prestodb/presto · error · UnsupportedOperationException

Error decoding values in encoding:

Error message

Error decoding  values in encoding: 

What it means

Base-class sentinel in ParquetEncoding.getValuesReader: this encoding subclass does not implement a plain values reader (it is dictionary-only or a level-only encoding), so the call is an API misuse — the reader should have initialized the dictionary instead. Not triggered by file contents.

Source

Thrown at presto-parquet/src/main/java/com/facebook/presto/parquet/ParquetEncoding.java:226

            default:
                throw new ParquetDecodingException("Unsupported  values type: " + valuesType);
        }
    }

    public boolean usesDictionary()
    {
        return false;
    }

    public Dictionary initDictionary(ColumnDescriptor descriptor, DictionaryPage dictionaryPage)
            throws IOException
    {
        throw new UnsupportedOperationException(" Dictionary encoding is not supported for: " + name());
    }

    public ValuesReader getValuesReader(ColumnDescriptor descriptor, ValuesType valuesType)
    {
        throw new UnsupportedOperationException("Error decoding  values in encoding: " + this.name());
    }

    public ValuesReader getDictionaryBasedValuesReader(ColumnDescriptor descriptor, ValuesType valuesType, Dictionary dictionary)
    {
        throw new UnsupportedOperationException(" Dictionary encoding is not supported for: " + name());
    }
}

View on GitHub (pinned to 55bb57d202)

Solutions

1. Call initDictionary and getDictionaryBasedValuesReader for dictionary encodings
2. Guard with usesDictionary() before choosing the reader path
3. Fix reader branching logic in the calling code

When it happens

Trigger: Thrown at presto-parquet/src/main/java/com/facebook/presto/parquet/ParquetEncoding.java:226 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of prestodb/presto@55bb57d202 (2026-09-04). Data as JSON: /api/errors/25559bf32a0f093c. Report an issue: GitHub.