Re: [PR] HDDS-13083. Handle cases where block deletion generates tree file before scanner [ozone]

["aswinshakil (via GitHub)" <gi...@apache.org>]

aswinshakil commented on code in PR #8565:
URL: https://github.com/apache/ozone/pull/8565#discussion_r2137314833


##########
hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/checksum/ContainerChecksumTreeManager.java:
##########
@@ -395,6 +385,7 @@ public ByteString getContainerChecksumInfo(KeyValueContainerData data) throws IO
    * Callers are not required to hold a lock while calling this since writes are done to a tmp file and atomically
    * swapped into place.
    */
+  // TODO HDDS-12824 Once data checksum is stored in RocksDB this method can be removed.

Review Comment:
   Not related to this patch, but we can use this function to create a debug tool to read the on-disk `.tree` file. Right now, it is only readable by the reconciliation process. A debug tool would be helpful. 



##########
hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/checksum/ContainerChecksumTreeManager.java:
##########
@@ -329,21 +306,34 @@ private Lock getLock(long containerID) {
   }
 
   /**
+   * Reads the checksum info of the specified container. If the tree file with the information does not exist, an empty
+   * instance is returned.
    * Callers are not required to hold a lock while calling this since writes are done to a tmp file and atomically
    * swapped into place.
    */
-  public Optional<ContainerProtos.ContainerChecksumInfo> read(ContainerData data) throws IOException {
+  public ContainerProtos.ContainerChecksumInfo read(ContainerData data) throws IOException {
     try {
-      return captureLatencyNs(metrics.getReadContainerMerkleTreeLatencyNS(), () -> readChecksumInfo(data));
+      return captureLatencyNs(metrics.getReadContainerMerkleTreeLatencyNS(), () ->
+          readChecksumInfo(data).orElse(ContainerProtos.ContainerChecksumInfo.newBuilder().build()));
     } catch (IOException ex) {
       metrics.incrementMerkleTreeReadFailures();
-      throw new IOException(ex);
+      throw ex;
     }
   }
 
-  private Optional<ContainerProtos.ContainerChecksumInfo.Builder> readBuilder(ContainerData data) throws IOException {
-    Optional<ContainerProtos.ContainerChecksumInfo> checksumInfo = read(data);
-    return checksumInfo.map(ContainerProtos.ContainerChecksumInfo::toBuilder);
+  /**
+   * Reads the checksum info of the specified container. If the tree file with the information does not exist, or there
+   * is an exception trying to read the file, an empty instance is returned.
+   */
+  private ContainerProtos.ContainerChecksumInfo readOrCreate(ContainerData data) {
+    try {
+      // If the file is not present, we will create the data for the first time. This happens under a write lock.

Review Comment:
   We already have this comment here. We can remove the redundant comments where this function is called. 



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