diff --git a/parquet/src/basic.rs b/parquet/src/basic.rs
index bd42f043eead..7f50eada46de 100644
--- a/parquet/src/basic.rs
+++ b/parquet/src/basic.rs
@@ -771,6 +771,11 @@ impl EncodingMask {
         Self(mask)
     }
 
+    /// Mark the given [`Encoding`] as present in this mask.
+    pub fn insert(&mut self, val: Encoding) {
+        self.0 |= 1 << (val as i32);
+    }
+
     /// Test if a given [`Encoding`] is present in this mask.
     pub fn is_set(&self, val: Encoding) -> bool {
         self.0 & (1 << (val as i32)) != 0
diff --git a/parquet/src/column/reader/decoder.rs b/parquet/src/column/reader/decoder.rs
index acf4827ed538..1d4e2f751181 100644
--- a/parquet/src/column/reader/decoder.rs
+++ b/parquet/src/column/reader/decoder.rs
@@ -15,11 +15,9 @@
 // specific language governing permissions and limitations
 // under the License.
 
-use std::collections::HashMap;
-
 use bytes::Bytes;
 
-use crate::basic::Encoding;
+use crate::basic::{Encoding, EncodingMask};
 use crate::data_type::DataType;
 use crate::encodings::{
     decoding::{Decoder, DictDecoder, PlainDecoder, get_decoder},
@@ -68,9 +66,9 @@ pub trait RepetitionLevelDecoder: ColumnLevelDecoder {
 }
 
 pub trait DefinitionLevelDecoder: ColumnLevelDecoder {
-    /// Read up to `num_levels` definition levels into `out`
+    /// Read up to `num_levels` definition levels into `out`.
     ///
-    /// Returns the number of values skipped, and the number of levels skipped
+    /// Returns the number of values read, and the number of levels read.
     ///
     /// # Panics
     ///
@@ -81,9 +79,9 @@ pub trait DefinitionLevelDecoder: ColumnLevelDecoder {
         num_levels: usize,
     ) -> Result<(usize, usize)>;
 
-    /// Skips over `num_levels` definition levels
+    /// Skips over `num_levels` definition levels.
     ///
-    /// Returns the number of values skipped, and the number of levels skipped
+    /// Returns the number of values skipped, and the number of levels skipped.
     fn skip_def_levels(&mut self, num_levels: usize) -> Result<(usize, usize)>;
 }
 
@@ -136,14 +134,22 @@ 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 = Encoding::BYTE_STREAM_SPLIT as usize + 1;
+
 /// 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.
+    /// Uses `EncodingMask` and dense storage keyed by encoding discriminant.
+    decoder_mask: EncodingMask,
+    decoders: [Option<Box<dyn Decoder<T>>>; ENCODING_SLOTS],
 }
 
 impl<T: DataType> ColumnValueDecoder for ColumnValueDecoderImpl<T> {
@@ -153,7 +159,8 @@ impl<T: DataType> ColumnValueDecoder for ColumnValueDecoderImpl<T> {
         Self {
             descr: descr.clone(),
             current_encoding: None,
-            decoders: Default::default(),
+            decoder_mask: EncodingMask::default(),
+            decoders: std::array::from_fn(|_| None),
         }
     }
 
@@ -168,7 +175,7 @@ impl<T: DataType> ColumnValueDecoder for ColumnValueDecoderImpl<T> {
             encoding = Encoding::RLE_DICTIONARY
         }
 
-        if self.decoders.contains_key(&encoding) {
+        if self.decoder_mask.is_set(encoding) {
             return Err(general_err!("Column cannot have more than one dictionary"));
         }
 
@@ -178,7 +185,8 @@ impl<T: DataType> ColumnValueDecoder for ColumnValueDecoderImpl<T> {
 
             let mut decoder = DictDecoder::new();
             decoder.set_dict(Box::new(dictionary))?;
-            self.decoders.insert(encoding, Box::new(decoder));
+            self.decoders[encoding as usize] = Some(Box::new(decoder));
+            self.decoder_mask.insert(encoding);
             Ok(())
         } else {
             Err(nyi_err!(
@@ -195,25 +203,24 @@ impl<T: DataType> ColumnValueDecoder for ColumnValueDecoderImpl<T> {
         num_levels: usize,
         num_values: Option<usize>,
     ) -> Result<()> {
-        use std::collections::hash_map::Entry;
-
         if encoding == Encoding::PLAIN_DICTIONARY {
             encoding = Encoding::RLE_DICTIONARY;
         }
 
         let decoder = if encoding == Encoding::RLE_DICTIONARY {
-            self.decoders
-                .get_mut(&encoding)
+            self.decoders[encoding as usize]
+                .as_mut()
                 .expect("Decoder for dict should have been set")
         } else {
-            // Search cache for data page decoder
-            match self.decoders.entry(encoding) {
-                Entry::Occupied(e) => e.into_mut(),
-                Entry::Vacant(v) => {
-                    let data_decoder = get_decoder::<T>(self.descr.clone(), encoding)?;
-                    v.insert(data_decoder)
-                }
+            let slot = encoding as usize;
+            if self.decoders[slot].is_none() {
+                let data_decoder = get_decoder::<T>(self.descr.clone(), encoding)?;
+                self.decoders[slot] = Some(data_decoder);
+                self.decoder_mask.insert(encoding);
             }
+            self.decoders[slot]
+                .as_mut()
+                .expect("decoder should have been inserted")
         };
 
         decoder.set_data(data, num_values.unwrap_or(num_levels))?;
@@ -226,9 +233,8 @@ impl<T: DataType> ColumnValueDecoder for ColumnValueDecoderImpl<T> {
             .current_encoding
             .expect("current_encoding should be set");
 
-        let current_decoder = self
-            .decoders
-            .get_mut(&encoding)
+        let current_decoder = self.decoders[encoding as usize]
+            .as_mut()
             .unwrap_or_else(|| panic!("decoder for encoding {encoding} should be set"));
 
         // TODO: Push vec into decoder (#5177)
@@ -244,9 +250,8 @@ impl<T: DataType> ColumnValueDecoder for ColumnValueDecoderImpl<T> {
             .current_encoding
             .expect("current_encoding should be set");
 
-        let current_decoder = self
-            .decoders
-            .get_mut(&encoding)
+        let current_decoder = self.decoders[encoding as usize]
+            .as_mut()
             .unwrap_or_else(|| panic!("decoder for encoding {encoding} should be set"));
 
         current_decoder.skip(num_values)