[HDFS-6698] try to optimize DFSInputStream.getFileLength()

• Type: Sub-task
• Status: Patch Available
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.0.0-alpha1
• Component/s: hdfs-client
• Labels: BB2015-05-TBR
• Assignee: Liang Xie
• Reporter: Liang Xie
• Created: 17/Jul/14 04:30
• Updated: 12/May/16 18:18

Description

HBase prefers to invoke read() serving scan request, and invoke pread() serving get reqeust. Because pread() almost holds no lock.
Let's image there's a read() running, because the definition is:

public synchronized int read

so no other read() request could run concurrently, this is known, but pread() also could not run... because:

  public int read(long position, byte[] buffer, int offset, int length)
    throws IOException {
    // sanity checks
    dfsClient.checkOpen();
    if (closed) {
      throw new IOException("Stream closed");
    }
    failures = 0;
    long filelen = getFileLength();

the getFileLength() also needs lock. so we need to figure out a no lock impl for getFileLength() before HBase multi stream feature done. [e-mail]