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Why does the error 'proto: hadoop_hdfs.BlockOpResponseProto: illegal tag 0 (wire type 0)' occur in HDFS Pipelines?
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The error message:
proto: hadoop_hdfs.BlockOpResponseProto: illegal tag 0 (wire type 0)
occurs when SingleStore fails to deserialize a response from an HDFS DataNode during a data extraction operation. The message indicates that the system attempted to parse a protobuf structure but encountered an unexpected or invalid tag, indicating that the data stream does not match the expected format for BlockOpResponseProto.
There will be no exception present either in the SingleStore logs or in the HDFS logs.
Why does this happen in SingleStore?
When the system variable advanced_hdfs_pipelines is OFF (the default value), SingleStore uses a very basic library to access Hadoop and perform the extraction. This connector relies on a fundamental implementation and may not fully support the HDFS wire protocol, particularly when handling more recent or complex HDFS deployments.
The library in this case can:
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Misread or partially read a block response.
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Misalign with the protocol expected from the DataNode.
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Fail protobuf parsing — triggering the illegal tag 0 message.
This leads to extraction failure, often appearing as:
ERROR 1934 ER_EXTRACTOR_EXTRACTOR_EXTRACT: Leaf Error (...): Cannot extract data for pipeline. proto: hadoop_hdfs.BlockOpResponseProto: illegal tag 0 (wire type 0)
What does advanced_hdfs_pipelines=ON do?
When advanced_hdfs_pipelines is ON, SingleStore uses an internal client that has better compatibility with different HDFS distributions and avoids issues such as protobuf decoding failures.
The advanced pipeline correctly handles HA setups using HDFS NameNode failover mechanisms, which are not fully supported in the legacy extractor.
Native implementation provides more resilient error recovery during extraction, especially under high load or in unstable network conditions.
Ensures compatibility with newer Hadoop protocols and features that the older Java library may not handle correctly.
To enable it:
SET GLOBAL advanced_hdfs_pipelines = ON;
Reference Links
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