[YARN-2996] Refine fs operations in FileSystemRMStateStore and few fixes

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.7.0
• Component/s: resourcemanager
• Target Version/s: 2.7.0
• Hadoop Flags: Reviewed
• Assignee: Yi Liu
• Reporter: Yi Liu
• Created: 30/Dec/14 06:15
• Updated: 10/Apr/15 20:10
• Resolved: 08/Jan/15 17:50

Description

In FileSystemRMStateStore, we can refine some fs operations to improve performance:
1. There are several places invoke fs.exists, then fs.getFileStatus, we can merge them to save one RPC call

if (fs.exists(versionNodePath)) {
    FileStatus status = fs.getFileStatus(versionNodePath);

2.

protected void updateFile(Path outputPath, byte[] data) throws Exception {
  Path newPath = new Path(outputPath.getParent(), outputPath.getName() + ".new");
  // use writeFile to make sure .new file is created atomically
  writeFile(newPath, data);
  replaceFile(newPath, outputPath);
}

The updateFile is not good too, it write file to output_file.tmp, then rename to output_file.new, then rename it to output_file, we can reduce one rename operation.

Also there is one unnecessary import, we can remove it.

Issue Links

• is duplicated by: YARN-3004 Fix missed synchronization in MemoryRMStateStore