[HDFS-16530] setReplication debug log creates a new string even if debug is disabled

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.4.0, 3.2.4, 3.3.5
• Component/s: namenode
• Labels: pull-request-available
• Assignee: Stephen O'Donnell
• Reporter: Stephen O'Donnell
• Created: 05/Apr/22 20:50
• Updated: 06/Apr/22 16:01
• Resolved: 06/Apr/22 16:01

Description

In FSDirAttrOp, HDFS-14521 made a good change to move a noisy logger to debug:

      if (oldBR > targetReplication) {
        FSDirectory.LOG.debug("Decreasing replication from {} to {} for {}",
                             oldBR, targetReplication, iip.getPath());
      } else if (oldBR < targetReplication) {
        FSDirectory.LOG.debug("Increasing replication from {} to {} for {}",
                             oldBR, targetReplication, iip.getPath());
      } else {
        FSDirectory.LOG.debug("Replication remains unchanged at {} for {}",
                             oldBR, iip.getPath());
      }
    }

However the `iip.getPath()` method must be evaluated to pass the resulting string into the LOG.debug method, even if debug is not enabled:

This code may form a new string where it does not need to:

  public String getPath() {
    if (pathname == null) {
      pathname = DFSUtil.byteArray2PathString(path);
    }
    return pathname;
  }

We should wrap the entire logging block in `if LOG.debugEnabled()` to avoid any overhead when the logger is not enabled.

Issue Links

• links to: GitHub Pull Request #4142