Merge pull request 'Remove Sled' (#767) from rm-sled into next-0.10

Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/767

8 files changed, 265 insertions, 518 deletions

diff --git a/src/db/Cargo.toml b/src/db/Cargo.toml
index fddc5cca..a8f6d586 100644
--- a/src/db/Cargo.toml
+++ b/src/db/Cargo.toml
@@ -18,13 +18,12 @@ tracing.workspace = true
 
 heed = { workspace = true, optional = true }
 rusqlite = { workspace = true, optional = true }
-sled = { workspace = true, optional = true }
 
 [dev-dependencies]
 mktemp.workspace = true
 
 [features]
-default = [ "sled", "lmdb", "sqlite" ]
+default = [ "lmdb", "sqlite" ]
 bundled-libs = [ "rusqlite?/bundled" ]
 lmdb = [ "heed" ]
 sqlite = [ "rusqlite" ]
diff --git a/src/db/counted_tree_hack.rs b/src/db/counted_tree_hack.rs
deleted file mode 100644
index a4ce12e0..00000000
--- a/src/db/counted_tree_hack.rs
+++ /dev/null
@@ -1,127 +0,0 @@
-//! This hack allows a db tree to keep in RAM a counter of the number of entries
-//! it contains, which is used to call .len() on it.  This is usefull only for
-//! the sled backend where .len() otherwise would have to traverse the whole
-//! tree to count items.  For sqlite and lmdb, this is mostly useless (but
-//! hopefully not harmfull!). Note that a CountedTree cannot be part of a
-//! transaction.
-
-use std::sync::{
-	atomic::{AtomicUsize, Ordering},
-	Arc,
-};
-
-use crate::{Result, Tree, TxError, Value, ValueIter};
-
-#[derive(Clone)]
-pub struct CountedTree(Arc<CountedTreeInternal>);
-
-struct CountedTreeInternal {
-	tree: Tree,
-	len: AtomicUsize,
-}
-
-impl CountedTree {
-	pub fn new(tree: Tree) -> Result<Self> {
-		let len = tree.len()?;
-		Ok(Self(Arc::new(CountedTreeInternal {
-			tree,
-			len: AtomicUsize::new(len),
-		})))
-	}
-
-	pub fn len(&self) -> usize {
-		self.0.len.load(Ordering::SeqCst)
-	}
-
-	pub fn is_empty(&self) -> bool {
-		self.len() == 0
-	}
-
-	pub fn get<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<Value>> {
-		self.0.tree.get(key)
-	}
-
-	pub fn first(&self) -> Result<Option<(Value, Value)>> {
-		self.0.tree.first()
-	}
-
-	pub fn iter(&self) -> Result<ValueIter<'_>> {
-		self.0.tree.iter()
-	}
-
-	// ---- writing functions ----
-
-	pub fn insert<K, V>(&self, key: K, value: V) -> Result<Option<Value>>
-	where
-		K: AsRef<[u8]>,
-		V: AsRef<[u8]>,
-	{
-		let old_val = self.0.tree.insert(key, value)?;
-		if old_val.is_none() {
-			self.0.len.fetch_add(1, Ordering::SeqCst);
-		}
-		Ok(old_val)
-	}
-
-	pub fn remove<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<Value>> {
-		let old_val = self.0.tree.remove(key)?;
-		if old_val.is_some() {
-			self.0.len.fetch_sub(1, Ordering::SeqCst);
-		}
-		Ok(old_val)
-	}
-
-	pub fn compare_and_swap<K, OV, NV>(
-		&self,
-		key: K,
-		expected_old: Option<OV>,
-		new: Option<NV>,
-	) -> Result<bool>
-	where
-		K: AsRef<[u8]>,
-		OV: AsRef<[u8]>,
-		NV: AsRef<[u8]>,
-	{
-		let old_some = expected_old.is_some();
-		let new_some = new.is_some();
-
-		let tx_res = self.0.tree.db().transaction(|tx| {
-			let old_val = tx.get(&self.0.tree, &key)?;
-			let is_same = match (&old_val, &expected_old) {
-				(None, None) => true,
-				(Some(x), Some(y)) if x == y.as_ref() => true,
-				_ => false,
-			};
-			if is_same {
-				match &new {
-					Some(v) => {
-						tx.insert(&self.0.tree, &key, v)?;
-					}
-					None => {
-						tx.remove(&self.0.tree, &key)?;
-					}
-				}
-				Ok(())
-			} else {
-				Err(TxError::Abort(()))
-			}
-		});
-
-		match tx_res {
-			Ok(()) => {
-				match (old_some, new_some) {
-					(false, true) => {
-						self.0.len.fetch_add(1, Ordering::SeqCst);
-					}
-					(true, false) => {
-						self.0.len.fetch_sub(1, Ordering::SeqCst);
-					}
-					_ => (),
-				}
-				Ok(true)
-			}
-			Err(TxError::Abort(())) => Ok(false),
-			Err(TxError::Db(e)) => Err(e),
-		}
-	}
-}
diff --git a/src/db/lib.rs b/src/db/lib.rs
index 0fb457ce..ff511b5f 100644
--- a/src/db/lib.rs
+++ b/src/db/lib.rs
@@ -3,13 +3,9 @@ extern crate tracing;
 
 #[cfg(feature = "lmdb")]
 pub mod lmdb_adapter;
-#[cfg(feature = "sled")]
-pub mod sled_adapter;
 #[cfg(feature = "sqlite")]
 pub mod sqlite_adapter;
 
-pub mod counted_tree_hack;
-
 pub mod open;
 
 #[cfg(test)]
@@ -55,6 +51,7 @@ pub type Result<T> = std::result::Result<T, Error>;
 pub struct TxOpError(pub(crate) Error);
 pub type TxOpResult<T> = std::result::Result<T, TxOpError>;
 
+#[derive(Debug)]
 pub enum TxError<E> {
 	Abort(E),
 	Db(Error),
@@ -189,10 +186,6 @@ impl Tree {
 	pub fn len(&self) -> Result<usize> {
 		self.0.len(self.1)
 	}
-	#[inline]
-	pub fn fast_len(&self) -> Result<Option<usize>> {
-		self.0.fast_len(self.1)
-	}
 
 	#[inline]
 	pub fn first(&self) -> Result<Option<(Value, Value)>> {
@@ -282,6 +275,11 @@ impl<'a> Transaction<'a> {
 	pub fn remove<T: AsRef<[u8]>>(&mut self, tree: &Tree, key: T) -> TxOpResult<Option<Value>> {
 		self.tx.remove(tree.1, key.as_ref())
 	}
+	/// Clears all values in a tree
+	#[inline]
+	pub fn clear(&mut self, tree: &Tree) -> TxOpResult<()> {
+		self.tx.clear(tree.1)
+	}
 
 	#[inline]
 	pub fn iter(&self, tree: &Tree) -> TxOpResult<TxValueIter<'_>> {
@@ -328,9 +326,6 @@ pub(crate) trait IDb: Send + Sync {
 
 	fn get(&self, tree: usize, key: &[u8]) -> Result<Option<Value>>;
 	fn len(&self, tree: usize) -> Result<usize>;
-	fn fast_len(&self, _tree: usize) -> Result<Option<usize>> {
-		Ok(None)
-	}
 
 	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<Option<Value>>;
 	fn remove(&self, tree: usize, key: &[u8]) -> Result<Option<Value>>;
@@ -361,6 +356,7 @@ pub(crate) trait ITx {
 
 	fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> TxOpResult<Option<Value>>;
 	fn remove(&mut self, tree: usize, key: &[u8]) -> TxOpResult<Option<Value>>;
+	fn clear(&mut self, tree: usize) -> TxOpResult<()>;
 
 	fn iter(&self, tree: usize) -> TxOpResult<TxValueIter<'_>>;
 	fn iter_rev(&self, tree: usize) -> TxOpResult<TxValueIter<'_>>;
diff --git a/src/db/lmdb_adapter.rs b/src/db/lmdb_adapter.rs
index 59fa132d..5ce7d3e3 100644
--- a/src/db/lmdb_adapter.rs
+++ b/src/db/lmdb_adapter.rs
@@ -3,6 +3,7 @@ use core::ptr::NonNull;
 
 use std::collections::HashMap;
 use std::convert::TryInto;
+use std::pin::Pin;
 use std::sync::{Arc, RwLock};
 
 use heed::types::ByteSlice;
@@ -121,10 +122,6 @@ impl IDb for LmdbDb {
 		Ok(tree.len(&tx)?.try_into().unwrap())
 	}
 
-	fn fast_len(&self, tree: usize) -> Result<Option<usize>> {
-		Ok(Some(self.len(tree)?))
-	}
-
 	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<Option<Value>> {
 		let tree = self.get_tree(tree)?;
 		let mut tx = self.db.write_txn()?;
@@ -242,8 +239,9 @@ impl<'a> ITx for LmdbTx<'a> {
 			None => Ok(None),
 		}
 	}
-	fn len(&self, _tree: usize) -> TxOpResult<usize> {
-		unimplemented!(".len() in transaction not supported with LMDB backend")
+	fn len(&self, tree: usize) -> TxOpResult<usize> {
+		let tree = self.get_tree(tree)?;
+		Ok(tree.len(&self.tx)? as usize)
 	}
 
 	fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> TxOpResult<Option<Value>> {
@@ -258,33 +256,48 @@ impl<'a> ITx for LmdbTx<'a> {
 		tree.delete(&mut self.tx, key)?;
 		Ok(old_val)
 	}
+	fn clear(&mut self, tree: usize) -> TxOpResult<()> {
+		let tree = *self.get_tree(tree)?;
+		tree.clear(&mut self.tx)?;
+		Ok(())
+	}
 
-	fn iter(&self, _tree: usize) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!("Iterators in transactions not supported with LMDB backend");
+	fn iter(&self, tree: usize) -> TxOpResult<TxValueIter<'_>> {
+		let tree = *self.get_tree(tree)?;
+		Ok(Box::new(tree.iter(&self.tx)?.map(tx_iter_item)))
 	}
-	fn iter_rev(&self, _tree: usize) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!("Iterators in transactions not supported with LMDB backend");
+	fn iter_rev(&self, tree: usize) -> TxOpResult<TxValueIter<'_>> {
+		let tree = *self.get_tree(tree)?;
+		Ok(Box::new(tree.rev_iter(&self.tx)?.map(tx_iter_item)))
 	}
 
 	fn range<'r>(
 		&self,
-		_tree: usize,
-		_low: Bound<&'r [u8]>,
-		_high: Bound<&'r [u8]>,
+		tree: usize,
+		low: Bound<&'r [u8]>,
+		high: Bound<&'r [u8]>,
 	) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!("Iterators in transactions not supported with LMDB backend");
+		let tree = *self.get_tree(tree)?;
+		Ok(Box::new(
+			tree.range(&self.tx, &(low, high))?.map(tx_iter_item),
+		))
 	}
 	fn range_rev<'r>(
 		&self,
-		_tree: usize,
-		_low: Bound<&'r [u8]>,
-		_high: Bound<&'r [u8]>,
+		tree: usize,
+		low: Bound<&'r [u8]>,
+		high: Bound<&'r [u8]>,
 	) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!("Iterators in transactions not supported with LMDB backend");
+		let tree = *self.get_tree(tree)?;
+		Ok(Box::new(
+			tree.rev_range(&self.tx, &(low, high))?.map(tx_iter_item),
+		))
 	}
 }
 
-// ----
+// ---- iterators outside transactions ----
+// complicated, they must hold the transaction object
+// therefore a bit of unsafe code (it is a self-referential struct)
 
 type IteratorItem<'a> = heed::Result<(
 	<ByteSlice as BytesDecode<'a>>::DItem,
@@ -307,12 +320,20 @@ where
 	where
 		F: FnOnce(&'a RoTxn<'a>) -> Result<I>,
 	{
-		let mut res = TxAndIterator { tx, iter: None };
+		let res = TxAndIterator { tx, iter: None };
+		let mut boxed = Box::pin(res);
+
+		// This unsafe allows us to bypass lifetime checks
+		let tx = unsafe { NonNull::from(&boxed.tx).as_ref() };
+		let iter = iterfun(tx)?;
 
-		let tx = unsafe { NonNull::from(&res.tx).as_ref() };
-		res.iter = Some(iterfun(tx)?);
+		let mut_ref = Pin::as_mut(&mut boxed);
+		// This unsafe allows us to write in a field of the pinned struct
+		unsafe {
+			Pin::get_unchecked_mut(mut_ref).iter = Some(iter);
+		}
 
-		Ok(Box::new(res))
+		Ok(Box::new(TxAndIteratorPin(boxed)))
 	}
 }
 
@@ -321,18 +342,26 @@ where
 	I: Iterator<Item = IteratorItem<'a>> + 'a,
 {
 	fn drop(&mut self) {
+		// ensure the iterator is dropped before the RoTxn it references
 		drop(self.iter.take());
 	}
 }
 
-impl<'a, I> Iterator for TxAndIterator<'a, I>
+struct TxAndIteratorPin<'a, I>(Pin<Box<TxAndIterator<'a, I>>>)
+where
+	I: Iterator<Item = IteratorItem<'a>> + 'a;
+
+impl<'a, I> Iterator for TxAndIteratorPin<'a, I>
 where
 	I: Iterator<Item = IteratorItem<'a>> + 'a,
 {
 	type Item = Result<(Value, Value)>;
 
 	fn next(&mut self) -> Option<Self::Item> {
-		match self.iter.as_mut().unwrap().next() {
+		let mut_ref = Pin::as_mut(&mut self.0);
+		// This unsafe allows us to mutably access the iterator field
+		let next = unsafe { Pin::get_unchecked_mut(mut_ref).iter.as_mut()?.next() };
+		match next {
 			None => None,
 			Some(Err(e)) => Some(Err(e.into())),
 			Some(Ok((k, v))) => Some(Ok((k.to_vec(), v.to_vec()))),
@@ -340,7 +369,16 @@ where
 	}
 }
 
-// ----
+// ---- iterators within transactions ----
+
+fn tx_iter_item<'a>(
+	item: std::result::Result<(&'a [u8], &'a [u8]), heed::Error>,
+) -> TxOpResult<(Vec<u8>, Vec<u8>)> {
+	item.map(|(k, v)| (k.to_vec(), v.to_vec()))
+		.map_err(|e| TxOpError(Error::from(e)))
+}
+
+// ---- utility ----
 
 #[cfg(target_pointer_width = "64")]
 pub fn recommended_map_size() -> usize {
diff --git a/src/db/open.rs b/src/db/open.rs
index ae135c4e..03476a42 100644
--- a/src/db/open.rs
+++ b/src/db/open.rs
@@ -11,7 +11,6 @@ use crate::{Db, Error, Result};
 pub enum Engine {
 	Lmdb,
 	Sqlite,
-	Sled,
 }
 
 impl Engine {
@@ -20,7 +19,6 @@ impl Engine {
 		match self {
 			Self::Lmdb => "lmdb",
 			Self::Sqlite => "sqlite",
-			Self::Sled => "sled",
 		}
 	}
 }
@@ -38,10 +36,10 @@ impl std::str::FromStr for Engine {
 		match text {
 			"lmdb" | "heed" => Ok(Self::Lmdb),
 			"sqlite" | "sqlite3" | "rusqlite" => Ok(Self::Sqlite),
-			"sled" => Ok(Self::Sled),
+			"sled" => Err(Error("Sled is no longer supported as a database engine. Converting your old metadata db can be done using an older Garage binary (e.g. v0.9.3).".into())),
 			kind => Err(Error(
 				format!(
-					"Invalid DB engine: {} (options are: lmdb, sled, sqlite)",
+					"Invalid DB engine: {} (options are: lmdb, sqlite)",
 					kind
 				)
 				.into(),
@@ -53,8 +51,6 @@ impl std::str::FromStr for Engine {
 pub struct OpenOpt {
 	pub fsync: bool,
 	pub lmdb_map_size: Option<usize>,
-	pub sled_cache_capacity: usize,
-	pub sled_flush_every_ms: u64,
 }
 
 impl Default for OpenOpt {
@@ -62,31 +58,12 @@ impl Default for OpenOpt {
 		Self {
 			fsync: false,
 			lmdb_map_size: None,
-			sled_cache_capacity: 1024 * 1024 * 1024,
-			sled_flush_every_ms: 2000,
 		}
 	}
 }
 
 pub fn open_db(path: &PathBuf, engine: Engine, opt: &OpenOpt) -> Result<Db> {
 	match engine {
-		// ---- Sled DB ----
-		#[cfg(feature = "sled")]
-		Engine::Sled => {
-			if opt.fsync {
-				return Err(Error(
-					"`metadata_fsync = true` is not supported with the Sled database engine".into(),
-				));
-			}
-			info!("Opening Sled database at: {}", path.display());
-			let db = crate::sled_adapter::sled::Config::default()
-				.path(&path)
-				.cache_capacity(opt.sled_cache_capacity as u64)
-				.flush_every_ms(Some(opt.sled_flush_every_ms))
-				.open()?;
-			Ok(crate::sled_adapter::SledDb::init(db))
-		}
-
 		// ---- Sqlite DB ----
 		#[cfg(feature = "sqlite")]
 		Engine::Sqlite => {
diff --git a/src/db/sled_adapter.rs b/src/db/sled_adapter.rs
deleted file mode 100644
index 84f2001b..00000000
--- a/src/db/sled_adapter.rs
+++ /dev/null
@@ -1,274 +0,0 @@
-use core::ops::Bound;
-
-use std::cell::Cell;
-use std::collections::HashMap;
-use std::sync::{Arc, RwLock};
-
-use sled::transaction::{
-	ConflictableTransactionError, TransactionError, Transactional, TransactionalTree,
-	UnabortableTransactionError,
-};
-
-use crate::{
-	Db, Error, IDb, ITx, ITxFn, OnCommit, Result, TxError, TxFnResult, TxOpError, TxOpResult,
-	TxResult, TxValueIter, Value, ValueIter,
-};
-
-pub use sled;
-
-// -- err
-
-impl From<sled::Error> for Error {
-	fn from(e: sled::Error) -> Error {
-		Error(format!("Sled: {}", e).into())
-	}
-}
-
-impl From<sled::Error> for TxOpError {
-	fn from(e: sled::Error) -> TxOpError {
-		TxOpError(e.into())
-	}
-}
-
-// -- db
-
-pub struct SledDb {
-	db: sled::Db,
-	trees: RwLock<(Vec<sled::Tree>, HashMap<String, usize>)>,
-}
-
-impl SledDb {
-	#[deprecated(
-		since = "0.9.0",
-		note = "The Sled database is now deprecated and will be removed in Garage v1.0. Please migrate to LMDB or Sqlite as soon as possible."
-	)]
-	pub fn init(db: sled::Db) -> Db {
-		tracing::warn!("--------------------    IMPORTANT WARNING !!!    ----------------------");
-		tracing::warn!("The Sled database is now deprecated and will be removed in Garage v1.0.");
-		tracing::warn!("Please migrate to LMDB or Sqlite as soon as possible.");
-		tracing::warn!("-----------------------------------------------------------------------");
-		let s = Self {
-			db,
-			trees: RwLock::new((Vec::new(), HashMap::new())),
-		};
-		Db(Arc::new(s))
-	}
-
-	fn get_tree(&self, i: usize) -> Result<sled::Tree> {
-		self.trees
-			.read()
-			.unwrap()
-			.0
-			.get(i)
-			.cloned()
-			.ok_or_else(|| Error("invalid tree id".into()))
-	}
-}
-
-impl IDb for SledDb {
-	fn engine(&self) -> String {
-		"Sled".into()
-	}
-
-	fn open_tree(&self, name: &str) -> Result<usize> {
-		let mut trees = self.trees.write().unwrap();
-		if let Some(i) = trees.1.get(name) {
-			Ok(*i)
-		} else {
-			let tree = self.db.open_tree(name)?;
-			let i = trees.0.len();
-			trees.0.push(tree);
-			trees.1.insert(name.to_string(), i);
-			Ok(i)
-		}
-	}
-
-	fn list_trees(&self) -> Result<Vec<String>> {
-		let mut trees = vec![];
-		for name in self.db.tree_names() {
-			let name = std::str::from_utf8(&name)
-				.map_err(|e| Error(format!("{}", e).into()))?
-				.to_string();
-			if name != "__sled__default" {
-				trees.push(name);
-			}
-		}
-		Ok(trees)
-	}
-
-	// ----
-
-	fn get(&self, tree: usize, key: &[u8]) -> Result<Option<Value>> {
-		let tree = self.get_tree(tree)?;
-		let val = tree.get(key)?;
-		Ok(val.map(|x| x.to_vec()))
-	}
-
-	fn len(&self, tree: usize) -> Result<usize> {
-		let tree = self.get_tree(tree)?;
-		Ok(tree.len())
-	}
-
-	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<Option<Value>> {
-		let tree = self.get_tree(tree)?;
-		let old_val = tree.insert(key, value)?;
-		Ok(old_val.map(|x| x.to_vec()))
-	}
-
-	fn remove(&self, tree: usize, key: &[u8]) -> Result<Option<Value>> {
-		let tree = self.get_tree(tree)?;
-		let old_val = tree.remove(key)?;
-		Ok(old_val.map(|x| x.to_vec()))
-	}
-
-	fn clear(&self, tree: usize) -> Result<()> {
-		let tree = self.get_tree(tree)?;
-		tree.clear()?;
-		Ok(())
-	}
-
-	fn iter(&self, tree: usize) -> Result<ValueIter<'_>> {
-		let tree = self.get_tree(tree)?;
-		Ok(Box::new(tree.iter().map(|v| {
-			v.map(|(x, y)| (x.to_vec(), y.to_vec())).map_err(Into::into)
-		})))
-	}
-
-	fn iter_rev(&self, tree: usize) -> Result<ValueIter<'_>> {
-		let tree = self.get_tree(tree)?;
-		Ok(Box::new(tree.iter().rev().map(|v| {
-			v.map(|(x, y)| (x.to_vec(), y.to_vec())).map_err(Into::into)
-		})))
-	}
-
-	fn range<'r>(
-		&self,
-		tree: usize,
-		low: Bound<&'r [u8]>,
-		high: Bound<&'r [u8]>,
-	) -> Result<ValueIter<'_>> {
-		let tree = self.get_tree(tree)?;
-		Ok(Box::new(tree.range::<&'r [u8], _>((low, high)).map(|v| {
-			v.map(|(x, y)| (x.to_vec(), y.to_vec())).map_err(Into::into)
-		})))
-	}
-	fn range_rev<'r>(
-		&self,
-		tree: usize,
-		low: Bound<&'r [u8]>,
-		high: Bound<&'r [u8]>,
-	) -> Result<ValueIter<'_>> {
-		let tree = self.get_tree(tree)?;
-		Ok(Box::new(tree.range::<&'r [u8], _>((low, high)).rev().map(
-			|v| v.map(|(x, y)| (x.to_vec(), y.to_vec())).map_err(Into::into),
-		)))
-	}
-
-	// ----
-
-	fn transaction(&self, f: &dyn ITxFn) -> TxResult<OnCommit, ()> {
-		let trees = self.trees.read().unwrap();
-		let res = trees.0.transaction(|txtrees| {
-			let mut tx = SledTx {
-				trees: txtrees,
-				err: Cell::new(None),
-			};
-			match f.try_on(&mut tx) {
-				TxFnResult::Ok(on_commit) => {
-					assert!(tx.err.into_inner().is_none());
-					Ok(on_commit)
-				}
-				TxFnResult::Abort => {
-					assert!(tx.err.into_inner().is_none());
-					Err(ConflictableTransactionError::Abort(()))
-				}
-				TxFnResult::DbErr => {
-					let e = tx.err.into_inner().expect("No DB error");
-					Err(e.into())
-				}
-			}
-		});
-		match res {
-			Ok(on_commit) => Ok(on_commit),
-			Err(TransactionError::Abort(())) => Err(TxError::Abort(())),
-			Err(TransactionError::Storage(s)) => Err(TxError::Db(s.into())),
-		}
-	}
-}
-
-// ----
-
-struct SledTx<'a> {
-	trees: &'a [TransactionalTree],
-	err: Cell<Option<UnabortableTransactionError>>,
-}
-
-impl<'a> SledTx<'a> {
-	fn get_tree(&self, i: usize) -> TxOpResult<&TransactionalTree> {
-		self.trees.get(i).ok_or_else(|| {
-			TxOpError(Error(
-				"invalid tree id (it might have been openned after the transaction started)".into(),
-			))
-		})
-	}
-
-	fn save_error<R>(
-		&self,
-		v: std::result::Result<R, UnabortableTransactionError>,
-	) -> TxOpResult<R> {
-		match v {
-			Ok(x) => Ok(x),
-			Err(e) => {
-				let txt = format!("{}", e);
-				self.err.set(Some(e));
-				Err(TxOpError(Error(txt.into())))
-			}
-		}
-	}
-}
-
-impl<'a> ITx for SledTx<'a> {
-	fn get(&self, tree: usize, key: &[u8]) -> TxOpResult<Option<Value>> {
-		let tree = self.get_tree(tree)?;
-		let tmp = self.save_error(tree.get(key))?;
-		Ok(tmp.map(|x| x.to_vec()))
-	}
-	fn len(&self, _tree: usize) -> TxOpResult<usize> {
-		unimplemented!(".len() in transaction not supported with Sled backend")
-	}
-
-	fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> TxOpResult<Option<Value>> {
-		let tree = self.get_tree(tree)?;
-		let old_val = self.save_error(tree.insert(key, value))?;
-		Ok(old_val.map(|x| x.to_vec()))
-	}
-	fn remove(&mut self, tree: usize, key: &[u8]) -> TxOpResult<Option<Value>> {
-		let tree = self.get_tree(tree)?;
-		let old_val = self.save_error(tree.remove(key))?;
-		Ok(old_val.map(|x| x.to_vec()))
-	}
-
-	fn iter(&self, _tree: usize) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!("Iterators in transactions not supported with Sled backend");
-	}
-	fn iter_rev(&self, _tree: usize) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!("Iterators in transactions not supported with Sled backend");
-	}
-
-	fn range<'r>(
-		&self,
-		_tree: usize,
-		_low: Bound<&'r [u8]>,
-		_high: Bound<&'r [u8]>,
-	) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!("Iterators in transactions not supported with Sled backend");
-	}
-	fn range_rev<'r>(
-		&self,
-		_tree: usize,
-		_low: Bound<&'r [u8]>,
-		_high: Bound<&'r [u8]>,
-	) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!("Iterators in transactions not supported with Sled backend");
-	}
-}
diff --git a/src/db/sqlite_adapter.rs b/src/db/sqlite_adapter.rs
index 9f967c66..6c556c97 100644
--- a/src/db/sqlite_adapter.rs
+++ b/src/db/sqlite_adapter.rs
@@ -144,10 +144,6 @@ impl IDb for SqliteDb {
 		}
 	}
 
-	fn fast_len(&self, tree: usize) -> Result<Option<usize>> {
-		Ok(Some(self.len(tree)?))
-	}
-
 	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<Option<Value>> {
 		trace!("insert {}: lock db", tree);
 		let this = self.0.lock().unwrap();
@@ -367,33 +363,64 @@ impl<'a> ITx for SqliteTx<'a> {
 
 		Ok(old_val)
 	}
+	fn clear(&mut self, tree: usize) -> TxOpResult<()> {
+		let tree = self.get_tree(tree)?;
+		self.tx.execute(&format!("DELETE FROM {}", tree), [])?;
+		Ok(())
+	}
 
-	fn iter(&self, _tree: usize) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!();
+	fn iter(&self, tree: usize) -> TxOpResult<TxValueIter<'_>> {
+		let tree = self.get_tree(tree)?;
+		let sql = format!("SELECT k, v FROM {} ORDER BY k ASC", tree);
+		TxValueIterator::make(self, &sql, [])
 	}
-	fn iter_rev(&self, _tree: usize) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!();
+	fn iter_rev(&self, tree: usize) -> TxOpResult<TxValueIter<'_>> {
+		let tree = self.get_tree(tree)?;
+		let sql = format!("SELECT k, v FROM {} ORDER BY k DESC", tree);
+		TxValueIterator::make(self, &sql, [])
 	}
 
 	fn range<'r>(
 		&self,
-		_tree: usize,
-		_low: Bound<&'r [u8]>,
-		_high: Bound<&'r [u8]>,
+		tree: usize,
+		low: Bound<&'r [u8]>,
+		high: Bound<&'r [u8]>,
 	) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!();
+		let tree = self.get_tree(tree)?;
+
+		let (bounds_sql, params) = bounds_sql(low, high);
+		let sql = format!("SELECT k, v FROM {} {} ORDER BY k ASC", tree, bounds_sql);
+
+		let params = params
+			.iter()
+			.map(|x| x as &dyn rusqlite::ToSql)
+			.collect::<Vec<_>>();
+
+		TxValueIterator::make::<&[&dyn rusqlite::ToSql]>(self, &sql, params.as_ref())
 	}
 	fn range_rev<'r>(
 		&self,
-		_tree: usize,
-		_low: Bound<&'r [u8]>,
-		_high: Bound<&'r [u8]>,
+		tree: usize,
+		low: Bound<&'r [u8]>,
+		high: Bound<&'r [u8]>,
 	) -> TxOpResult<TxValueIter<'_>> {
-		unimplemented!();
+		let tree = self.get_tree(tree)?;
+
+		let (bounds_sql, params) = bounds_sql(low, high);
+		let sql = format!("SELECT k, v FROM {} {} ORDER BY k DESC", tree, bounds_sql);
+
+		let params = params
+			.iter()
+			.map(|x| x as &dyn rusqlite::ToSql)
+			.collect::<Vec<_>>();
+
+		TxValueIterator::make::<&[&dyn rusqlite::ToSql]>(self, &sql, params.as_ref())
 	}
 }
 
-// ----
+// ---- iterators outside transactions ----
+// complicated, they must hold the Statement and Row objects
+// therefore quite some unsafe code (it is a self-referential struct)
 
 struct DbValueIterator<'a> {
 	db: MutexGuard<'a, SqliteDbInner>,
@@ -417,17 +444,23 @@ impl<'a> DbValueIterator<'a> {
 		let mut boxed = Box::pin(res);
 		trace!("make iterator with sql: {}", sql);
 
-		unsafe {
-			let db = NonNull::from(&boxed.db);
-			let stmt = db.as_ref().db.prepare(sql)?;
+		// This unsafe allows us to bypass lifetime checks
+		let db = unsafe { NonNull::from(&boxed.db).as_ref() };
+		let stmt = db.db.prepare(sql)?;
 
-			let mut_ref: Pin<&mut DbValueIterator<'a>> = Pin::as_mut(&mut boxed);
+		let mut_ref = Pin::as_mut(&mut boxed);
+		// This unsafe allows us to write in a field of the pinned struct
+		unsafe {
 			Pin::get_unchecked_mut(mut_ref).stmt = Some(stmt);
+		}
 
-			let mut stmt = NonNull::from(&boxed.stmt);
-			let iter = stmt.as_mut().as_mut().unwrap().query(args)?;
+		// This unsafe allows us to bypass lifetime checks
+		let stmt = unsafe { NonNull::from(&boxed.stmt).as_mut() };
+		let iter = stmt.as_mut().unwrap().query(args)?;
 
-			let mut_ref: Pin<&mut DbValueIterator<'a>> = Pin::as_mut(&mut boxed);
+		let mut_ref = Pin::as_mut(&mut boxed);
+		// This unsafe allows us to write in a field of the pinned struct
+		unsafe {
 			Pin::get_unchecked_mut(mut_ref).iter = Some(iter);
 		}
 
@@ -449,28 +482,73 @@ impl<'a> Iterator for DbValueIteratorPin<'a> {
 	type Item = Result<(Value, Value)>;
 
 	fn next(&mut self) -> Option<Self::Item> {
-		let next = unsafe {
-			let mut_ref: Pin<&mut DbValueIterator<'a>> = Pin::as_mut(&mut self.0);
-			Pin::get_unchecked_mut(mut_ref).iter.as_mut()?.next()
-		};
-		let row = match next {
-			Err(e) => return Some(Err(e.into())),
-			Ok(None) => return None,
-			Ok(Some(r)) => r,
-		};
-		let k = match row.get::<_, Vec<u8>>(0) {
-			Err(e) => return Some(Err(e.into())),
-			Ok(x) => x,
-		};
-		let v = match row.get::<_, Vec<u8>>(1) {
-			Err(e) => return Some(Err(e.into())),
-			Ok(y) => y,
+		let mut_ref = Pin::as_mut(&mut self.0);
+		// This unsafe allows us to mutably access the iterator field
+		let next = unsafe { Pin::get_unchecked_mut(mut_ref).iter.as_mut()?.next() };
+		iter_next_row(next)
+	}
+}
+
+// ---- iterators within transactions ----
+// it's the same except we don't hold a mutex guard,
+// only a Statement and a Rows object
+
+struct TxValueIterator<'a> {
+	stmt: Statement<'a>,
+	iter: Option<Rows<'a>>,
+	_pin: PhantomPinned,
+}
+
+impl<'a> TxValueIterator<'a> {
+	fn make<P: rusqlite::Params>(
+		tx: &'a SqliteTx<'a>,
+		sql: &str,
+		args: P,
+	) -> TxOpResult<TxValueIter<'a>> {
+		let stmt = tx.tx.prepare(sql)?;
+		let res = TxValueIterator {
+			stmt,
+			iter: None,
+			_pin: PhantomPinned,
 		};
-		Some(Ok((k, v)))
+		let mut boxed = Box::pin(res);
+		trace!("make iterator with sql: {}", sql);
+
+		// This unsafe allows us to bypass lifetime checks
+		let stmt = unsafe { NonNull::from(&boxed.stmt).as_mut() };
+		let iter = stmt.query(args)?;
+
+		let mut_ref = Pin::as_mut(&mut boxed);
+		// This unsafe allows us to write in a field of the pinned struct
+		unsafe {
+			Pin::get_unchecked_mut(mut_ref).iter = Some(iter);
+		}
+
+		Ok(Box::new(TxValueIteratorPin(boxed)))
 	}
 }
 
-// ----
+impl<'a> Drop for TxValueIterator<'a> {
+	fn drop(&mut self) {
+		trace!("drop iter");
+		drop(self.iter.take());
+	}
+}
+
+struct TxValueIteratorPin<'a>(Pin<Box<TxValueIterator<'a>>>);
+
+impl<'a> Iterator for TxValueIteratorPin<'a> {
+	type Item = TxOpResult<(Value, Value)>;
+
+	fn next(&mut self) -> Option<Self::Item> {
+		let mut_ref = Pin::as_mut(&mut self.0);
+		// This unsafe allows us to mutably access the iterator field
+		let next = unsafe { Pin::get_unchecked_mut(mut_ref).iter.as_mut()?.next() };
+		iter_next_row(next)
+	}
+}
+
+// ---- utility ----
 
 fn bounds_sql<'r>(low: Bound<&'r [u8]>, high: Bound<&'r [u8]>) -> (String, Vec<Vec<u8>>) {
 	let mut sql = String::new();
@@ -510,3 +588,25 @@ fn bounds_sql<'r>(low: Bound<&'r [u8]>, high: Bound<&'r [u8]>) -> (String, Vec<V
 
 	(sql, params)
 }
+
+fn iter_next_row<E>(
+	next_row: rusqlite::Result<Option<&rusqlite::Row>>,
+) -> Option<std::result::Result<(Value, Value), E>>
+where
+	E: From<rusqlite::Error>,
+{
+	let row = match next_row {
+		Err(e) => return Some(Err(e.into())),
+		Ok(None) => return None,
+		Ok(Some(r)) => r,
+	};
+	let k = match row.get::<_, Vec<u8>>(0) {
+		Err(e) => return Some(Err(e.into())),
+		Ok(x) => x,
+	};
+	let v = match row.get::<_, Vec<u8>>(1) {
+		Err(e) => return Some(Err(e.into())),
+		Ok(y) => y,
+	};
+	Some(Ok((k, v)))
+}
diff --git a/src/db/test.rs b/src/db/test.rs
index cd99eafa..3add89fb 100644
--- a/src/db/test.rs
+++ b/src/db/test.rs
@@ -10,8 +10,13 @@ fn test_suite(db: Db) {
 	let vb: &[u8] = &b"plip"[..];
 	let vc: &[u8] = &b"plup"[..];
 
+	// ---- test simple insert/delete ----
+
 	assert!(tree.insert(ka, va).unwrap().is_none());
 	assert_eq!(tree.get(ka).unwrap().unwrap(), va);
+	assert_eq!(tree.len().unwrap(), 1);
+
+	// ---- test transaction logic ----
 
 	let res = db.transaction::<_, (), _>(|tx| {
 		assert_eq!(tx.get(&tree, ka).unwrap().unwrap(), va);
@@ -37,6 +42,8 @@ fn test_suite(db: Db) {
 	assert!(matches!(res, Err(TxError::Abort(42))));
 	assert_eq!(tree.get(ka).unwrap().unwrap(), vb);
 
+	// ---- test iteration outside of transactions ----
+
 	let mut iter = tree.iter().unwrap();
 	let next = iter.next().unwrap().unwrap();
 	assert_eq!((next.0.as_ref(), next.1.as_ref()), (ka, vb));
@@ -73,6 +80,48 @@ fn test_suite(db: Db) {
 	assert_eq!((next.0.as_ref(), next.1.as_ref()), (ka, vb));
 	assert!(iter.next().is_none());
 	drop(iter);
+
+	// ---- test iteration within transactions ----
+
+	db.transaction::<_, (), _>(|tx| {
+		let mut iter = tx.iter(&tree).unwrap();
+		let next = iter.next().unwrap().unwrap();
+		assert_eq!((next.0.as_ref(), next.1.as_ref()), (ka, vb));
+		let next = iter.next().unwrap().unwrap();
+		assert_eq!((next.0.as_ref(), next.1.as_ref()), (kb, vc));
+		assert!(iter.next().is_none());
+		Ok(())
+	})
+	.unwrap();
+
+	db.transaction::<_, (), _>(|tx| {
+		let mut iter = tx.range(&tree, kint..).unwrap();
+		let next = iter.next().unwrap().unwrap();
+		assert_eq!((next.0.as_ref(), next.1.as_ref()), (kb, vc));
+		assert!(iter.next().is_none());
+		Ok(())
+	})
+	.unwrap();
+
+	db.transaction::<_, (), _>(|tx| {
+		let mut iter = tx.range_rev(&tree, ..kint).unwrap();
+		let next = iter.next().unwrap().unwrap();
+		assert_eq!((next.0.as_ref(), next.1.as_ref()), (ka, vb));
+		assert!(iter.next().is_none());
+		Ok(())
+	})
+	.unwrap();
+
+	db.transaction::<_, (), _>(|tx| {
+		let mut iter = tx.iter_rev(&tree).unwrap();
+		let next = iter.next().unwrap().unwrap();
+		assert_eq!((next.0.as_ref(), next.1.as_ref()), (kb, vc));
+		let next = iter.next().unwrap().unwrap();
+		assert_eq!((next.0.as_ref(), next.1.as_ref()), (ka, vb));
+		assert!(iter.next().is_none());
+		Ok(())
+	})
+	.unwrap();
 }
 
 #[test]
@@ -91,17 +140,6 @@ fn test_lmdb_db() {
 }
 
 #[test]
-#[cfg(feature = "sled")]
-fn test_sled_db() {
-	use crate::sled_adapter::SledDb;
-
-	let path = mktemp::Temp::new_dir().unwrap();
-	let db = SledDb::init(sled::open(path.to_path_buf()).unwrap());
-	test_suite(db);
-	drop(path);
-}
-
-#[test]
 #[cfg(feature = "sqlite")]
 fn test_sqlite_db() {
 	use crate::sqlite_adapter::SqliteDb;