fix(nimble): Estimate Dictionary alphabet cost and PFOR exception streams as min of bit-packed and raw Trivial (#957)#957
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…eams as min of bit-packed and raw Trivial (facebookincubator#957) Summary: `DictionaryEncoding<T>::encode()` serializes the alphabet via recursive encoding selection (`encodeNested`), so the alphabet is stored with the best encoding for it -- usually bit-packed `FixedBitWidth`, not raw `Trivial`. Same case for PFOR exception streams Measured on a real MRS DataFM cluster index (exact-bit width on, all-1.0 read factors, 2000 input rows -> 11,839 KVs): 665,424,571 -> 658,483,444 bytes = -1.04%. Dictionary correctly wins more Int32/Int64 streams away from FixedBitWidth (FBW Int32 92MB->49MB, Dictionary Int32 72MB->119MB), all at smaller total size. Differential Revision: D111057748
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…eams as min of bit-packed and raw Trivial (facebookincubator#957) Summary: `DictionaryEncoding<T>::encode()` serializes the alphabet via recursive encoding selection (`encodeNested`), so the alphabet is stored with the best encoding for it -- usually bit-packed `FixedBitWidth`, not raw `Trivial`. Same case for PFOR exception streams Measured on a real MRS DataFM cluster index (exact-bit width on, all-1.0 read factors, 2000 input rows -> 11,839 KVs): 665,424,571 -> 658,483,444 bytes = -1.04%. Dictionary correctly wins more Int32/Int64 streams away from FixedBitWidth (FBW Int32 92MB->49MB, Dictionary Int32 72MB->119MB), all at smaller total size. Differential Revision: D111057748
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…eams as min of bit-packed and raw Trivial (facebookincubator#957) Summary: `DictionaryEncoding<T>::encode()` serializes the alphabet via recursive encoding selection (`encodeNested`), so the alphabet is stored with the best encoding for it -- usually bit-packed `FixedBitWidth`, not raw `Trivial`. Same case for PFOR exception streams Measured on a real MRS DataFM cluster index (exact-bit width on, all-1.0 read factors, 2000 input rows -> 11,839 KVs): 665,424,571 -> 658,483,444 bytes = -1.04%. Dictionary correctly wins more Int32/Int64 streams away from FixedBitWidth (FBW Int32 92MB->49MB, Dictionary Int32 72MB->119MB), all at smaller total size. Differential Revision: D111057748
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Summary:
DictionaryEncoding<T>::encode()serializes the alphabet via recursive encoding selection (encodeNested), so the alphabet is stored with the best encoding for it -- usually bit-packedFixedBitWidth, not rawTrivial. Same case for PFOR exception streamsMeasured on a real MRS DataFM cluster index (exact-bit width on, all-1.0 read factors, 2000 input rows -> 11,839 KVs): 665,424,571 -> 658,483,444 bytes = -1.04%. Dictionary correctly wins more Int32/Int64 streams away from FixedBitWidth (FBW Int32 92MB->49MB, Dictionary Int32 72MB->119MB), all at smaller total size.
Differential Revision: D111057748