diff --git a/hugegraph-core/src/main/java/com/baidu/hugegraph/task/HugeTask.java b/hugegraph-core/src/main/java/com/baidu/hugegraph/task/HugeTask.java
index 68c978a297..e9004bc129 100644
--- a/hugegraph-core/src/main/java/com/baidu/hugegraph/task/HugeTask.java
+++ b/hugegraph-core/src/main/java/com/baidu/hugegraph/task/HugeTask.java
@@ -196,10 +196,14 @@ public String toString() {
 
     @Override
     public void run() {
-        assert this.status.code() < TaskStatus.RUNNING.code();
-        if (this.checkDependenciesSuccess()) {
-            this.status(TaskStatus.RUNNING);
-            super.run();
+        try {
+            assert this.status.code() < TaskStatus.RUNNING.code();
+            if (this.checkDependenciesSuccess()) {
+                this.status(TaskStatus.RUNNING);
+                super.run();
+            }
+        } catch (Throwable e) {
+            this.setException(e);
         }
     }
 
@@ -338,7 +342,7 @@ protected Object[] asArray() {
         E.checkState(this.type != null, "Task type can't be null");
         E.checkState(this.name != null, "Task name can't be null");
 
-        List<Object> list = new ArrayList<>(24);
+        List<Object> list = new ArrayList<>(28);
 
         list.add(T.label);
         list.add(P.TASK);
diff --git a/hugegraph-core/src/main/java/com/baidu/hugegraph/task/TaskScheduler.java b/hugegraph-core/src/main/java/com/baidu/hugegraph/task/TaskScheduler.java
index ebf7639c15..6f0452a10d 100644
--- a/hugegraph-core/src/main/java/com/baidu/hugegraph/task/TaskScheduler.java
+++ b/hugegraph-core/src/main/java/com/baidu/hugegraph/task/TaskScheduler.java
@@ -196,17 +196,9 @@ public <V> void save(HugeTask<V> task) {
         this.call(() -> {
             // Construct vertex from task
             HugeVertex vertex = this.tx().constructVertex(task);
-            // Delete the old record if exist
-            Iterator<Vertex> old = this.tx().queryVertices(vertex.id());
-            if (old.hasNext()) {
-                HugeVertex oldV = (HugeVertex) old.next();
-                assert !old.hasNext();
-                if (this.tx().indexValueChanged(oldV, vertex)) {
-                    // Only delete vertex if index value changed else override
-                    this.tx().removeVertex(oldV);
-                }
-            }
-            // Do update
+            // TODO: delete index of old vertex
+            // this.tx().deleteIndex(vertex);
+            // Add or update task info in backend store, stale index might exist
             return this.tx().addVertex(vertex);
         });
     }
@@ -424,6 +416,20 @@ public boolean indexValueChanged(Vertex oldV, HugeVertex newV) {
             return false;
         }
 
+        private void deleteIndex(HugeVertex vertex) {
+            // Delete the old record if exist
+            Iterator<Vertex> old = this.queryVertices(vertex.id());
+            if (old.hasNext()) {
+                HugeVertex oldV = (HugeVertex) old.next();
+                assert !old.hasNext();
+                if (this.indexValueChanged(oldV, vertex)) {
+                    // Only delete vertex if index value changed else override
+                    // TODO: just delete index instead of removing old vertex
+                    this.removeVertex(oldV);
+                }
+            }
+        }
+
         protected void initSchema() {
             HugeGraph graph = this.graph();
             VertexLabel label = graph.schemaTransaction().getVertexLabel(TASK);
diff --git a/hugegraph-hbase/src/main/java/com/baidu/hugegraph/backend/store/hbase/HbaseOptions.java b/hugegraph-hbase/src/main/java/com/baidu/hugegraph/backend/store/hbase/HbaseOptions.java
index df3d0321ef..2937114f7c 100644
--- a/hugegraph-hbase/src/main/java/com/baidu/hugegraph/backend/store/hbase/HbaseOptions.java
+++ b/hugegraph-hbase/src/main/java/com/baidu/hugegraph/backend/store/hbase/HbaseOptions.java
@@ -56,4 +56,12 @@ public static synchronized HbaseOptions instance() {
                     rangeInt(1024, 10000),
                     2181
             );
+
+    public static final ConfigOption<Integer> HBASE_THREADS_MAX =
+            new ConfigOption<>(
+                    "hbase.threads_max",
+                    "The max threads num of hbase connections.",
+                    rangeInt(1, 1000),
+                    64
+            );
 }
diff --git a/hugegraph-hbase/src/main/java/com/baidu/hugegraph/backend/store/hbase/HbaseSessions.java b/hugegraph-hbase/src/main/java/com/baidu/hugegraph/backend/store/hbase/HbaseSessions.java
index 3f2ff14962..bcd2f969b8 100644
--- a/hugegraph-hbase/src/main/java/com/baidu/hugegraph/backend/store/hbase/HbaseSessions.java
+++ b/hugegraph-hbase/src/main/java/com/baidu/hugegraph/backend/store/hbase/HbaseSessions.java
@@ -86,6 +86,9 @@ public synchronized void open(HugeConfig conf) throws IOException {
         Configuration config = HBaseConfiguration.create();
         config.set("hbase.zookeeper.quorum", hosts);
         config.set("hbase.zookeeper.property.clientPort", String.valueOf(port));
+        // Set hbase.hconnection.threads.max 64 to avoid OOM(default value: 256)
+        config.setInt("hbase.hconnection.threads.max",
+                      conf.get(HbaseOptions.HBASE_THREADS_MAX));
 
         this.hbase = ConnectionFactory.createConnection(config);
     }