Added hinting so cache table is aware of eviction rate problems.

arangod/Cache/Cache.cpp

@@ -283,6 +283,11 @@ bool Cache::reportInsert(bool hadEviction) {
   if (((++_insertsTotal) & _evictionMask) == 0) {
     if (_insertEvictions.load() > _evictionThreshold) {
       shouldMigrate = true;
+      bool ok = _state.lock(triesGuarantee);
+      if (ok) {
+        _table->signalEvictions();
+        _state.unlock();
+      }
     }
     _insertEvictions = 0;
   }

arangod/Cache/State.h

@@ -59,12 +59,13 @@ struct State {
     locked = 0x00000001,
     blacklisted = 0x00000002,
     disabled = 0x00000004,
-    migrated = 0x00000008,
-    migrating = 0x00000010,
-    rebalancing = 0x00000020,
-    resizing = 0x00000040,
-    shutdown = 0x00000080,
-    shuttingDown = 0x00000100
+    evictions = 0x00000008,
+    migrated = 0x00000010,
+    migrating = 0x00000020,
+    rebalancing = 0x00000040,
+    resizing = 0x00000080,
+    shutdown = 0x00000100,
+    shuttingDown = 0x00000200,
   };
 
   //////////////////////////////////////////////////////////////////////////////

arangod/Cache/Table.cpp

@@ -243,7 +243,30 @@ bool Table::slotEmptied() {
           (_logSize > Table::minLogSize));
 }
 
-uint32_t Table::idealSize() const {
+void Table::signalEvictions() {
+  bool ok = _state.lock(triesGuarantee);
+  if (ok) {
+    if (!_state.isSet(State::Flag::evictions)) {
+      _state.toggleFlag(State::Flag::evictions);
+    }
+    _state.unlock();
+  }
+}
+
+uint32_t Table::idealSize() {
+  bool ok = _state.lock(triesGuarantee);
+  bool forceGrowth = false;
+  if (ok) {
+    forceGrowth = _state.isSet(State::Flag::evictions);
+    if (forceGrowth) {
+      _state.toggleFlag(State::Flag::evictions);
+    }
+    _state.unlock();
+  }
+  if (forceGrowth) {
+    return logSize() + 1;
+  }
+
   return (((static_cast<double>(_slotsUsed.load()) /
             static_cast<double>(_slotsTotal)) > Table::idealUpperRatio)
               ? (logSize() + 1)

arangod/Cache/Table.h

@@ -173,10 +173,17 @@ class Table : public std::enable_shared_from_this<Table> {
   //////////////////////////////////////////////////////////////////////////////
   bool slotEmptied();
 
+  //////////////////////////////////////////////////////////////////////////////
+  /// @brief Report that there have been too many evictions.
+  ///
+  /// Will force a subsequent idealSize() call to return a larger table size.
+  //////////////////////////////////////////////////////////////////////////////
+  void signalEvictions();
+
   //////////////////////////////////////////////////////////////////////////////
   /// @brief Returns the ideal size of the table based on fill ratio.
   //////////////////////////////////////////////////////////////////////////////
-  uint32_t idealSize() const;
+  uint32_t idealSize();
 
  private:
   static constexpr double idealLowerRatio = 0.05;