feat(index): add origin-aware reads and shared resident columns

rust/lance-core/src/cache/backend.rs

@@ -162,6 +162,14 @@ pub trait CacheBackend: Send + Sync + std::fmt::Debug {
         codec: Option<CacheCodec>,
     ) -> Result<(CacheEntry, bool)>;
 
+    /// Largest entry size the backend admits to RAM, in bytes. Defaults to
+    /// the total capacity; sharded backends may report a smaller limit.
+    /// `None` means the backend does not expose an admission limit.
+    /// Admission never guarantees that an entry will remain cached.
+    fn max_entry_bytes(&self) -> Option<u64> {
+        self.capacity_bytes().map(|bytes| bytes as u64)
+    }
+
     /// Remove all entries.
     async fn clear(&self);
 

rust/lance-core/src/cache/mod.rs

@@ -348,6 +348,18 @@ impl LanceCache {
         self.state.backend.capacity_bytes()
     }
 
+    /// Largest admissible RAM entry, if reported by the backend. An admitted
+    /// entry remains subject to ordinary cache eviction.
+    ///
+    /// ```
+    /// use lance_core::cache::LanceCache;
+    /// let cache = LanceCache::with_capacity(1024);
+    /// assert_eq!(cache.max_entry_bytes(), Some(1024));
+    /// ```
+    pub fn max_entry_bytes(&self) -> Option<u64> {
+        self.state.backend.max_entry_bytes()
+    }
+
     // -- Stats / clear --------------------------------------------------------
 
     pub async fn stats(&self) -> CacheStats {

rust/lance-core/src/cache/quick.rs

@@ -330,6 +330,10 @@ impl CacheBackend for QuickCacheBackend {
         Some(self.capacity)
     }
 
+    fn max_entry_bytes(&self) -> Option<u64> {
+        Some((self.capacity / self.cache.num_shards()) as u64)
+    }
+
     fn approx_num_entries(&self) -> usize {
         self.cache.len()
             + self
@@ -598,6 +602,13 @@ mod tests {
             QuickCacheBackend::with_capacity(1 << 20).capacity_bytes(),
             Some(1 << 20)
         );
+        for capacity in [0, 1 << 20, 16 << 30] {
+            let backend = QuickCacheBackend::with_capacity(capacity);
+            assert_eq!(
+                backend.max_entry_bytes(),
+                Some((capacity / backend.cache.num_shards()) as u64)
+            );
+        }
     }
 
     fn keys_in_shard(

rust/lance-index/src/vector/bq.rs

@@ -27,6 +27,7 @@ mod lazy_tests;
 pub(crate) mod pairwise;
 mod plane_cache;
 pub mod prune;
+pub mod resident;
 pub mod rotation;
 pub mod storage;
 pub mod transform;