jasperjiaguo commented on code in PR #14883:
URL: https://github.com/apache/pinot/pull/14883#discussion_r1927455137


##########
pinot-spi/src/main/java/org/apache/pinot/spi/filesystem/LocalPinotFS.java:
##########
@@ -193,19 +200,76 @@ private static File toFile(URI uri) {
 
   private static void copy(File srcFile, File dstFile, boolean recursive)
       throws IOException {
-    if (dstFile.exists()) {
-      FileUtils.deleteQuietly(dstFile);
+    boolean oldFileExists = dstFile.exists(); // Automatically set 
oldFileExists if the old file exists
+
+    // Step 1: Calculate CRC of srcFile/directory
+    long srcCrc = calculateCrc(srcFile);
+    File backupFile = null;
+
+    if (oldFileExists) {
+      // Step 2: Rename destination file if it exists
+      backupFile = new File(dstFile.getAbsolutePath() + BACKUP);
+      if (!dstFile.renameTo(backupFile)) {
+        throw new IOException("Failed to rename destination file to backup.");
+      }
     }
-    if (srcFile.isDirectory()) {
-      if (recursive) {
-        FileUtils.copyDirectory(srcFile, dstFile);
+
+    // If any error occurs during the copy process, we want to restore the 
destination file from the backup
+    try {
+      // Step 3: Copy the file or directory
+      if (srcFile.isDirectory()) {
+        if (recursive) {
+          FileUtils.copyDirectory(srcFile, dstFile);
+        } else {
+          throw new IOException(srcFile.getAbsolutePath() + " is a directory 
and recursive copy is not enabled.");
+        }
+      } else {
+        FileUtils.copyFile(srcFile, dstFile);
+      }
+
+      // Step 4: Verify CRC of copied file
+      long dstCrc = calculateCrc(dstFile);
+      if (srcCrc != dstCrc) {
+
+        throw new IOException("CRC mismatch: source and destination files are 
not identical.");
+      }
+    } catch (IOException e) {
+      // Restore destination file from backup if copy fails
+      if (oldFileExists) {
+        if (!dstFile.delete() || !backupFile.renameTo(dstFile)) {
+          throw new IOException("Failed to restore destination file from 
backup after failed copy.");
+        }
       } else {
-        // Throws Exception on failure
-        throw new IOException(srcFile.getAbsolutePath() + " is a directory and 
recursive copy is not enabled.");
+        dstFile.delete();
+      }
+      throw e;
+    }
+
+    if (oldFileExists) {

Review Comment:
   Yes the oncall will need to potentially rename the backed up segment. 



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