arrow: Fix memory leak in ColumnVector by caching decoded vector - #17738
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Every call to getArrowVector() on a dictionary-encoded column allocated a new decoded FieldVector that was never released. Since ColumnarBatch.createVectorSchemaRootFromVectors() calls it for every column of every batch, a scan over dict-encoded data leaked one vector per batch per dict-encoded column. Fix: cache the decoded vector in a private field (lazy init), and release it in close(). Repeated calls to getArrowVector() within the same batch return the same cached vector. Closes apache#17722
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Every call to
ColumnVector.getArrowVector()on a dictionary-encoded column allocates a new decodedFieldVectorthat is never released. SinceColumnarBatch.createVectorSchemaRootFromVectors()calls it for every column of every batch, a scan over dict-encoded data leaks one vector per batch per dict-encoded column, and the memory survives a fully drained and fully closed scan.Root cause
ColumnVector.getArrowVector()routes dict-encoded columns throughDictEncodedArrowConverter.toArrowVector()which allocates and populates a new vector from the reader's allocator on each call.ColumnVector.close()only closes the accessor, never the decoded vector.Fix
Cache the decoded vector in a private field, materializing it once per batch instead of on every
getArrowVector()call, and release it inclose(). Repeated calls within the same batch return the same cached vector. This matches the documented contract ("the arrow vectors are owned by the reader").Closes #17722