limit vnode count to 2^15

Signed-off-by: Bugen Zhao <[email protected]>

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

@@ -68,7 +68,12 @@ impl VirtualNode {
 
 impl VirtualNode {
     /// The maximum count of virtual nodes that fits in [`VirtualNodeInner`].
-    pub const MAX_COUNT: usize = 1 << VirtualNodeInner::BITS;
+    ///
+    /// Note that the most significant bit is not used. This is because we use signed integers (`i16`)
+    /// for the scalar representation, where overflow can be confusing in terms of ordering.
+    // TODO(var-vnode): the only usage is in log-store, shall we update it by storing the vnode as
+    // bytea to enable 2^16 vnodes?
+    pub const MAX_COUNT: usize = 1 << (VirtualNodeInner::BITS - 1);
     /// The maximum value of the virtual node that can be represented.
     ///
     /// Note that this is **NOT** the maximum value of the virtual node, which depends on the configuration.
@@ -100,6 +105,7 @@ impl VirtualNode {
 
     /// Creates a virtual node from the given scalar representation. Used by `VNODE` expression.
     pub const fn from_scalar(scalar: i16) -> Self {
+        debug_assert!(scalar >= 0);
         Self(scalar as _)
     }
 
@@ -119,6 +125,7 @@ impl VirtualNode {
     /// Creates a virtual node from the given big-endian bytes representation.
     pub const fn from_be_bytes(bytes: [u8; Self::SIZE]) -> Self {
         let inner = VirtualNodeInner::from_be_bytes(bytes);
+        debug_assert!((inner as usize) < Self::MAX_COUNT);
         Self(inner)
     }