ACT-2096: Deadlock while concurrently finishing process instances on MSSQL

Delete operations optimization is now disabled by default and can be enabled in config

modules/activiti-engine/src/main/java/org/activiti/engine/impl/cfg/ProcessEngineConfigurationImpl.java

@@ -104,6 +104,7 @@ import org.activiti.engine.impl.calendar.DurationBusinessCalendar;
 import org.activiti.engine.impl.calendar.MapBusinessCalendarManager;
 import org.activiti.engine.impl.cfg.standalone.StandaloneMybatisTransactionContextFactory;
 import org.activiti.engine.impl.db.DbIdGenerator;
+import org.activiti.engine.impl.db.DbSqlSession;
 import org.activiti.engine.impl.db.DbSqlSessionFactory;
 import org.activiti.engine.impl.db.IbatisVariableTypeHandler;
 import org.activiti.engine.impl.delegate.DefaultDelegateInterceptor;
@@ -381,6 +382,16 @@ public abstract class ProcessEngineConfigurationImpl extends ProcessEngineConfig
   protected int batchSizeProcessInstances = 25;
   protected int batchSizeTasks = 25;
   
+  /**
+   * Experimental setting. Default is false.
+   * 
+   * If set to true, in the {@link DbSqlSession} during the handling of delete operations,
+   * those operations of the same type are merged together. 
+   * (eg if you have two 'DELETE from X where id=Y' and 'DELETE from X where id=W', it will be merged
+   * into one delete statement 'DELETE from X where id=Y or id=W'.
+   */
+  protected boolean isOptimizeDeleteOperationsEnabled;
+  
   protected boolean enableEventDispatcher = true;
   protected ActivitiEventDispatcher eventDispatcher;
   protected List<ActivitiEventListener> eventListeners;
@@ -755,6 +766,7 @@ public abstract class ProcessEngineConfigurationImpl extends ProcessEngineConfig
       dbSqlSessionFactory.setTablePrefixIsSchema(tablePrefixIsSchema);
       dbSqlSessionFactory.setDatabaseCatalog(databaseCatalog);
       dbSqlSessionFactory.setDatabaseSchema(databaseSchema);
+      dbSqlSessionFactory.setOptimizeDeleteOperationsEnabled(isOptimizeDeleteOperationsEnabled);
       addSessionFactory(dbSqlSessionFactory);
       
       addSessionFactory(new GenericManagerFactory(AttachmentEntityManager.class));

modules/activiti-engine/src/main/java/org/activiti/engine/impl/db/DbSqlSession.java

@@ -120,9 +120,12 @@ public class DbSqlSession implements Session {
   protected List<DeserializedObject> deserializedObjects = new ArrayList<DeserializedObject>();
   protected String connectionMetadataDefaultCatalog;
   protected String connectionMetadataDefaultSchema;
+  
+  protected boolean isOptimizeDeleteOperationsEnabled;
 
   public DbSqlSession(DbSqlSessionFactory dbSqlSessionFactory) {
     this.dbSqlSessionFactory = dbSqlSessionFactory;
+    this.isOptimizeDeleteOperationsEnabled = dbSqlSessionFactory.isOptimizeDeleteOperationsEnabled();
     this.sqlSession = dbSqlSessionFactory
       .getSqlSessionFactory()
       .openSession();
@@ -634,7 +637,7 @@ public class DbSqlSession implements Session {
   protected List<DeleteOperation> optimizeDeleteOperations(List<DeleteOperation> deleteOperations) {
   	
   	// No optimization possible for 0 or 1 operations
-  	if (deleteOperations.size() <= 1) {
+  	if (!isOptimizeDeleteOperationsEnabled || deleteOperations.size() <= 1) {
   		return deleteOperations;
   	}
   	
@@ -1436,5 +1439,12 @@ public class DbSqlSession implements Session {
     return dbSqlSessionFactory;
   }
 
+	public boolean isOptimizeDeleteOperationsEnabled() {
+		return isOptimizeDeleteOperationsEnabled;
+	}
 
+	public void setOptimizeDeleteOperationsEnabled(boolean isOptimizeDeleteOperationsEnabled) {
+		this.isOptimizeDeleteOperationsEnabled = isOptimizeDeleteOperationsEnabled;
+	}
+  
 }

modules/activiti-engine/src/main/java/org/activiti/engine/impl/db/DbSqlSessionFactory.java

@@ -176,6 +176,7 @@ public class DbSqlSessionFactory implements SessionFactory {
   protected Map<Class<?>,String>  selectStatements = new ConcurrentHashMap<Class<?>, String>();
   protected boolean isDbIdentityUsed = true;
   protected boolean isDbHistoryUsed = true;
+  protected boolean isOptimizeDeleteOperationsEnabled;
 
 
   public Class< ? > getSessionType() {
@@ -373,5 +374,13 @@ public class DbSqlSessionFactory implements SessionFactory {
 	public boolean isTablePrefixIsSchema() {
 	  return tablePrefixIsSchema;
   }
+
+	public boolean isOptimizeDeleteOperationsEnabled() {
+		return isOptimizeDeleteOperationsEnabled;
+	}
+
+	public void setOptimizeDeleteOperationsEnabled(boolean isOptimizeDeleteOperationsEnabled) {
+		this.isOptimizeDeleteOperationsEnabled = isOptimizeDeleteOperationsEnabled;
+	}
 	
 }