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
// Copyright 2018-2020 Georges Racinet <georges.racinet@octobus.net>
// 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
///
/// 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, 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(())
}
}