Prjhub issue #5687 was fixed, but tests still need to be added.

core/src/main/java/com/orientechnologies/orient/core/config/OGlobalConfiguration.java

@@ -26,6 +26,7 @@
 import com.orientechnologies.orient.core.OConstants;
 import com.orientechnologies.orient.core.Orient;
 import com.orientechnologies.orient.core.cache.ORecordCacheWeakRefs;
+import com.orientechnologies.orient.core.engine.local.OEngineLocalPaginated;
 import com.orientechnologies.orient.core.metadata.OMetadataDefault;
 import com.orientechnologies.orient.core.serialization.serializer.record.binary.ORecordSerializerBinary;
 import com.orientechnologies.orient.core.storage.cache.local.O2QCache;
@@ -85,7 +86,27 @@ public enum OGlobalConfiguration {
       "Minimal amount of time (in seconds), since the last System.gc(), when called after tree optimization.", Long.class, 600),
 
   // STORAGE
-      DISK_CACHE_SIZE("storage.diskCache.bufferSize", "Size of disk buffer in megabytes.", Integer.class, 4 * 1024),
+  DISK_CACHE_PINNED_PAGES("storage.diskCache.pinnedPages", "Maximum amount of pinned pages which may be contained in cache,"
+      + " if this percent is reached next pages will be left in unpinned state. You can not set value more than 50", Integer.class,
+      20, false),
+
+  DISK_CACHE_SIZE("storage.diskCache.bufferSize", "Size of disk buffer in megabytes, disk size may be changed at runtime, "
+      + "but if does not enough to contain all pinned pages exception will be thrown.", Integer.class, 4 * 1024,
+      new OConfigurationChangeCallback() {
+        @Override
+        public void change(Object currentValue, Object newValue) {
+          final OEngineLocalPaginated engineLocalPaginated = (OEngineLocalPaginated) Orient.instance()
+              .getEngine(OEngineLocalPaginated.NAME);
+
+          if (engineLocalPaginated == null) {
+            OLogManager.instance().error(this,
+                "Can not change cache size in runtime because storage engine " + OEngineLocalPaginated.NAME
+                    + " was not registered");
+          } else {
+            engineLocalPaginated.changeCacheSize(((Integer) (newValue)) * 1024L * 1024L);
+          }
+        }
+      }),
 
   DISK_WRITE_CACHE_PART("storage.diskCache.writeCachePart", "Percentage of disk cache, which is used as write cache", Integer.class,
       15),
@@ -692,11 +713,11 @@ public void change(final Object iCurrentValue, final Object iNewValue) {
   private final String key;
   private final Object defValue;
   private final Class<?> type;
-  private Object value = null;
-  private String description;
-  private OConfigurationChangeCallback changeCallback = null;
-  private Boolean canChangeAtRuntime;
-  private boolean hidden = false;
+  private volatile Object value = null;
+  private final String                       description;
+  private final OConfigurationChangeCallback changeCallback;
+  private final Boolean                      canChangeAtRuntime;
+  private final boolean                      hidden;
 
   // AT STARTUP AUTO-CONFIG
   static {
@@ -706,7 +727,12 @@ public void change(final Object iCurrentValue, final Object iNewValue) {
 
   OGlobalConfiguration(final String iKey, final String iDescription, final Class<?> iType, final Object iDefValue,
       final OConfigurationChangeCallback iChangeAction) {
-    this(iKey, iDescription, iType, iDefValue, true);
+    key = iKey;
+    description = iDescription;
+    defValue = iDefValue;
+    type = iType;
+    canChangeAtRuntime = true;
+    hidden = false;
     changeCallback = iChangeAction;
   }
 
@@ -727,6 +753,7 @@ public void change(final Object iCurrentValue, final Object iNewValue) {
     type = iType;
     canChangeAtRuntime = iCanChange;
     hidden = iHidden;
+    changeCallback = null;
   }
 
   public static void dumpConfiguration(final PrintStream out) {

core/src/main/java/com/orientechnologies/orient/core/engine/local/OEngineLocalPaginated.java

@@ -20,6 +20,7 @@
 
 package com.orientechnologies.orient.core.engine.local;
 
+import java.io.IOException;
 import java.util.Map;
 
 import com.orientechnologies.common.exception.OException;
@@ -41,15 +42,26 @@ public class OEngineLocalPaginated extends OEngineAbstract {
   private final O2QCache     readCache;
 
   public OEngineLocalPaginated() {
-    readCache = new O2QCache(
-        (long) (OGlobalConfiguration.DISK_CACHE_SIZE.getValueAsLong() * 1024 * 1024 * ((100 - OGlobalConfiguration.DISK_WRITE_CACHE_PART
-            .getValueAsInteger()) / 100.0)), OGlobalConfiguration.DISK_CACHE_PAGE_SIZE.getValueAsInteger() * 1024, true);
+    readCache = new O2QCache(calculateReadCacheMaxMemory(OGlobalConfiguration.DISK_CACHE_SIZE.getValueAsLong() * 1024 * 1024),
+        OGlobalConfiguration.DISK_CACHE_PAGE_SIZE.getValueAsInteger() * 1024, true,
+        OGlobalConfiguration.DISK_CACHE_PINNED_PAGES.getValueAsInteger());
     try {
       readCache.registerMBean();
     } catch (Exception e) {
       OLogManager.instance().error(this, "MBean for read cache cannot be registered", e);
     }
+  }
+
+  private long calculateReadCacheMaxMemory(final long cacheSize) {
+    return (long) (cacheSize * ((100 - OGlobalConfiguration.DISK_WRITE_CACHE_PART.getValueAsInteger()) / 100.0));
+  }
 
+  /**
+   * @param cacheSize Cache size in bytes.
+   * @see O2QCache#changeMaximumAmountOfMemory(long)
+   */
+  public void changeCacheSize(final long cacheSize) {
+    readCache.changeMaximumAmountOfMemory(calculateReadCacheMaxMemory(cacheSize));
   }
 
   public OStorage createStorage(final String dbName, final Map<String, String> configuration) {