diff --git a/README.md b/README.md
index 6cacae5c..340cfbc2 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,7 @@
 [5. Install dependencies for PMem Shuffle](#install-dependencies-for-pmem-shuffle)  
 [6. Install PMem Shuffle for Spark](#install-pmem-shuffle-for-spark)  
 [7. PMem Shuffle for Spark Testing](#pmem-shuffle-for-spark-testing)  
+[8. Trouble Shooting](#trouble-shooting)  
 [Reference](#reference)   
 
 
@@ -134,8 +135,8 @@ installation/enabling or FW installation is out of the scope of this guide.
 6)  Step 5 is required only when running this solution over RDMA is considered.  Otherwise PMem can be initialized in fsdax mode.  
     a.  Run *ndctl create-namespace -m fsdax -r region0 -s 120g*  
     b.  Run *ndctl create-namespace -m fsdax -r region0 -s 120g*  
-    c.  Run *ndctl create-namespace -m fsdax -r region0 -s 120g*  
-    d.  Run *ndctl create-namespace -m fsdax -r region0 -s 120g*  
+    c.  Run *ndctl create-namespace -m fsdax -r region1 -s 120g*  
+    d.  Run *ndctl create-namespace -m fsdax -r region1 -s 120g*  
     Four namespaces /dev/pmem0, /dev/pmem0.1, /dev/pmem1, /dev/pmem1.1 are created. Note that the namespace name might vary due to existing namespaces. In general, the name is consistent with the pattern /dev/pmem*.     
 
     After creating the namespace in fsdax mode, the namespace is ready for a file system. Here we use Ext4 file system in enabling. 
@@ -574,6 +575,9 @@ spark.driver.rport                                              61000
 
 ```
 
+**FSDAX**
+Use `spark.shuffle.pmof.pmpool_size` to specify the size of created shuffle file. The size should obey the rule: `max(spark.shuffle.pmof.pmpool_size) < size_of_namespace * 0.9`. It's because we need to reserve some space in fsdax namespace for meta data. 
+
 **Misc**  
 The config `spark.sql.shuffle.partitions` is required to set explicitly, it's suggested to  use default value `200` unless you're pretty sure what's the meaning of this value. 
 
@@ -781,6 +785,15 @@ spark.driver.rhost                                          $IP //change to your
 spark.driver.rport                                          61000
 
 ```
+
+## <a id="trouble-shooting"></a>8. Trouble shooting
+For any reason that a previous job is failed, please empty PMem spaces before another run.  
+It's because normal space release operation might fail to be invoked for failed jobs.  
+
+For devdax, use `pmempool rm {devdax-namespace}` to reset the entire namespace.    
+For fsdax, use `rm -rf {mounted-pmem-folder}/shuffle_block*` to remove corresponding shuffle pool files.  
+
+
 ### Reference guides (without BKC access)
 -----------------------------------
 If you do not have BKC access, please following below official guide:
diff --git a/core/src/main/java/org/apache/spark/jni/pmof/JniUtils.java b/core/src/main/java/org/apache/spark/jni/pmof/JniUtils.java
index 4a9267e1..59534b2f 100644
--- a/core/src/main/java/org/apache/spark/jni/pmof/JniUtils.java
+++ b/core/src/main/java/org/apache/spark/jni/pmof/JniUtils.java
@@ -54,14 +54,20 @@ static void loadLibraryFromJar(String libName) throws IOException, IllegalAccess
   private static File moveFileFromJarToTemp(final String tmpDir, String libraryToLoad)
       throws IOException {
     final File temp = File.createTempFile(tmpDir, libraryToLoad);
-    try (final InputStream is =
-        JniUtils.class.getClassLoader().getResourceAsStream(libraryToLoad)) {
+    final InputStream is = JniUtils.class.getClassLoader().getResourceAsStream(libraryToLoad);
+    try {
       if (is == null) {
         throw new FileNotFoundException(libraryToLoad);
       } else {
         Files.copy(is, temp.toPath(), StandardCopyOption.REPLACE_EXISTING);
       }
+    }catch(Exception e){
+      e.printStackTrace();
+    }finally{
+      if (is != null){
+        is.close();
+      }
     }
-    return temp;
+  return temp;
   }
 }
diff --git a/core/src/main/java/org/apache/spark/storage/pmof/PersistentMemoryMetaHandler.java b/core/src/main/java/org/apache/spark/storage/pmof/PersistentMemoryMetaHandler.java
index fdc2a839..c47a7c5b 100644
--- a/core/src/main/java/org/apache/spark/storage/pmof/PersistentMemoryMetaHandler.java
+++ b/core/src/main/java/org/apache/spark/storage/pmof/PersistentMemoryMetaHandler.java
@@ -68,6 +68,10 @@ public void createTable(String root_dir) {
         if (fl != null) {
           fl.release();
         }
+      }catch(IOException e){
+        e.printStackTrace();
+      }
+      try{
         if (fos != null) {
           fos.close();
         }
@@ -113,6 +117,10 @@ public void insertRecord(String shuffleId, String device) {
         if (fl != null) {
           fl.release();
         }
+      }catch(IOException e){
+        e.printStackTrace();
+      }
+      try{
         if (fos != null) {
           fos.close();
         }
@@ -165,6 +173,10 @@ public String getShuffleDevice(String shuffleId){
         if (fl != null) {
           fl.release();
         }
+      }catch(IOException e){
+        e.printStackTrace();
+      }
+      try{
         if (fos != null) {
           fos.close();
         }
@@ -242,6 +254,10 @@ public String getUnusedDevice(ArrayList<String> full_device_list){
         if (fl != null) {
           fl.release();
         }
+      }catch(IOException e){
+        e.printStackTrace();
+      }
+      try{
         if (fos != null) {
           fos.close();
         }
diff --git a/native/src/PmemBuffer.h b/native/src/PmemBuffer.h
index ebb8d68a..1a30cd3c 100644
--- a/native/src/PmemBuffer.h
+++ b/native/src/PmemBuffer.h
@@ -54,7 +54,9 @@ class PmemBuffer {
         free(tmp_buf_data);
       }
       pos = remaining;
-      memcpy(buf_data + pos, pmem_data_addr, pmem_data_len);
+      if(buf_data != nullptr){
+        memcpy(buf_data + pos, pmem_data_addr, pmem_data_len);
+      }
     } else if (remaining == 0) {
 			if (buf_data_capacity < pmem_data_len) {
 				free(buf_data);
diff --git a/native/src/lib_jni_pmdk.cpp b/native/src/lib_jni_pmdk.cpp
index 9d02a33b..baf1627f 100644
--- a/native/src/lib_jni_pmdk.cpp
+++ b/native/src/lib_jni_pmdk.cpp
@@ -30,13 +30,16 @@ JNIEXPORT jlongArray JNICALL Java_org_apache_spark_storage_pmof_PersistentMemory
   uint64_t size = 0;
   pmkv->get_meta_size(key_str, &size);
   struct memory_meta* mm = (struct memory_meta*)std::malloc(sizeof(struct memory_meta));
-  mm->meta = (uint64_t*)std::malloc(size*2*sizeof(uint64_t));
-  pmkv->get_meta(key_str, mm);
-  jlongArray data = env->NewLongArray(mm->length);
-  env->SetLongArrayRegion(data, 0, mm->length, (jlong*)mm->meta);
-  std::free(mm->meta);
-  std::free(mm);
-  return data;
+  if(mm != nullptr){
+    mm->meta = (uint64_t*)std::malloc(size*2*sizeof(uint64_t));
+    pmkv->get_meta(key_str, mm);
+    jlongArray data = env->NewLongArray(mm->length);
+    env->SetLongArrayRegion(data, 0, mm->length, (jlong*)mm->meta);
+    std::free(mm->meta);
+    std::free(mm);
+    return data;
+  }
+  return nullptr;
 }
 
 JNIEXPORT jlong JNICALL Java_org_apache_spark_storage_pmof_PersistentMemoryPool_nativeGetBlockSize
@@ -61,8 +64,9 @@ JNIEXPORT jlong JNICALL Java_org_apache_spark_storage_pmof_PersistentMemoryPool_
 JNIEXPORT jint JNICALL Java_org_apache_spark_storage_pmof_PersistentMemoryPool_nativeCloseDevice
   (JNIEnv *env, jclass obj, jlong kv) {
   pmemkv *pmkv = static_cast<pmemkv*>((void*)kv);
-  pmkv->free_all();
+  long result = pmkv->free_all();
   delete pmkv;
+  return result;
 }
 
 JNIEXPORT jlong JNICALL Java_org_apache_spark_storage_pmof_PersistentMemoryPool_nativeGetRoot
@@ -110,7 +114,8 @@ JNIEXPORT jint JNICALL Java_org_apache_spark_storage_pmof_PmemBuffer_nativeWrite
 
 JNIEXPORT jint JNICALL Java_org_apache_spark_storage_pmof_PmemBuffer_nativeGetPmemBufferRemaining
   (JNIEnv *env, jobject obj, jlong pmBuffer) {
-  ((PmemBuffer*)pmBuffer)->getRemaining();
+  int remaining = ((PmemBuffer*)pmBuffer)->getRemaining();
+  return remaining;
 }
 
 JNIEXPORT jlong JNICALL Java_org_apache_spark_storage_pmof_PmemBuffer_nativeGetPmemBufferDataAddr
@@ -121,6 +126,7 @@ JNIEXPORT jlong JNICALL Java_org_apache_spark_storage_pmof_PmemBuffer_nativeGetP
 JNIEXPORT jint JNICALL Java_org_apache_spark_storage_pmof_PmemBuffer_nativeCleanPmemBuffer
   (JNIEnv *env, jobject obj, jlong pmBuffer) {
   ((PmemBuffer*)pmBuffer)->clean();
+  return 0;
 }
 
 JNIEXPORT jint JNICALL Java_org_apache_spark_storage_pmof_PmemBuffer_nativeDeletePmemBuffer
diff --git a/native/src/libjnipmdk.so b/native/src/libjnipmdk.so
new file mode 100755
index 00000000..2621a524
Binary files /dev/null and b/native/src/libjnipmdk.so differ
diff --git a/native/src/pmemkv.h b/native/src/pmemkv.h
index d7a4f606..e659e478 100644
--- a/native/src/pmemkv.h
+++ b/native/src/pmemkv.h
@@ -135,6 +135,9 @@ class pmemkv {
         return -1;
       }
       struct block_entry* bep = (struct block_entry*)pmemobj_direct(beo);
+      if (bep == nullptr){
+        return -1;
+      }
       bep->data = pmemobj_tx_zalloc(count, DATA_TYPE);
       if (bep->data.off == 0) {
         (void) pmemobj_tx_end();
@@ -156,7 +159,10 @@ class pmemkv {
       } else {
         // add the modified tail entry to the undo data
         pmemobj_tx_add_range(bp->tail, 0, sizeof(struct block_entry));
-        ((struct block_entry*)pmemobj_direct(bp->tail))->hdr.next = beo;
+        block_entry* tail_bep = (struct block_entry*)pmemobj_direct(bp->tail);
+        if (tail_bep != nullptr){
+          tail_bep->hdr.next = beo;
+        }
       }
 
       bp->tail = beo; // update tail
@@ -261,7 +267,9 @@ class pmemkv {
             //There are two or more block_entry
             bp->head = bep->hdr.next;
             block_entry* new_head_pointer = (struct block_entry*)pmemobj_direct(bp->head);
-            new_head_pointer->hdr.pre = OID_NULL;
+            if(new_head_pointer != nullptr){
+              new_head_pointer->hdr.pre = OID_NULL;
+            }
             bp->bytes_written = bp->bytes_written - bep->hdr.size;
             pmemobj_free(&bep->data);
             pmemobj_free(&cur->beo);
@@ -277,7 +285,9 @@ class pmemkv {
         if (pmemobj_direct(bep->hdr.next) == nullptr){
             //The one node scenario is already covered in head judgement, there are two or more nodes here
             struct block_entry* prebep = (struct block_entry*)pmemobj_direct(bep->hdr.pre);
-            prebep->hdr.next = OID_NULL;
+            if (prebep != nullptr){
+              prebep->hdr.next = OID_NULL;
+            }
             bp->tail = bep->hdr.pre;
             if((struct block_entry*)pmemobj_direct(bp->tail) == nullptr){
                 std::cout<<"Error. The bp->tail should not be nullptr"<<std::endl;
@@ -296,8 +306,14 @@ class pmemkv {
 
         //Node to be deleted is at the middle, no head or tail, there are at least three nodes
         struct block_entry* prebep = (struct block_entry*)pmemobj_direct(bep->hdr.pre);
+        if(prebep == nullptr){
+          return -1;
+        }
         prebep->hdr.next = bep->hdr.next;
         struct block_entry* nextbep = (struct block_entry*)pmemobj_direct(bep->hdr.next);
+        if(nextbep == nullptr){
+          return -1;
+        }
         nextbep->hdr.pre = bep->hdr.pre;
         bp->bytes_written = bp->bytes_written - bep->hdr.size;
         pmemobj_free(&bep->data);
@@ -459,6 +475,9 @@ class pmemkv {
       }
       bo = pmemobj_root(pmem_pool, sizeof(struct base));
       bp = (struct base*)pmemobj_direct(bo);
+      if(bp == nullptr){
+        return -1;
+      }
       bp->head = OID_NULL;
       bp->tail = OID_NULL;
       bp->bytes_written = 0;
@@ -478,6 +497,9 @@ class pmemkv {
       // walk through all the block entry in pmem, don't need lock here
       bo = pmemobj_root(pmem_pool, sizeof(struct base));
       bp = (struct base*)pmemobj_direct(bo);
+      if(bp == nullptr){
+        return -1;
+      }
       struct block_entry *next = (struct block_entry*)pmemobj_direct(bp->head);
       PMEMoid next_beo = bp->head;
       while (next != nullptr) {
@@ -534,6 +556,7 @@ class pmemkv {
         bm->beo = beo;
         struct block_meta_list* bml = (struct block_meta_list*)std::malloc(sizeof(block_meta_list));
         if (!bml) {
+          free(bm);
           perror("malloc error in pmemkv update_meta");
           return -1;
         }