rust-nodemap: insert method

In this implementation, we are in direct competition
with the C version: this Rust version will have a clear
startup advantage because it will read the data from disk,
but the insertion happens all in memory for both.

Differential Revision: https://phab.mercurial-scm.org/D7795

rust/hg-core/src/revlog/nodemap.rs

@@ -1,526 +1,790 b''
 // Copyright 2018-2020 Georges Racinet <[e-mail]>
 //           and Mercurial contributors
 //
 // This software may be used and distributed according to the terms of the
 // GNU General Public License version 2 or any later version.
 //! Indexing facilities for fast retrieval of `Revision` from `Node`
 //!
 //! This provides a variation on the 16-ary radix tree that is
 //! provided as "nodetree" in revlog.c, ready for append-only persistence
 //! on disk.
 //!
 //! Following existing implicit conventions, the "nodemap" terminology
 //! is used in a more abstract context.
 
 use super::{
     Node, NodeError, NodePrefix, NodePrefixRef, Revision, RevlogIndex,
 };
+
 use std::fmt;
 use std::ops::Deref;
 use std::ops::Index;
 
 #[derive(Debug, PartialEq)]
 pub enum NodeMapError {
     MultipleResults,
     InvalidNodePrefix(NodeError),
     /// A `Revision` stored in the nodemap could not be found in the index
     RevisionNotInIndex(Revision),
 }
 
 impl From<NodeError> for NodeMapError {
     fn from(err: NodeError) -> Self {
         NodeMapError::InvalidNodePrefix(err)
     }
 }
 
 /// Mapping system from Mercurial nodes to revision numbers.
 ///
 /// ## `RevlogIndex` and `NodeMap`
 ///
 /// One way to think about their relationship is that
 /// the `NodeMap` is a prefix-oriented reverse index of the `Node` information
 /// carried by a [`RevlogIndex`].
 ///
 /// Many of the methods in this trait take a `RevlogIndex` argument
 /// which is used for validation of their results. This index must naturally
 /// be the one the `NodeMap` is about, and it must be consistent.
 ///
 /// Notably, the `NodeMap` must not store
 /// information about more `Revision` values than there are in the index.
 /// In these methods, an encountered `Revision` is not in the index, a
 /// [`RevisionNotInIndex`] error is returned.
 ///
 /// In insert operations, the rule is thus that the `NodeMap` must always
 /// be updated after the `RevlogIndex`
 /// be updated first, and the `NodeMap` second.
 ///
 /// [`RevisionNotInIndex`]: enum.NodeMapError.html#variant.RevisionNotInIndex
 /// [`RevlogIndex`]: ../trait.RevlogIndex.html
 pub trait NodeMap {
     /// Find the unique `Revision` having the given `Node`
     ///
     /// If no Revision matches the given `Node`, `Ok(None)` is returned.
     fn find_node(
         &self,
         index: &impl RevlogIndex,
         node: &Node,
     ) -> Result<Option<Revision>, NodeMapError> {
         self.find_bin(index, node.into())
     }
 
     /// Find the unique Revision whose `Node` starts with a given binary prefix
     ///
     /// If no Revision matches the given prefix, `Ok(None)` is returned.
     ///
     /// If several Revisions match the given prefix, a [`MultipleResults`]
     /// error is returned.
     fn find_bin<'a>(
         &self,
         idx: &impl RevlogIndex,
         prefix: NodePrefixRef<'a>,
     ) -> Result<Option<Revision>, NodeMapError>;
 
     /// Find the unique Revision whose `Node` hexadecimal string representation
     /// starts with a given prefix
     ///
     /// If no Revision matches the given prefix, `Ok(None)` is returned.
     ///
     /// If several Revisions match the given prefix, a [`MultipleResults`]
     /// error is returned.
     fn find_hex(
         &self,
         idx: &impl RevlogIndex,
         prefix: &str,
     ) -> Result<Option<Revision>, NodeMapError> {
         self.find_bin(idx, NodePrefix::from_hex(prefix)?.borrow())
     }
 }
 
+pub trait MutableNodeMap: NodeMap {
+    fn insert<I: RevlogIndex>(
+        &mut self,
+        index: &I,
+        node: &Node,
+        rev: Revision,
+    ) -> Result<(), NodeMapError>;
+}
+
 /// Low level NodeTree [`Blocks`] elements
 ///
 /// These are exactly as for instance on persistent storage.
 type RawElement = i32;
 
 /// High level representation of values in NodeTree
 /// [`Blocks`](struct.Block.html)
 ///
 /// This is the high level representation that most algorithms should
 /// use.
 #[derive(Clone, Debug, Eq, PartialEq)]
 enum Element {
     Rev(Revision),
     Block(usize),
     None,
 }
 
 impl From<RawElement> for Element {
     /// Conversion from low level representation, after endianness conversion.
     ///
     /// See [`Block`](struct.Block.html) for explanation about the encoding.
     fn from(raw: RawElement) -> Element {
         if raw >= 0 {
             Element::Block(raw as usize)
         } else if raw == -1 {
             Element::None
         } else {
             Element::Rev(-raw - 2)
         }
     }
 }
 
 impl From<Element> for RawElement {
     fn from(element: Element) -> RawElement {
         match element {
             Element::None => 0,
             Element::Block(i) => i as RawElement,
             Element::Rev(rev) => -rev - 2,
         }
     }
 }
 
 /// A logical block of the `NodeTree`, packed with a fixed size.
 ///
 /// These are always used in container types implementing `Index<Block>`,
 /// such as `&Block`
 ///
 /// As an array of integers, its ith element encodes that the
 /// ith potential edge from the block, representing the ith hexadecimal digit
 /// (nybble) `i` is either:
 ///
 /// - absent (value -1)
 /// - another `Block` in the same indexable container (value ≥ 0)
 ///  - a `Revision` leaf (value ≤ -2)
 ///
 /// Endianness has to be fixed for consistency on shared storage across
 /// different architectures.
 ///
 /// A key difference with the C `nodetree` is that we need to be
 /// able to represent the [`Block`] at index 0, hence -1 is the empty marker
 /// rather than 0 and the `Revision` range upper limit of -2 instead of -1.
 ///
 /// Another related difference is that `NULL_REVISION` (-1) is not
 /// represented at all, because we want an immutable empty nodetree
 /// to be valid.
 
 #[derive(Clone, PartialEq)]
 pub struct Block([RawElement; 16]);
 
 impl Block {
     fn new() -> Self {
         Block([-1; 16])
     }
 
     fn get(&self, nybble: u8) -> Element {
         Element::from(RawElement::from_be(self.0[nybble as usize]))
     }
 
     fn set(&mut self, nybble: u8, element: Element) {
         self.0[nybble as usize] = RawElement::to_be(element.into())
     }
 }
 
 impl fmt::Debug for Block {
     /// sparse representation for testing and debugging purposes
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_map()
             .entries((0..16).filter_map(|i| match self.get(i) {
                 Element::None => None,
                 element => Some((i, element)),
             }))
             .finish()
     }
 }
 
 /// A mutable 16-radix tree with the root block logically at the end
 ///
 /// Because of the append only nature of our node trees, we need to
 /// keep the original untouched and store new blocks separately.
 ///
 /// The mutable root `Block` is kept apart so that we don't have to rebump
 /// it on each insertion.
 pub struct NodeTree {
     readonly: Box<dyn Deref<Target = [Block]> + Send>,
     growable: Vec<Block>,
     root: Block,
 }
 
 impl Index<usize> for NodeTree {
     type Output = Block;
 
     fn index(&self, i: usize) -> &Block {
         let ro_len = self.readonly.len();
         if i < ro_len {
             &self.readonly[i]
         } else if i == ro_len + self.growable.len() {
             &self.root
         } else {
             &self.growable[i - ro_len]
         }
     }
 }
 
 /// Return `None` unless the `Node` for `rev` has given prefix in `index`.
 fn has_prefix_or_none<'p>(
     idx: &impl RevlogIndex,
     prefix: NodePrefixRef<'p>,
     rev: Revision,
 ) -> Result<Option<Revision>, NodeMapError> {
     idx.node(rev)
         .ok_or_else(|| NodeMapError::RevisionNotInIndex(rev))
         .map(|node| {
             if prefix.is_prefix_of(node) {
                 Some(rev)
             } else {
                 None
             }
         })
 }
 
 impl NodeTree {
     /// Initiate a NodeTree from an immutable slice-like of `Block`
     ///
     /// We keep `readonly` and clone its root block if it isn't empty.
     fn new(readonly: Box<dyn Deref<Target = [Block]> + Send>) -> Self {
         let root = readonly
             .last()
             .map(|b| b.clone())
             .unwrap_or_else(|| Block::new());
         NodeTree {
             readonly: readonly,
             growable: Vec::new(),
             root: root,
         }
     }
 
     /// Total number of blocks
     fn len(&self) -> usize {
         self.readonly.len() + self.growable.len() + 1
     }
 
     /// Implemented for completeness
     ///
     /// A `NodeTree` always has at least the mutable root block.
     #[allow(dead_code)]
     fn is_empty(&self) -> bool {
         false
     }
 
     /// Main working method for `NodeTree` searches
     ///
     /// This partial implementation lacks special cases for NULL_REVISION
     fn lookup<'p>(
         &self,
         prefix: NodePrefixRef<'p>,
     ) -> Result<Option<Revision>, NodeMapError> {
         for visit_item in self.visit(prefix) {
             if let Some(opt) = visit_item.final_revision() {
                 return Ok(opt);
             }
         }
         Err(NodeMapError::MultipleResults)
     }
 
     fn visit<'n, 'p>(
         &'n self,
         prefix: NodePrefixRef<'p>,
     ) -> NodeTreeVisitor<'n, 'p> {
         NodeTreeVisitor {
             nt: self,
             prefix: prefix,
             visit: self.len() - 1,
             nybble_idx: 0,
             done: false,
         }
     }
+    /// Return a mutable reference for `Block` at index `idx`.
+    ///
+    /// If `idx` lies in the immutable area, then the reference is to
+    /// a newly appended copy.
+    ///
+    /// Returns (new_idx, glen, mut_ref) where
+    ///
+    /// - `new_idx` is the index of the mutable `Block`
+    /// - `mut_ref` is a mutable reference to the mutable Block.
+    /// - `glen` is the new length of `self.growable`
+    ///
+    /// Note: the caller wouldn't be allowed to query `self.growable.len()`
+    /// itself because of the mutable borrow taken with the returned `Block`
+    fn mutable_block(&mut self, idx: usize) -> (usize, &mut Block, usize) {
+        let ro_blocks = &self.readonly;
+        let ro_len = ro_blocks.len();
+        let glen = self.growable.len();
+        if idx < ro_len {
+            // TODO OPTIM I think this makes two copies
+            self.growable.push(ro_blocks[idx].clone());
+            (glen + ro_len, &mut self.growable[glen], glen + 1)
+        } else if glen + ro_len == idx {
+            (idx, &mut self.root, glen)
+        } else {
+            (idx, &mut self.growable[idx - ro_len], glen)
+        }
+    }
+
+    /// Main insertion method
+    ///
+    /// This will dive in the node tree to find the deepest `Block` for
+    /// `node`, split it as much as needed and record `node` in there.
+    /// The method then backtracks, updating references in all the visited
+    /// blocks from the root.
+    ///
+    /// All the mutated `Block` are copied first to the growable part if
+    /// needed. That happens for those in the immutable part except the root.
+    pub fn insert<I: RevlogIndex>(
+        &mut self,
+        index: &I,
+        node: &Node,
+        rev: Revision,
+    ) -> Result<(), NodeMapError> {
+        let ro_len = &self.readonly.len();
+
+        let mut visit_steps: Vec<_> = self.visit(node.into()).collect();
+        let read_nybbles = visit_steps.len();
+        // visit_steps cannot be empty, since we always visit the root block
+        let deepest = visit_steps.pop().unwrap();
+
+        let (mut block_idx, mut block, mut glen) =
+            self.mutable_block(deepest.block_idx);
+
+        if let Element::Rev(old_rev) = deepest.element {
+            let old_node = index
+                .node(old_rev)
+                .ok_or_else(|| NodeMapError::RevisionNotInIndex(old_rev))?;
+            if old_node == node {
+                return Ok(()); // avoid creating lots of useless blocks
+            }
+
+            // Looping over the tail of nybbles in both nodes, creating
+            // new blocks until we find the difference
+            let mut new_block_idx = ro_len + glen;
+            let mut nybble = deepest.nybble;
+            for nybble_pos in read_nybbles..node.nybbles_len() {
+                block.set(nybble, Element::Block(new_block_idx));
+
+                let new_nybble = node.get_nybble(nybble_pos);
+                let old_nybble = old_node.get_nybble(nybble_pos);
+
+                if old_nybble == new_nybble {
+                    self.growable.push(Block::new());
+                    block = &mut self.growable[glen];
+                    glen += 1;
+                    new_block_idx += 1;
+                    nybble = new_nybble;
+                } else {
+                    let mut new_block = Block::new();
+                    new_block.set(old_nybble, Element::Rev(old_rev));
+                    new_block.set(new_nybble, Element::Rev(rev));
+                    self.growable.push(new_block);
+                    break;
+                }
+            }
+        } else {
+            // Free slot in the deepest block: no splitting has to be done
+            block.set(deepest.nybble, Element::Rev(rev));
+        }
+
+        // Backtrack over visit steps to update references
+        while let Some(visited) = visit_steps.pop() {
+            let to_write = Element::Block(block_idx);
+            if visit_steps.is_empty() {
+                self.root.set(visited.nybble, to_write);
+                break;
+            }
+            let (new_idx, block, _) = self.mutable_block(visited.block_idx);
+            if block.get(visited.nybble) == to_write {
+                break;
+            }
+            block.set(visited.nybble, to_write);
+            block_idx = new_idx;
+        }
+        Ok(())
+    }
 }
 
 struct NodeTreeVisitor<'n, 'p> {
     nt: &'n NodeTree,
     prefix: NodePrefixRef<'p>,
     visit: usize,
     nybble_idx: usize,
     done: bool,
 }
 
 #[derive(Debug, PartialEq, Clone)]
 struct NodeTreeVisitItem {
     block_idx: usize,
     nybble: u8,
     element: Element,
 }
 
 impl<'n, 'p> Iterator for NodeTreeVisitor<'n, 'p> {
     type Item = NodeTreeVisitItem;
 
     fn next(&mut self) -> Option<Self::Item> {
         if self.done || self.nybble_idx >= self.prefix.len() {
             return None;
         }
 
         let nybble = self.prefix.get_nybble(self.nybble_idx);
         self.nybble_idx += 1;
 
         let visit = self.visit;
         let element = self.nt[visit].get(nybble);
         if let Element::Block(idx) = element {
             self.visit = idx;
         } else {
             self.done = true;
         }
 
         Some(NodeTreeVisitItem {
             block_idx: visit,
             nybble: nybble,
             element: element,
         })
     }
 }
 
 impl NodeTreeVisitItem {
     // Return `Some(opt)` if this item is final, with `opt` being the
     // `Revision` that it may represent.
     //
     // If the item is not terminal, return `None`
     fn final_revision(&self) -> Option<Option<Revision>> {
         match self.element {
             Element::Block(_) => None,
             Element::Rev(r) => Some(Some(r)),
             Element::None => Some(None),
         }
     }
 }
 
 impl From<Vec<Block>> for NodeTree {
     fn from(vec: Vec<Block>) -> Self {
         Self::new(Box::new(vec))
     }
 }
 
 impl fmt::Debug for NodeTree {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let readonly: &[Block] = &*self.readonly;
         write!(
             f,
             "readonly: {:?}, growable: {:?}, root: {:?}",
             readonly, self.growable, self.root
         )
     }
 }
 
+impl Default for NodeTree {
+    /// Create a fully mutable empty NodeTree
+    fn default() -> Self {
+        NodeTree::new(Box::new(Vec::new()))
+    }
+}
+
 impl NodeMap for NodeTree {
     fn find_bin<'a>(
         &self,
         idx: &impl RevlogIndex,
         prefix: NodePrefixRef<'a>,
     ) -> Result<Option<Revision>, NodeMapError> {
         self.lookup(prefix.clone()).and_then(|opt| {
             opt.map_or(Ok(None), |rev| has_prefix_or_none(idx, prefix, rev))
         })
     }
 }
 
 #[cfg(test)]
 mod tests {
     use super::NodeMapError::*;
     use super::*;
     use crate::revlog::node::{hex_pad_right, Node};
     use std::collections::HashMap;
 
     /// Creates a `Block` using a syntax close to the `Debug` output
     macro_rules! block {
         {$($nybble:tt : $variant:ident($val:tt)),*} => (
             {
                 let mut block = Block::new();
                 $(block.set($nybble, Element::$variant($val)));*;
                 block
             }
         )
     }
 
     #[test]
     fn test_block_debug() {
         let mut block = Block::new();
         block.set(1, Element::Rev(3));
         block.set(10, Element::Block(0));
         assert_eq!(format!("{:?}", block), "{1: Rev(3), 10: Block(0)}");
     }
 
     #[test]
     fn test_block_macro() {
         let block = block! {5: Block(2)};
         assert_eq!(format!("{:?}", block), "{5: Block(2)}");
 
         let block = block! {13: Rev(15), 5: Block(2)};
         assert_eq!(format!("{:?}", block), "{5: Block(2), 13: Rev(15)}");
     }
 
     #[test]
     fn test_raw_block() {
         let mut raw = [-1; 16];
         raw[0] = 0;
         raw[1] = RawElement::to_be(15);
         raw[2] = RawElement::to_be(-2);
         raw[3] = RawElement::to_be(-1);
         raw[4] = RawElement::to_be(-3);
         let block = Block(raw);
         assert_eq!(block.get(0), Element::Block(0));
         assert_eq!(block.get(1), Element::Block(15));
         assert_eq!(block.get(3), Element::None);
         assert_eq!(block.get(2), Element::Rev(0));
         assert_eq!(block.get(4), Element::Rev(1));
     }
 
     type TestIndex = HashMap<Revision, Node>;
 
     impl RevlogIndex for TestIndex {
         fn node(&self, rev: Revision) -> Option<&Node> {
             self.get(&rev)
         }
 
         fn len(&self) -> usize {
             self.len()
         }
     }
 
-    /// Pad hexadecimal Node prefix with zeros on the right, then insert
+    /// Pad hexadecimal Node prefix with zeros on the right
     ///
     /// This avoids having to repeatedly write very long hexadecimal
     /// strings for test data, and brings actual hash size independency.
+    #[cfg(test)]
+    fn pad_node(hex: &str) -> Node {
+        Node::from_hex(&hex_pad_right(hex)).unwrap()
+    }
+
+    /// Pad hexadecimal Node prefix with zeros on the right, then insert
     fn pad_insert(idx: &mut TestIndex, rev: Revision, hex: &str) {
-        idx.insert(rev, Node::from_hex(&hex_pad_right(hex)).unwrap());
+        idx.insert(rev, pad_node(hex));
     }
 
     fn sample_nodetree() -> NodeTree {
         NodeTree::from(vec![
             block![0: Rev(9)],
             block![0: Rev(0), 1: Rev(9)],
             block![0: Block(1), 1:Rev(1)],
         ])
     }
 
     #[test]
     fn test_nt_debug() {
         let nt = sample_nodetree();
         assert_eq!(
             format!("{:?}", nt),
             "readonly: \
              [{0: Rev(9)}, {0: Rev(0), 1: Rev(9)}, {0: Block(1), 1: Rev(1)}], \
              growable: [], \
              root: {0: Block(1), 1: Rev(1)}",
         );
     }
 
     #[test]
     fn test_immutable_find_simplest() -> Result<(), NodeMapError> {
         let mut idx: TestIndex = HashMap::new();
         pad_insert(&mut idx, 1, "1234deadcafe");
 
         let nt = NodeTree::from(vec![block! {1: Rev(1)}]);
         assert_eq!(nt.find_hex(&idx, "1")?, Some(1));
         assert_eq!(nt.find_hex(&idx, "12")?, Some(1));
         assert_eq!(nt.find_hex(&idx, "1234de")?, Some(1));
         assert_eq!(nt.find_hex(&idx, "1a")?, None);
         assert_eq!(nt.find_hex(&idx, "ab")?, None);
 
         // and with full binary Nodes
         assert_eq!(nt.find_node(&idx, idx.get(&1).unwrap())?, Some(1));
         let unknown = Node::from_hex(&hex_pad_right("3d")).unwrap();
         assert_eq!(nt.find_node(&idx, &unknown)?, None);
         Ok(())
     }
 
     #[test]
     fn test_immutable_find_one_jump() {
         let mut idx = TestIndex::new();
         pad_insert(&mut idx, 9, "012");
         pad_insert(&mut idx, 0, "00a");
 
         let nt = sample_nodetree();
 
         assert_eq!(nt.find_hex(&idx, "0"), Err(MultipleResults));
         assert_eq!(nt.find_hex(&idx, "01"), Ok(Some(9)));
         assert_eq!(nt.find_hex(&idx, "00"), Ok(Some(0)));
         assert_eq!(nt.find_hex(&idx, "00a"), Ok(Some(0)));
     }
 
     #[test]
     fn test_mutated_find() -> Result<(), NodeMapError> {
         let mut idx = TestIndex::new();
         pad_insert(&mut idx, 9, "012");
         pad_insert(&mut idx, 0, "00a");
         pad_insert(&mut idx, 2, "cafe");
         pad_insert(&mut idx, 3, "15");
         pad_insert(&mut idx, 1, "10");
 
         let nt = NodeTree {
             readonly: sample_nodetree().readonly,
             growable: vec![block![0: Rev(1), 5: Rev(3)]],
             root: block![0: Block(1), 1:Block(3), 12: Rev(2)],
         };
         assert_eq!(nt.find_hex(&idx, "10")?, Some(1));
         assert_eq!(nt.find_hex(&idx, "c")?, Some(2));
         assert_eq!(nt.find_hex(&idx, "00")?, Some(0));
         assert_eq!(nt.find_hex(&idx, "01")?, Some(9));
         Ok(())
     }
+
+    struct TestNtIndex {
+        index: TestIndex,
+        nt: NodeTree,
+    }
+
+    impl TestNtIndex {
+        fn new() -> Self {
+            TestNtIndex {
+                index: HashMap::new(),
+                nt: NodeTree::default(),
+            }
+        }
+
+        fn insert(
+            &mut self,
+            rev: Revision,
+            hex: &str,
+        ) -> Result<(), NodeMapError> {
+            let node = pad_node(hex);
+            self.index.insert(rev, node.clone());
+            self.nt.insert(&self.index, &node, rev)?;
+            Ok(())
+        }
+
+        fn find_hex(
+            &self,
+            prefix: &str,
+        ) -> Result<Option<Revision>, NodeMapError> {
+            self.nt.find_hex(&self.index, prefix)
+        }
+
+        /// Drain `added` and restart a new one
+        fn commit(self) -> Self {
+            let mut as_vec: Vec<Block> =
+                self.nt.readonly.iter().map(|block| block.clone()).collect();
+            as_vec.extend(self.nt.growable);
+            as_vec.push(self.nt.root);
+
+            Self {
+                index: self.index,
+                nt: NodeTree::from(as_vec).into(),
+            }
+        }
+    }
+
+    #[test]
+    fn test_insert_full_mutable() -> Result<(), NodeMapError> {
+        let mut idx = TestNtIndex::new();
+        idx.insert(0, "1234")?;
+        assert_eq!(idx.find_hex("1")?, Some(0));
+        assert_eq!(idx.find_hex("12")?, Some(0));
+
+        // let's trigger a simple split
+        idx.insert(1, "1a34")?;
+        assert_eq!(idx.nt.growable.len(), 1);
+        assert_eq!(idx.find_hex("12")?, Some(0));
+        assert_eq!(idx.find_hex("1a")?, Some(1));
+
+        // reinserting is a no_op
+        idx.insert(1, "1a34")?;
+        assert_eq!(idx.nt.growable.len(), 1);
+        assert_eq!(idx.find_hex("12")?, Some(0));
+        assert_eq!(idx.find_hex("1a")?, Some(1));
+
+        idx.insert(2, "1a01")?;
+        assert_eq!(idx.nt.growable.len(), 2);
+        assert_eq!(idx.find_hex("1a"), Err(NodeMapError::MultipleResults));
+        assert_eq!(idx.find_hex("12")?, Some(0));
+        assert_eq!(idx.find_hex("1a3")?, Some(1));
+        assert_eq!(idx.find_hex("1a0")?, Some(2));
+        assert_eq!(idx.find_hex("1a12")?, None);
+
+        // now let's make it split and create more than one additional block
+        idx.insert(3, "1a345")?;
+        assert_eq!(idx.nt.growable.len(), 4);
+        assert_eq!(idx.find_hex("1a340")?, Some(1));
+        assert_eq!(idx.find_hex("1a345")?, Some(3));
+        assert_eq!(idx.find_hex("1a341")?, None);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_insert_extreme_splitting() -> Result<(), NodeMapError> {
+        // check that the splitting loop is long enough
+        let mut nt_idx = TestNtIndex::new();
+        let nt = &mut nt_idx.nt;
+        let idx = &mut nt_idx.index;
+
+        let node0_hex = hex_pad_right("444444");
+        let mut node1_hex = hex_pad_right("444444").clone();
+        node1_hex.pop();
+        node1_hex.push('5');
+        let node0 = Node::from_hex(&node0_hex).unwrap();
+        let node1 = Node::from_hex(&node1_hex).unwrap();
+
+        idx.insert(0, node0.clone());
+        nt.insert(idx, &node0, 0)?;
+        idx.insert(1, node1.clone());
+        nt.insert(idx, &node1, 1)?;
+
+        assert_eq!(nt.find_bin(idx, (&node0).into())?, Some(0));
+        assert_eq!(nt.find_bin(idx, (&node1).into())?, Some(1));
+        Ok(())
+    }
+
+    #[test]
+    fn test_insert_partly_immutable() -> Result<(), NodeMapError> {
+        let mut idx = TestNtIndex::new();
+        idx.insert(0, "1234")?;
+        idx.insert(1, "1235")?;
+        idx.insert(2, "131")?;
+        idx.insert(3, "cafe")?;
+        let mut idx = idx.commit();
+        assert_eq!(idx.find_hex("1234")?, Some(0));
+        assert_eq!(idx.find_hex("1235")?, Some(1));
+        assert_eq!(idx.find_hex("131")?, Some(2));
+        assert_eq!(idx.find_hex("cafe")?, Some(3));
+
+        idx.insert(4, "123A")?;
+        assert_eq!(idx.find_hex("1234")?, Some(0));
+        assert_eq!(idx.find_hex("1235")?, Some(1));
+        assert_eq!(idx.find_hex("131")?, Some(2));
+        assert_eq!(idx.find_hex("cafe")?, Some(3));
+        assert_eq!(idx.find_hex("123A")?, Some(4));
+
+        idx.insert(5, "c0")?;
+        assert_eq!(idx.find_hex("cafe")?, Some(3));
+        assert_eq!(idx.find_hex("c0")?, Some(5));
+        assert_eq!(idx.find_hex("c1")?, None);
+        assert_eq!(idx.find_hex("1234")?, Some(0));
+
+        Ok(())
+    }
 }