rednaxelafx opened a new pull request, #37252:
URL: https://github.com/apache/spark/pull/37252
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### What changes were proposed in this pull request?
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Update the `UnsafeRow` structural integrity check in `UnsafeRowUtils.
validateStructuralIntegrity` to handle a special case with null variable-length
DecimalType value.
### Why are the changes needed?
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The check should follow the format that `UnsafeRowWriter` produces. In
general, `UnsafeRowWriter` clears out a field with zero when the field is set
to be null, c.f. `UnsafeRowWriter.setNullAt(ordinal)` and
`UnsafeRow.setNullAt(ordinal)`.
But there's a special case for `DecimalType` values: this is the only type
that is both:
- can be fixed-length or variable-length, depending on the precision, and
- is mutable in `UnsafeRow`.
To support a variable-length `DecimalType` to be mutable in `UnsafeRow`, the
`UnsafeRowWriter` always leaves a 16-byte space in the variable-length section
of the `UnsafeRow` (tail end of the row), regardless of whether the `Decimal`
value being written is null or not. In the fixed-length part of the field, it
would be an "OffsetAndSize", and the `offset` part always points to the start
offset of the variable-length part of the field, while the `size` part will
either be `0` for the null value, or `1` to at most `16` for non-null values.
When `setNullAt(ordinal)` is called instead of passing a null value to
`write(int, Decimal, int, int)`, however, the `offset` part gets zero'd out and
this field stops being mutable. There's a comment on `UnsafeRow.setDecimal`
that mentions to keep this field able to support updates, `setNullAt(ordinal)`
cannot be called, but there's no code enforcement of that.
So we need to recognize that in the structural integrity check and allow
variable-length `DecimalType` to have non-zero field even for null.
Note that for non-null values, the existing check does conform to the format
from `UnsafeRowWriter`. It's only null value of variable-length `DecimalType`
that'd trigger a bug, which can affect Structured Streaming's checkpoint file
read where this check is applied.
### Does this PR introduce _any_ user-facing change?
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Yes, previously the `UnsafeRow` structural integrity validation will return
false positive for correct data, when there's a null value in a variable-length
`DecimalType` field. The fix will no longer return false positive.
Because the Structured Streaming checkpoint file validation uses this check,
previously a good checkpoint file may be rejected by the check, and the only
workaround is to disable the check; with the fix, the correct checkpoint file
will be allowed to load.
### How was this patch tested?
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Added new test case in `UnsafeRowUtilsSuite`
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