Implement table gc, currently for block_ref and version only

src/table/data.rs

@@ -1,3 +1,4 @@
+use core::borrow::Borrow;
 use std::sync::Arc;
 
 use log::warn;
@@ -17,6 +18,7 @@ pub struct TableData<F: TableSchema> {
 	pub instance: F,
 
 	pub store: sled::Tree,
+	pub gc_todo: sled::Tree,
 	pub merkle_updater: Arc<MerkleUpdater>,
 }
 
@@ -41,6 +43,10 @@ where
 			.open_tree(&format!("{}:merkle_tree", name))
 			.expect("Unable to open DB Merkle tree tree");
 
+		let gc_todo = db
+			.open_tree(&format!("{}:gc_todo", name))
+			.expect("Unable to open DB tree");
+
 		let merkle_updater = MerkleUpdater::launch(
 			name.clone(),
 			background,
@@ -52,6 +58,7 @@ where
 			name,
 			instance,
 			store,
+			gc_todo,
 			merkle_updater,
 		})
 	}
@@ -103,10 +110,17 @@ where
 	}
 
 	// Mutation functions
+	// When changing this code, take care of propagating modifications correctly:
+	// - When an entry is modified or deleted, call the updated() function
+	//   on the table instance
+	// - When an entry is modified or deleted, add it to the merkle updater's todo list.
+	//   This has to be done atomically with the modification for the merkle updater
+	//   to maintain consistency. The merkle updater must then be notified with todo_notify.
+	// - When an entry is updated to be a tombstone, add it to the gc_todo tree
 
-	pub(crate) fn update_many(&self, entries: &[Arc<ByteBuf>]) -> Result<(), Error> {
+	pub(crate) fn update_many<T: Borrow<ByteBuf>>(&self, entries: &[T]) -> Result<(), Error> {
 		for update_bytes in entries.iter() {
-			self.update_entry(update_bytes.as_slice())?;
+			self.update_entry(update_bytes.borrow().as_slice())?;
 		}
 		Ok(())
 	}
@@ -115,8 +129,8 @@ where
 		let update = self.decode_entry(update_bytes)?;
 		let tree_key = self.tree_key(update.partition_key(), update.sort_key());
 
-		let changed = (&self.store, &self.merkle_updater.todo).transaction(|(db, mkl_todo)| {
-			let (old_entry, new_entry) = match db.get(&tree_key)? {
+		let changed = (&self.store, &self.merkle_updater.todo).transaction(|(store, mkl_todo)| {
+			let (old_entry, new_entry) = match store.get(&tree_key)? {
 				Some(prev_bytes) => {
 					let old_entry = self
 						.decode_entry(&prev_bytes)
@@ -132,27 +146,32 @@ where
 				let new_bytes = rmp_to_vec_all_named(&new_entry)
 					.map_err(Error::RMPEncode)
 					.map_err(sled::transaction::ConflictableTransactionError::Abort)?;
-				mkl_todo.insert(tree_key.clone(), blake2sum(&new_bytes[..]).to_vec())?;
-				db.insert(tree_key.clone(), new_bytes)?;
-				Ok(Some((old_entry, new_entry)))
+				let new_bytes_hash = blake2sum(&new_bytes[..]);
+				mkl_todo.insert(tree_key.clone(), new_bytes_hash.as_slice())?;
+				store.insert(tree_key.clone(), new_bytes)?;
+				Ok(Some((old_entry, new_entry, new_bytes_hash)))
 			} else {
 				Ok(None)
 			}
 		})?;
 
-		if let Some((old_entry, new_entry)) = changed {
+		if let Some((old_entry, new_entry, new_bytes_hash)) = changed {
+			let is_tombstone = new_entry.is_tombstone();
 			self.instance.updated(old_entry, Some(new_entry));
 			self.merkle_updater.todo_notify.notify();
+			if is_tombstone {
+				self.gc_todo.insert(&tree_key, new_bytes_hash.as_slice())?;
+			}
 		}
 
 		Ok(())
 	}
 
 	pub(crate) fn delete_if_equal(self: &Arc<Self>, k: &[u8], v: &[u8]) -> Result<bool, Error> {
-		let removed = (&self.store, &self.merkle_updater.todo).transaction(|(txn, mkl_todo)| {
-			if let Some(cur_v) = txn.get(k)? {
+		let removed = (&self.store, &self.merkle_updater.todo).transaction(|(store, mkl_todo)| {
+			if let Some(cur_v) = store.get(k)? {
 				if cur_v == v {
-					txn.remove(k)?;
+					store.remove(k)?;
 					mkl_todo.insert(k, vec![])?;
 					return Ok(true);
 				}
@@ -168,6 +187,30 @@ where
 		Ok(removed)
 	}
 
+	pub(crate) fn delete_if_equal_hash(self: &Arc<Self>, k: &[u8], vhash: Hash) -> Result<bool, Error> {
+		let removed = (&self.store, &self.merkle_updater.todo).transaction(|(store, mkl_todo)| {
+			if let Some(cur_v) = store.get(k)? {
+				if blake2sum(&cur_v[..]) == vhash {
+					store.remove(k)?;
+					mkl_todo.insert(k, vec![])?;
+					return Ok(Some(cur_v));
+				}
+			}
+			Ok(None)
+		})?;
+
+		if let Some(old_v) = removed {
+			let old_entry = self.decode_entry(&old_v[..])?;
+			self.instance.updated(Some(old_entry), None);
+			self.merkle_updater.todo_notify.notify();
+			Ok(true)
+		} else {
+			Ok(false)
+		}
+	}
+
+	// ---- Utility functions ----
+
 	pub(crate) fn tree_key(&self, p: &F::P, s: &F::S) -> Vec<u8> {
 		let mut ret = p.hash().to_vec();
 		ret.extend(s.sort_key());