hhhizzz commented on code in PR #8607:
URL: https://github.com/apache/arrow-rs/pull/8607#discussion_r2443006618
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parquet/src/column/reader/decoder.rs:
##########
@@ -136,14 +134,75 @@ pub trait ColumnValueDecoder {
fn skip_values(&mut self, num_values: usize) -> Result<usize>;
}
+/// Bucket-based storage for decoder instances keyed by `Encoding`.
+///
+/// This replaces `HashMap` lookups with direct indexing to avoid hashing
overhead in the
+/// hot decoding paths.
+const ENCODING_SLOTS: usize = 10; // covers the encodings handled in `enc_slot`
+
+#[inline]
+fn enc_slot(e: Encoding) -> usize {
+ match e {
+ Encoding::PLAIN => 0,
+ Encoding::PLAIN_DICTIONARY => 2,
+ Encoding::RLE => 3,
+ #[allow(deprecated)]
+ Encoding::BIT_PACKED => 4,
+ Encoding::DELTA_BINARY_PACKED => 5,
+ Encoding::DELTA_LENGTH_BYTE_ARRAY => 6,
+ Encoding::DELTA_BYTE_ARRAY => 7,
+ Encoding::RLE_DICTIONARY => 8,
+ Encoding::BYTE_STREAM_SPLIT => 9,
+ }
+}
+
+/// Fixed-capacity storage for decoder instances keyed by Parquet encoding.
+struct DecoderBuckets<V> {
+ inner: [Option<V>; ENCODING_SLOTS],
+}
+
+impl<V> DecoderBuckets<V> {
+ #[inline]
+ fn new() -> Self {
+ Self {
+ inner: std::array::from_fn(|_| None),
+ }
+ }
+
+ #[inline]
+ fn contains_key(&self, e: Encoding) -> bool {
+ self.inner[enc_slot(e)].is_some()
+ }
+
+ #[inline]
+ fn get_mut(&mut self, e: Encoding) -> Option<&mut V> {
+ self.inner[enc_slot(e)].as_mut()
+ }
+
+ #[inline]
+ fn insert_and_get_mut(&mut self, e: Encoding, v: V) -> &mut V {
+ let slot = &mut self.inner[enc_slot(e)];
+ debug_assert!(slot.is_none());
+ *slot = Some(v);
+ slot.as_mut().unwrap()
+ }
+}
+
+impl<V> Default for DecoderBuckets<V> {
+ fn default() -> Self {
+ Self::new()
+ }
+}
+
/// An implementation of [`ColumnValueDecoder`] for `[T::T]`
pub struct ColumnValueDecoderImpl<T: DataType> {
descr: ColumnDescPtr,
current_encoding: Option<Encoding>,
- // Cache of decoders for existing encodings
- decoders: HashMap<Encoding, Box<dyn Decoder<T>>>,
+ /// Cache of decoders for existing encodings.
Review Comment:
Thank you!
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