Greenplum: Getting Checksum Errors while Offloading Data via NFS in External Tables
Article ID: 418444
Updated On:
Products
Issue/Introduction
The following checksum error is encountered when offloading data via NFS on Greenplum external tables.
SQL Error [08000]: ERROR: PXF server error : org.apache.hadoop.fs.ChecksumException: Checksum error:
Hint:
Check the PXF logs located in the /apps/greenplum/pxf/logs directory on host XXX, or set client_min_messages=LOG for additional details.
Environment
- Tanzu Greenplum (Supported Versions)
- Tanzu Greenplum Platform Extension Framework (Supported Versions)
- NFS Server & Client (Supported Versions)
Cause
This is typically not a Greenplum or PXF bug. It reflects underlying file system or network reliability issues. This error occurs when using the Greenplum Platform Extension Framework (PXF) to access or write files on a Network File System (NFS) mount during table offloading. PXF treats the NFS mount as a Hadoop-compatible file system (via the file:// protocol), where Hadoop's ChecksumFileSystem validates file integrity using CRC checksums stored in hidden .crc files. If the expected and computed checksums do not match—often at a specific byte offset, such as 0—this exception is triggered.
Common root causes include:
- File corruption or truncation: Incomplete or externally modified files may cause CRC mismatches.
- NFS configuration issues: Improper mount options (such as caching, sync settings) or inconsistent rsize/wsize.
- Hardware/network factors: Faulty cables, high latency, or bandwidth constraints affecting NFS path integrity.
Resolution
To resolve ChecksumException errors during NFS-offloaded table operations with Greenplum PXF:
- Examine logs:
- Review /apps/greenplum/pxf/logs for error details, including file paths and byte offsets.
- Validate NFS setup:
- File integrity checks:
- Ensure all data files have corresponding .crc files and that CRCs match.
- If corruption is suspected, re-copy the files to the NFS location using reliable tools (rsync, scp).
- Avoid editing data files directly on NFS—use supported transfer mechanisms.
- Network and hardware diagnostics:
- Review system logs (dmesg, syslog) for disk, NFS, or hardware issues.
- Test file transfers between alternate NFS clients/servers to help localize the problem.
- General best practices:
- For large tables, use incremental or scale-out NFS strategies, as described in Greenplum backup/offload documentation.
- Regularly monitor for file bloat and tune NFS and PXF settings for performance.
Additional Information
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