[python] Add schema short-circuit to SplitRead and FileScanner read paths#8217
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MgjLLL wants to merge 3 commits into
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[python] Add schema short-circuit to SplitRead and FileScanner read paths#8217MgjLLL wants to merge 3 commits into
MgjLLL wants to merge 3 commits into
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The schema short-circuit in FileScanner._schema_fields() returns table.table_schema.fields when schema_id matches the current schema id. The test fixture only mocked Mock(id=0) without .fields, causing the short-circuit path to return a Mock auto-attribute that is not iterable when used by SimpleStatsEvolutions._create_index_cast_mapping.
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Purpose
Fix redundant filesystem I/O in
SplitReadandFileScannerwhen reading schema.SplitReadhas 3 call sites that unconditionally callschema_manager.get_schema(schema_id)even whenschema_id == table.table_schema.id— the schema is already in memory. This causes unnecessary filesystem reads in the common case (no schema evolution).Java equivalent (
RawFileSplitRead.createFileReader()) short-circuits with:Changes
split_read.py: Add_resolve_schema()method that returns in-memory schema when id matches, replacing 3 directget_schema()calls inraw_reader_supplier,_get_fields_and_predicate, and_file_read_fieldsfile_scanner.py: Add_schema_fields()method with same short-circuit pattern forSimpleStatsEvolutionsTests
file_scanner_schema_fields_test.pywith 3 test cases covering short-circuit, delegation, and zero-id edge caseThis closes #8216