Fix CHAR/VARCHAR length overflow when writing reconcile intermediate data#2390
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moomindani wants to merge 1 commit intodatabrickslabs:mainfrom
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Fix CHAR/VARCHAR length overflow when writing reconcile intermediate data#2390moomindani wants to merge 1 commit intodatabrickslabs:mainfrom
moomindani wants to merge 1 commit intodatabrickslabs:mainfrom
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Some data sources (e.g., Teradata) return CHAR(n) values with space
padding via JDBC, resulting in values that exceed the declared column
length. Delta enforces CHAR/VARCHAR length constraints through column
metadata (__CHAR_VARCHAR_TYPE_STRING), causing writes to fail for these
padded values.
Strip all column metadata via col.alias(metadata={}) before writing
intermediate DataFrames to Delta. This removes the constraint that
Delta uses for length enforcement.
Observed with Teradata via Lakehouse Federation but not with Lakebase
(PostgreSQL) via Lakehouse Federation.
Co-authored-by: Isaac
moomindani
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Changes
What does this PR do?
Strip CHAR(n)/VARCHAR(n) length constraints from DataFrames before writing intermediate data to Delta during reconciliation. This prevents
DELTA_EXCEED_CHAR_VARCHAR_LIMITerrors when source data contains space-padded CHAR values.Root cause
Some data sources (e.g., Teradata) return CHAR(n) values with space padding via JDBC, resulting in values that exceed the declared column length (e.g., a CHAR(16) column returning 16 digits + 16 spaces = 32 characters). Delta enforces CHAR/VARCHAR length constraints through column metadata (
__CHAR_VARCHAR_TYPE_STRING), causing writes to fail for these padded values.This was observed with Teradata via Lakehouse Federation but not with Lakebase (PostgreSQL) via Lakehouse Federation.
Fix
Strip all column metadata via
col.alias(name, metadata={})before writing intermediate DataFrames to Delta. This removes the constraint that Delta uses for length enforcement. The intermediate data is temporary and does not need metadata preservation.Linked issues
Fixes #2389
Tests
Test plan
test_strip_char_varchar_constraints_strips_metadata— verifies CHAR/VARCHAR metadata is strippedtest_strip_char_varchar_constraints_preserves_types— verifies column types are preserved