 
   if (_cacheEnabled) {
@@ -90,7 +90,7 @@ RocksDBIndex::RocksDBIndex(
       _cf(cf),
       _cache(nullptr),
       _cachePresent(false),
-      _cacheEnabled(useCache && !collection.system()) {
+      _cacheEnabled(useCache && !collection.system() && CacheManagerFeature::MANAGER != nullptr) {
   TRI_ASSERT(cf != nullptr && cf != RocksDBColumnFamily::definitions());
 
   if (_objectId == 0) {

arangod/RocksDBEngine/RocksDBTransactionState.cpp

@@ -121,8 +121,10 @@ Result RocksDBTransactionState::beginTransaction(transaction::Hints hints) {
     TRI_ASSERT(_cacheTx == nullptr);
 
     // start cache transaction
-    _cacheTx =
-        CacheManagerFeature::MANAGER->beginTransaction(isReadOnlyTransaction());
+    if (CacheManagerFeature::MANAGER != nullptr) {
+      _cacheTx =
+          CacheManagerFeature::MANAGER->beginTransaction(isReadOnlyTransaction());
+    }
 
     rocksdb::TransactionDB* db = rocksutils::globalRocksDB();
     _rocksReadOptions.prefix_same_as_start = true;  // should always be true
@@ -232,6 +234,7 @@ void RocksDBTransactionState::cleanupTransaction() noexcept {
   _rocksTransaction = nullptr;
   if (_cacheTx != nullptr) {
     // note: endTransaction() will delete _cacheTrx!
+    TRI_ASSERT(CacheManagerFeature::MANAGER != nullptr);
     CacheManagerFeature::MANAGER->endTransaction(_cacheTx);
     _cacheTx = nullptr;
   }