minor cleanup

libs/neonart/src/algorithm.rs

@@ -9,7 +9,6 @@ use crate::algorithm::node_ptr::MAX_PREFIX_LEN;
 use crate::algorithm::node_ref::{NewNodeRef, NodeRef, ReadLockedNodeRef, WriteLockedNodeRef};
 use crate::allocator::OutOfMemoryError;
 
-use crate::GarbageQueueFullError;
 use crate::TreeWriteGuard;
 use crate::UpdateAction;
 use crate::allocator::ArtAllocator;
@@ -21,7 +20,6 @@ pub(crate) type RootPtr<V> = node_ptr::NodePtr<V>;
 pub enum ArtError {
     ConcurrentUpdate, // need to retry
     OutOfMemory,
-    GarbageQueueFull,
 }
 
 impl From<ConcurrentUpdateError> for ArtError {
@@ -36,12 +34,6 @@ impl From<OutOfMemoryError> for ArtError {
     }
 }
 
-impl From<GarbageQueueFullError> for ArtError {
-    fn from(_: GarbageQueueFullError) -> ArtError {
-        ArtError::GarbageQueueFull
-    }
-}
-
 pub fn new_root<V: Value>(allocator: &impl ArtAllocator<V>) -> RootPtr<V> {
     node_ptr::new_root(allocator)
 }
@@ -114,11 +106,6 @@ pub(crate) fn update_fn<'e, 'g, K: Key, V: Value, A: ArtAllocator<V>, F>(
             Err(ArtError::OutOfMemory) => {
                 panic!("todo: OOM: try to GC, propagate to caller");
             }
-            Err(ArtError::GarbageQueueFull) => {
-                // FIXME: This can happen if someone is holding back the epoch. We should
-                // wait for the epoch to advance
-                panic!("todo: GC queue is full");
-            }
         }
     }
 }

libs/neonart/src/algorithm/lock_and_version.rs

@@ -1,3 +1,12 @@
+//! Each node in the tree has contains one atomic word that stores three things:
+//!
+//! Bit 0: set if the node is "obsolete". An obsolete node has been removed from the tree,
+//!        but might still be accessed by concurrent readers until the epoch expires.
+//! Bit 1: set if the node is currently write-locked. Used as a spinlock.
+//! Bits 2-63: Version number, incremented every time the node is modified.
+//!
+//! AtomicLockAndVersion represents that.
+
 use std::sync::atomic::{AtomicU64, Ordering};
 
 pub(crate) struct ConcurrentUpdateError();

libs/neonart/src/algorithm/node_ptr.rs

@@ -1,3 +1,6 @@
+//! This file contains the implementations of all the different node variants.
+//! These implementations use pointers, see node_ref.rs for slightly safer
+//! wrappers that deal with references instead.
 use std::marker::PhantomData;
 use std::ptr::NonNull;
 

libs/neonart/src/lib.rs

@@ -169,8 +169,6 @@ pub struct Tree<V: Value> {
 unsafe impl<V: Value + Sync> Sync for Tree<V> {}
 unsafe impl<V: Value + Send> Send for Tree<V> {}
 
-struct GarbageQueueFullError();
-
 struct GarbageQueue<V>(VecDeque<(NodePtr<V>, u64)>);
 
 unsafe impl<V: Value + Sync> Sync for GarbageQueue<V> {}

pgxn/neon/communicator/src/integrated_cache.rs

@@ -3,12 +3,12 @@
 //! It tracks:
 //! - Relation sizes and existence
 //! - Last-written LSN
-//! - TODO: Block cache (also known as LFC)
+//! - Block cache (also known as LFC)
 //!
 //! TODO: limit the size
 //! TODO: concurrency
 //!
-//! Note: This deals with "relations", which is really just one "relation fork" in Postgres
+//! Note: This deals with "relations" which is really just one "relation fork" in Postgres
 //! terms. RelFileLocator + ForkNumber is the key.
 
 //