[IMPALA-10005] Impala can't read Snappy compressed text files on S3 or ABFS

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: Impala 4.0.0
• Fix Version/s: Impala 4.0.0
• Component/s: Frontend
• Target Version: Impala 4.0.0
• Epic Color: ghx-label-5
• Assignee: Joe McDonnell
• Reporter: Joe McDonnell
• Created: 24/Jul/20 01:27
• Updated: 06/Aug/20 20:16
• Resolved: 06/Aug/20 20:16

Description

When reading snappy compressed text from S3 or ABFS on a release build, it fails to decompress:

 

I0723 21:19:43.712909 229706 status.cc:128] Snappy: RawUncompress failed
    @           0xae26c9  impala::Status::Status()
    @          0x107635b  impala::SnappyDecompressor::ProcessBlock()
    @          0x11b1f2d  impala::HdfsTextScanner::FillByteBufferCompressedFile()
    @          0x11b23ef  impala::HdfsTextScanner::FillByteBuffer()
    @          0x11af96f  impala::HdfsTextScanner::FillByteBufferWrapper()
    @          0x11b096b  impala::HdfsTextScanner::ProcessRange()
    @          0x11b2b31  impala::HdfsTextScanner::GetNextInternal()
    @          0x118644b  impala::HdfsScanner::ProcessSplit()
    @          0x11774c2  impala::HdfsScanNode::ProcessSplit()
    @          0x1178805  impala::HdfsScanNode::ScannerThread()
    @          0x1100f31  impala::Thread::SuperviseThread()
    @          0x1101a79  boost::detail::thread_data<>::run()
    @          0x16a3449  thread_proxy
    @     0x7fc522befe24  start_thread
    @     0x7fc522919bac  __clone

When using a debug build, Impala hits the following DCHECK:

 

 

F0723 23:45:12.849973 249653 hdfs-text-scanner.cc:197] Check failed: stream_>file_desc()>file_compression != THdfsCompression::SNAPPY FE should have generated SNAPPY_BLOCKED instead.

That DCHECK explains why it would fail to decompress. It is using the wrong THdfsCompression.

I reproduced this on master in my dev env by changing FileSystemUtil::supportsStorageIds() to always return true. This emulates the behavior on object stores like S3 and ABFS.

 

  /**
   * Returns true if the filesystem supports storage UUIDs in BlockLocation calls.
   */
  public static boolean supportsStorageIds(FileSystem fs) {
    return false;
  }

This is specific to Snappy and does not appear to apply to other compression codecs.