refactor: use u16 representation for virtual node (risingwavelabs#8385)

Signed-off-by: Bugen Zhao <i@bugenzhao.com>
Co-authored-by: Renjie Liu <liurenjie2008@gmail.com>

src/common/src/hash/consistent_hash/vnode.rs

@@ -20,14 +20,15 @@ use crate::hash::HashCode;
 // TODO: make it a newtype
 pub type ParallelUnitId = u32;
 
-/// `VirtualNode` (a.k.a. VNode) is a minimal partition that a set of keys belong to. It is used for
+/// `VirtualNode` (a.k.a. Vnode) is a minimal partition that a set of keys belong to. It is used for
 /// consistent hashing.
 #[repr(transparent)]
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord, Display)]
 #[display("{0}")]
 pub struct VirtualNode(VirtualNodeInner);
 
-type VirtualNodeInner = u8;
+/// The internal representation of a virtual node id.
+type VirtualNodeInner = u16;
 static_assertions::const_assert!(VirtualNodeInner::BITS >= VirtualNode::BITS as u32);
 
 impl From<HashCode> for VirtualNode {
@@ -41,6 +42,9 @@ impl From<HashCode> for VirtualNode {
 
 impl VirtualNode {
     /// The number of bits used to represent a virtual node.
+    ///
+    /// Note: Not all bits of the inner representation are used. One should rely on this constant
+    /// to determine the count of virtual nodes.
     pub const BITS: usize = 8;
     /// The total count of virtual nodes.
     pub const COUNT: usize = 1 << Self::BITS;

src/storage/hummock_sdk/src/filter_key_extractor.rs

@@ -359,6 +359,10 @@ mod tests {
     };
     use crate::key::TABLE_PREFIX_LEN;
 
+    const fn dummy_vnode() -> [u8; VirtualNode::SIZE] {
+        VirtualNode::from_index(233).to_be_bytes()
+    }
+
     #[test]
     fn test_default_filter_key_extractor() {
         let dummy_filter_key_extractor = DummyFilterKeyExtractor::default();
@@ -492,8 +496,7 @@ mod tests {
             buf.to_vec()
         };
 
-        let vnode_prefix = "v".as_bytes();
-        assert_eq!(VirtualNode::SIZE, vnode_prefix.len());
+        let vnode_prefix = &dummy_vnode()[..];
 
         let full_key = [&table_prefix, vnode_prefix, &row_bytes].concat();
         let output_key = schema_filter_key_extractor.extract(&full_key);
@@ -527,8 +530,7 @@ mod tests {
                 buf.to_vec()
             };
 
-            let vnode_prefix = "v".as_bytes();
-            assert_eq!(VirtualNode::SIZE, vnode_prefix.len());
+            let vnode_prefix = &dummy_vnode()[..];
 
             let full_key = [&table_prefix, vnode_prefix, &row_bytes].concat();
             let output_key = multi_filter_key_extractor.extract(&full_key);
@@ -565,8 +567,7 @@ mod tests {
                 buf.to_vec()
             };
 
-            let vnode_prefix = "v".as_bytes();
-            assert_eq!(VirtualNode::SIZE, vnode_prefix.len());
+            let vnode_prefix = &dummy_vnode()[..];
 
             let full_key = [&table_prefix, vnode_prefix, &row_bytes].concat();
             let output_key = multi_filter_key_extractor.extract(&full_key);