LuciferYang opened a new pull request, #58409:
URL: https://github.com/apache/spark/pull/58409
### What changes were proposed in this pull request?
`AvroDeserializer` now takes the schema its Catalyst schema was projected
from, and under `positionalFieldMatching` it resolves a Catalyst field against
that field's position in the data schema rather than its position in the
projection. `AvroUtils.AvroSchemaHelper` takes the resulting positions; with
none it keeps using a field's own position, which is what every caller whose
Catalyst schema is not a projection needs (`from_avro`, the write path, the
state-store encoder).
The three read call sites pass the data schema: `AvroPartitionReaderFactory`
on the V2 path, `AvroFileFormat.buildReader` and `AvroFileFormat.readArchive`
on V1. A nested record keeps resolving by its own positions, since neither read
path prunes nested fields: `FileScanBuilder.supportsNestedSchemaPruning` is
false and `AvroScanBuilder` does not override it, and
`SchemaPruning.canPruneDataSchema` covers only Parquet and ORC.
ORC already does this for `orc.force.positional.evolution`:
`OrcUtils.requestedColumnIds` maps the required schema through
`dataSchema.fieldIndex(name)`, which makes its positional path
projection-independent. Avro decodes the whole record whatever the projection
asks for, so nothing extra is read.
#58340 (SPARK-57205) withholds the `SCAN_MERGING` capability from
`AvroTable` under this option, because scan merging widens the projection and
would make the wrong value visible in a new place. That gate can be dropped
once this is in.
One shape stays broken, with or without this change:
`recursiveFieldMaxDepth` makes `SchemaConverters` drop a field it will not
recurse into, so the data schema is a gapped view of the Avro schema and
positional matching misaligns from the gap onwards. The code records that where
the positions are computed.
### Why are the changes needed?
With `positionalFieldMatching=true` the deserializer is built from the
projected read schema while the Avro side stays the full Avro schema, and
`AvroUtils.AvroSchemaHelper.getAvroField` pairs Catalyst field *i* with Avro
field *i*, so a column-pruned read takes the wrong Avro field and returns wrong
values with no error. Measured on a file whose fields `a`, `b`, `c` hold `id`,
`100 * id`, `10000 * id` for ids 0 to 4, read with the option on:
```
sql("SELECT sum(a), sum(b), sum(c) FROM t").show() // 10, 1000, 100000 --
all correct
sql("SELECT sum(c) FROM t").show() // 10 -- should be
100000
sql("SELECT sum(b) FROM t").show() // 10 -- should be
1000
sql("SELECT sum(a), sum(c) FROM t").show() // 10, 1000 -- sum(c)
should be 100000
```
Only a projection that is a prefix of the file's field list comes back
right, so a column's value depends on which other columns the query selects.
Both read paths behave the same way. Whether the failure is silent depends on
the types of the mispaired fields: matching types return wrong values, as
above, and incompatible ones fail the read with a schema-incompatibility error
instead. A pushed filter is evaluated inside the deserializer, so the wrong
pairing can also drop rows rather than only return wrong values for them.
### Does this PR introduce _any_ user-facing change?
Yes, a bug fix on the Avro read path, both V1 and V2. A read that sets
`positionalFieldMatching` and prunes columns now returns the values of the
columns it asked for. A query whose projection is a prefix of the Avro field
list is unaffected, which is why the option's existing tests need no change.
The "Cannot find field at position N" message that positional matching raises
now names the position it looked for rather than the position within the
projection, which are the same number for an unprojected read. Nothing changes
when the option is off, which is the default, and nothing changes on the write
path or in `from_avro`.
### How was this patch tested?
Five new tests in `AvroSuite`, so each runs on both read paths
(`AvroV1Suite` and `AvroV2Suite` extend it): the renamed-schema shape from the
description, with every one-column and two-column projection, a pushed filter
under both settings of `spark.sql.avro.filterPushdown.enabled`, `count(1)`, and
mixed-case names under both case-sensitivity settings; a partition column
sitting between two data columns in the schema; a nested record, which must
keep resolving by its own positions, together with the `avroSchema` option
supplying the Avro side; a projection that reaches past the end of the Avro
schema, which reads null; and a mispaired type, which fails the read rather
than returning a neighbouring field's values. One test in
`AvroSchemaHelperSuite` for the helper itself, and one in
`AvroArchiveReadBase`, which runs in the tar, zip and 7z suites, because the
archive reader builds its own deserializer per entry.
Mutation check: with the position mapping disabled, all ten of the
`AvroSuite` cases fail (five on each path) and so does the archive one. The two
columns in the archive test have different types on purpose, so a wrong pairing
fails the read there rather than returning plausible values.
Regression: the whole `avro` module, 500 tests, and
`RocksDBStateEncoderSuite` plus `StateStoreSuite`, 840 tests, because the
state-store encoder builds an `AvroDeserializer` too, plus `avro/scalastyle`,
`avro/Test/scalastyle` and `sql/scalastyle`. The existing
`positionalFieldMatching` tests (SPARK-34365) needed no change, because their
projections cover the whole schema.
### Was this patch authored or co-authored using generative AI tooling?
Generated-by: Claude Code
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