Troubleshooting Common Parquet File Errors and Corruption

Error 1: "Invalid Magic Number (Expected PAR1)"

Symptoms: When opening a Parquet file, your query engine throws "Invalid Parquet file: invalid magic number" or "File does not end with PAR1".

Root Cause: The Apache Parquet specification dictates that every valid file must begin and end with the 4-byte ASCII sequence "PAR1". If this error occurs, the file is almost certainly incomplete or truncated.

Fix: Verify file size against the source system. This frequently happens when an S3 multipart download is interrupted, a disk runs out of space during writing, or an HTTP transfer fails midway.

# Inspect the first and last 4 bytes of the file in terminal:
head -c 4 damaged_file.parquet
# Expected output: PAR1

tail -c 4 damaged_file.parquet
# Expected output: PAR1

Error 2: "Snappy Decompressor Stream Corrupted"

Symptoms: Querying or scanning a table fails with "snappy: corrupt input" or "decompression failed on page 4".

Root Cause: This error indicates byte corruption within the compressed data pages. Common causes include network packet corruption during raw FTP/HTTP transfers without checksum validation, or mismatched Snappy framing (raw Snappy stream vs framed Snappy format).

Fix: Re-generate the partition using Zstandard (Zstd) compression, or verify MD5/SHA256 checksums across network transfer boundaries.

Error 3: "Schema Mismatch Across Row Groups or Partitions"

Symptoms: When reading a partitioned directory of Parquet files, you encounter "Cannot merge schemas: column [user_id] has conflicting types INT32 and INT64".

Root Cause: Over time, upstream services modify data models without updating past historical files. Parquet files written before the migration contain 32-bit integers, while newly generated files contain 64-bit integers.

Fix: In DuckDB or Spark, enable schema reconciliation or cast the column explicitly during your SELECT projection.

-- In DuckDB, read partitioned datasets with automatic union of schemas:
SELECT * 
FROM read_parquet('data/year=2026/**/*.parquet', union_by_name = true);

Error 4: "Premature End of File (Truncated Footer)"

Symptoms: The file opens fine in hex editors, but libraries throw "Thrift metadata deserialization failed" or "Unexpected EOF while reading footer".

Root Cause: The file writer crashed before writing the final metadata footer block and closing the file stream.

Fix: If the footer was never written, row group offsets cannot be resolved automatically. You must regenerate the file from raw source records or restore from pipeline snapshots.

Frequently Asked Questions