[GitHub] [carbondata] jackylk commented on a change in pull request #3459: [CARBONDATA-3582] support table status file backup

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jackylk commented on a change in pull request #3459: [CARBONDATA-3582] support table status file backup
URL: https://github.com/apache/carbondata/pull/3459#discussion_r347121421
 
 

 ##########
 File path: core/src/main/java/org/apache/carbondata/core/statusmanager/SegmentStatusManager.java
 ##########
 @@ -526,40 +539,79 @@ private static Integer compareDateValues(Long loadValue, Long userValue) {
   }
 
   /**
-   * writes load details into a given file at @param dataLoadLocation
+   * Backup the table status file as 'filename.backup'
+   * @param tableStatusPath table status file path
+   */
+  private static void backupTableStatus(String tableStatusPath) throws IOException {
+    CarbonFile file = FileFactory.getCarbonFile(tableStatusPath);
+    if (file.exists()) {
+      String backupPath = tableStatusPath + ".backup";
+      String currentContent = readFileAsString(tableStatusPath);
+      if (currentContent != null) {
+        writeStringIntoFile(backupPath, currentContent);
+      }
+    }
+  }
+
+  /**
+   * writes load details to specified path
    *
-   * @param dataLoadLocation
-   * @param listOfLoadFolderDetailsArray
-   * @throws IOException
+   * @param tableStatusPath path of the table status file
+   * @param listOfLoadFolderDetailsArray segment metadata
+   * @throws IOException if IO errors
    */
-  public static void writeLoadDetailsIntoFile(String dataLoadLocation,
+  public static void writeLoadDetailsIntoFile(
+      String tableStatusPath,
       LoadMetadataDetails[] listOfLoadFolderDetailsArray) throws IOException {
-    AtomicFileOperations fileWrite =
-        AtomicFileOperationFactory.getAtomicFileOperations(dataLoadLocation);
+    // When overwriting table status file, if process crashed, table status file
+    // will be in corrupted state. This can happen in an unstable environment,
+    // like in the cloud. To prevent the table corruption, user can enable following
+    // property to enable backup of the table status before overwriting it.
+    if (CarbonProperties.isEnableTableStatusBackup()) {
+      backupTableStatus(tableStatusPath);
+    }
+    String content = new Gson().toJson(listOfLoadFolderDetailsArray);
+    mockForTest();
+    // If process crashed during following write, table status file need to be
+    // manual recovered.
+    writeStringIntoFile(tableStatusPath, content);
+  }
+
+  // a dummy func for mocking in testcase, which simulates IOException
+  private static void mockForTest() throws IOException {
+  }
+
+  /**
+   * writes string content to specified path
+   *
+   * @param filePath path of the file to write
+   * @param content content to write
+   * @throws IOException if IO errors
+   */
+  private static void writeStringIntoFile(String filePath, String content) throws IOException {
+    AtomicFileOperations fileWrite = AtomicFileOperationFactory.getAtomicFileOperations(filePath);
     BufferedWriter brWriter = null;
     DataOutputStream dataOutputStream = null;
-    Gson gsonObjectToWrite = new Gson();
-    // write the updated data into the metadata file.
-
     try {
       dataOutputStream = fileWrite.openForWrite(FileWriteOperation.OVERWRITE);
-      brWriter = new BufferedWriter(new OutputStreamWriter(dataOutputStream,
-              Charset.forName(DEFAULT_CHARSET)));
-
-      String metadataInstance = gsonObjectToWrite.toJson(listOfLoadFolderDetailsArray);
-      brWriter.write(metadataInstance);
+      brWriter = new BufferedWriter(new OutputStreamWriter(
+          dataOutputStream, Charset.forName(CarbonCommonConstants.DEFAULT_CHARSET)));
+      brWriter.write(content);
     } catch (IOException ioe) {
-      LOG.error("Error message: " + ioe.getLocalizedMessage());
+      LOG.error("Write file failed: " + ioe.getLocalizedMessage());
 
 Review comment:
   This exception will be logged, it is thrown at line 604

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