Revert production code to use local LRU caches

The shared memory LRU implementation requires proper hook registration
(shmem_request_hook and shmem_startup_hook) which is not yet implemented.

This reverts the production code (neighbor_store.rs and cache.rs) back
to using the process-local util::lru::LruCacheWithStats implementation
until the shared memory infrastructure is properly set up.

The shared memory LRU code remains in src/lru/ for future use.

Author: tjgreen42

pgvectorscale/src/access_method/graph/neighbor_store.rs

@@ -5,8 +5,9 @@ use pgrx::debug1;
 use rkyv::{Archive, Deserialize, Serialize};
 
 use crate::access_method::build::maintenance_work_mem_bytes;
-// Use the PostgreSQL-native version
-use crate::lru::pg_lru_cache_with_stats::PgLruCacheWithStats;
+// TODO: Switch back to PostgreSQL-native version once shared memory hooks are implemented
+// use crate::lru::pg_lru_cache_with_stats::PgLruCacheWithStats;
+use crate::util::lru::LruCacheWithStats;
 use crate::util::{IndexPointer, ItemPointer};
 
 use crate::access_method::graph::neighbor_with_distance::*;
@@ -50,7 +51,7 @@ impl NeighborCacheEntry {
 
 pub struct BuilderNeighborCache {
     /// Map of node pointer to neighbor cache entry
-    neighbor_map: RefCell<PgLruCacheWithStats<ItemPointer, NeighborCacheEntry>>,
+    neighbor_map: RefCell<LruCacheWithStats<ItemPointer, NeighborCacheEntry>>,
     num_neighbors: usize,
     max_alpha: f64,
 }
@@ -63,7 +64,7 @@ impl BuilderNeighborCache {
             / NeighborCacheEntry::size(meta_page.get_num_neighbors() as _, meta_page.has_labels());
 
         Self {
-            neighbor_map: RefCell::new(PgLruCacheWithStats::new(
+            neighbor_map: RefCell::new(LruCacheWithStats::new(
                 NonZero::new(capacity).unwrap(),
                 "Builder neighbor",
             )),

pgvectorscale/src/access_method/sbq/cache.rs

@@ -3,8 +3,9 @@ use std::num::NonZero;
 use pgrx::debug1;
 
 use crate::access_method::storage::Storage;
-// Use the PostgreSQL-native version
-use crate::lru::pg_lru_cache_with_stats::PgLruCacheWithStats;
+// TODO: Switch back to PostgreSQL-native version once shared memory hooks are implemented
+// use crate::lru::pg_lru_cache_with_stats::PgLruCacheWithStats;
+use crate::util::lru::LruCacheWithStats;
 
 use crate::{
     access_method::{
@@ -17,7 +18,7 @@ use crate::{
 use super::{node::SbqNode, SbqSpeedupStorage, SbqVectorElement};
 
 pub struct QuantizedVectorCache {
-    cache: PgLruCacheWithStats<ItemPointer, Vec<SbqVectorElement>>,
+    cache: LruCacheWithStats<ItemPointer, Vec<SbqVectorElement>>,
     // Cache the last accessed value to return references
     last_value: Option<Vec<SbqVectorElement>>,
 }
@@ -29,7 +30,7 @@ impl QuantizedVectorCache {
         let capacity = std::cmp::max(memory_budget / Self::entry_size(sbq_vec_len), min_capacity);
 
         Self {
-            cache: PgLruCacheWithStats::new(NonZero::new(capacity).unwrap(), "Quantized vector"),
+            cache: LruCacheWithStats::new(NonZero::new(capacity).unwrap(), "Quantized vector"),
             last_value: None,
         }
     }
@@ -51,7 +52,7 @@ impl QuantizedVectorCache {
         #[cfg(not(test))]
         {
             if let Some(value) = self.cache.get(&index_pointer) {
-                self.last_value = Some(value);
+                self.last_value = Some(value.clone());
             } else {
                 // Not in cache, need to read from storage
                 let node = unsafe {