[HADOOP-9667] SequenceFile: Reset keys and values when syncing to a place before the header

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Assignee: Unassigned
• Reporter: Colin McCabe
• Created: 24/Jun/13 16:38
• Updated: 24/Jun/13 16:38

Description

There seems to be a bug in the SequenceFile#sync function. Thanks to Christopher Ng for this report:

    /** Seek to the next sync mark past a given position.*/
    public synchronized void sync(long position) throws IOException {
      if (position+SYNC_SIZE >= end) {
        seek(end);
        return;
      }

      if (position < headerEnd) {
        // seek directly to first record
        in.seek(headerEnd);                                         <====
should this not call seek (ie this.seek) instead?
        // note the sync marker "seen" in the header
        syncSeen = true;
        return;
      }

the problem is that when you sync to the start of a compressed file, the
noBufferedKeys and valuesDecompressed isn't reset so a block read isn't
triggered. When you subsequently call next() you're potentially getting
keys from the buffer which still contains keys from the previous position
of the file.