WIP: sketch out on-disk hextree

Cargo.toml

@@ -19,19 +19,27 @@ Location to value mapping.
 all-features = true
 
 [features]
-default = []
+default = ["disktree"]
+disktree = [
+  "byteorder",
+  "memmap",
+  "serde",
+]
 serde = ["dep:serde"]
 
 [dependencies]
+byteorder = { version = "1", optional = true }
+leb128 = { version = "0.2.5", optional = true }
+memmap = { version = "0.7", optional = true }
 serde = { version = "1", optional = true, features = ["derive"] }
 
 [dev-dependencies]
-byteorder = "1"
+bincode = { version = "1.3.3" }
 criterion = { version = "0.3", features = ["html_reports"] }
 geo = "0.26.0"
-geo-types = "0.7"
 h3o = { version = "0.4.0", features = ["geo"] }
 h3ron = "0.15.1"
+tempfile = "3"
 
 [dev-dependencies.h3-lorawan-regions]
 git = "https://github.com/JayKickliter/h3-lorawan-regions.git"

benches/benches.rs

@@ -1,6 +1,5 @@
 use criterion::{black_box, criterion_group, criterion_main, BenchmarkId, Criterion};
-use geo::polygon;
-use geo_types::coord;
+use geo::{coord, polygon};
 use h3_lorawan_regions::{
     compact::US915 as COMPACT_US915_INDICES, nocompact::US915 as PLAIN_US915_INDICES,
 };
@@ -9,7 +8,7 @@ use h3o::{
     CellIndex, Resolution,
 };
 use h3ron::H3Cell;
-use hextree::{compaction::EqCompactor, Cell, HexTreeMap, HexTreeSet};
+use hextree::{compaction::EqCompactor, disktree::DiskTree, Cell, HexTreeMap, HexTreeSet};
 use std::convert::TryFrom;
 
 fn set_lookup(c: &mut Criterion) {
@@ -49,6 +48,50 @@ fn set_lookup(c: &mut Criterion) {
     }
 }
 
+fn disk_set_lookup(c: &mut Criterion) {
+    let mut group = c.benchmark_group("US915 DiskTreeSet lookup");
+
+    let us915_disk_set = {
+        let us915_set: HexTreeSet = PLAIN_US915_INDICES
+            .iter()
+            .map(|&idx| Cell::try_from(idx).unwrap())
+            .collect();
+        let mut file = tempfile::tempfile().unwrap();
+        us915_set
+            .to_disktree(&mut file, |_, _| Ok::<(), std::io::Error>(()))
+            .unwrap();
+        DiskTree::memmap(file).unwrap()
+    };
+
+    let tarpon_springs = coord! {x: -82.753822, y: 28.15215};
+    let gulf_of_mexico = coord! {x: -83.101920, y: 28.128096};
+    let paris = coord! {x: 2.340340, y: 48.868680};
+
+    for resolution in [0, 4, 8, 12, 15] {
+        let tarpon_springs =
+            Cell::try_from(*H3Cell::from_coordinate(tarpon_springs, resolution).unwrap()).unwrap();
+        let gulf_of_mexico =
+            Cell::try_from(*H3Cell::from_coordinate(gulf_of_mexico, resolution).unwrap()).unwrap();
+        let paris = Cell::try_from(*H3Cell::from_coordinate(paris, resolution).unwrap()).unwrap();
+
+        group.bench_with_input(
+            BenchmarkId::new("Tarpon Spring", resolution),
+            &tarpon_springs,
+            |b, &cell| b.iter(|| us915_disk_set.contains(cell)),
+        );
+
+        group.bench_with_input(
+            BenchmarkId::new("Gulf of Mexico", resolution),
+            &gulf_of_mexico,
+            |b, &cell| b.iter(|| us915_disk_set.contains(cell)),
+        );
+
+        group.bench_with_input(BenchmarkId::new("Paris", resolution), &paris, |b, &cell| {
+            b.iter(|| us915_disk_set.contains(cell))
+        });
+    }
+}
+
 fn set_construction(c: &mut Criterion) {
     let mut group = c.benchmark_group("US915 HexTreeSet construction");
 
@@ -256,8 +299,9 @@ fn subtree_iter(c: &mut Criterion) {
 
 criterion_group!(
     benches,
-    subtree_iter,
     set_lookup,
+    disk_set_lookup,
+    subtree_iter,
     map_lookup,
     set_iteration,
     map_iteration,

src/disktree/dptr.rs

@@ -0,0 +1,82 @@
+use crate::Result;
+use std::{
+    io::{Read, Write},
+    mem::size_of,
+};
+
+/// A 'disk' pointer.
+#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
+#[repr(transparent)]
+pub(crate) struct Dptr(u64);
+
+impl Dptr {
+    #[allow(clippy::cast_possible_truncation)]
+    const MAX: u64 = 2_u64.pow(Self::DISK_REPR_SZ as u32 * 8) - 1;
+    const DISK_REPR_SZ: usize = 5;
+    const NULL: u64 = 0;
+
+    pub(crate) const fn is_null(self) -> bool {
+        self.0 == Self::NULL
+    }
+
+    pub(crate) const fn null() -> Dptr {
+        Dptr(Self::NULL)
+    }
+
+    pub(crate) const fn size() -> u64 {
+        Self::DISK_REPR_SZ as u64
+    }
+
+    /// Read 5 bytes from disk and parses them as litte-endient `u64`.
+    pub(crate) fn read<R>(src: &mut R) -> Result<Self>
+    where
+        R: Read,
+    {
+        let mut buf = [0u8; size_of::<u64>()];
+        src.read_exact(&mut buf[..Self::DISK_REPR_SZ])?;
+        let dptr = u64::from_le_bytes(buf);
+        Ok(dptr.into())
+    }
+
+    /// Read 5 * `n` bytes from disk, for up to n=7, and parses them as
+    /// litte-endien `u64`s.
+    pub(crate) fn read_n<R>(src: &mut R, n: usize) -> Result<Vec<Dptr>>
+    where
+        R: Read,
+    {
+        debug_assert!(n <= 7);
+        let mut buf = [0; Self::DISK_REPR_SZ * 7];
+        src.read_exact(&mut buf[..(Self::DISK_REPR_SZ * n)])?;
+        Ok(buf[..(Self::DISK_REPR_SZ * n)]
+            .chunks(Self::DISK_REPR_SZ)
+            .map(|chunk| {
+                let mut buf = [0u8; size_of::<u64>()];
+                buf[..Self::DISK_REPR_SZ].copy_from_slice(chunk);
+                u64::from_le_bytes(buf)
+            })
+            .map(Dptr)
+            .collect())
+    }
+
+    /// Writes the 5 lower bytes of a `u64` to disk.
+    pub(crate) fn write<W>(self, dst: &mut W) -> Result
+    where
+        W: Write,
+    {
+        let buf = self.0.to_le_bytes();
+        Ok(dst.write_all(&buf[..Self::DISK_REPR_SZ])?)
+    }
+}
+
+impl From<Dptr> for u64 {
+    fn from(Dptr(raw): Dptr) -> u64 {
+        raw
+    }
+}
+
+impl From<u64> for Dptr {
+    fn from(raw: u64) -> Dptr {
+        assert!(raw <= Self::MAX);
+        Dptr(raw)
+    }
+}

src/disktree/iter.rs

@@ -0,0 +1,176 @@
+use crate::{
+    cell::CellStack,
+    disktree::{dptr::Dptr, tree::HDR_SZ, varint},
+    error::Result,
+    Cell,
+};
+use byteorder::ReadBytesExt;
+use std::io::{Cursor, Seek, SeekFrom};
+
+pub(crate) struct Iter<'a> {
+    cell_stack: CellStack,
+    curr_node: Option<(u8, Dptr)>,
+    disktree_buf: &'a [u8],
+    disktree_csr: Cursor<&'a [u8]>,
+    node_stack: Vec<Vec<(u8, Dptr)>>,
+    recycle_bin: Vec<Vec<(u8, Dptr)>>,
+}
+
+enum Node {
+    // File position for the fist byte of value data.
+    Leaf(Dptr),
+    // (H3 Cell digit, file position of child's node tag)
+    Parent(Vec<(u8, Dptr)>),
+}
+
+impl<'a> Iter<'a> {
+    fn seek_to(&mut self, dptr: Dptr) -> Result<Dptr> {
+        Ok(Dptr::from(
+            self.disktree_csr.seek(SeekFrom::Start(u64::from(dptr)))?,
+        ))
+    }
+
+    fn read_base_nodes(rdr: &mut Cursor<&[u8]>) -> Result<Vec<(u8, Dptr)>> {
+        let mut buf = Vec::with_capacity(122);
+        rdr.seek(SeekFrom::Start(HDR_SZ))?;
+        for digit in 0..122 {
+            let dptr = Dptr::read(rdr)?;
+            if !dptr.is_null() {
+                buf.push((digit, dptr));
+            }
+        }
+        buf.reverse();
+        Ok(buf)
+    }
+
+    // `pos` is a position in the file of this node's tag.
+    fn read_node(&mut self, dptr: Dptr) -> Result<Node> {
+        let dptr = self.seek_to(dptr)?;
+        let node_tag = self.disktree_csr.read_u8()?;
+        if 0 == node_tag & 0b1000_0000 {
+            Ok(Node::Leaf(dptr))
+        } else {
+            let mut children = self.node_buf();
+            let n_children = (node_tag & 0b0111_1111).count_ones() as usize;
+            let child_dptrs = Dptr::read_n(&mut self.disktree_csr, n_children)?;
+            children.extend(
+                (0..7)
+                    .rev()
+                    .filter(|digit| node_tag & (1 << digit) != 0)
+                    .zip(child_dptrs.into_iter().rev()),
+            );
+            Ok(Node::Parent(children))
+        }
+    }
+
+    /// Returns a recycled node buffer if available, otherwise
+    /// allocates a new one.
+    ///
+    /// See [`Iter::recycle_node_buf`].
+    fn node_buf(&mut self) -> Vec<(u8, Dptr)> {
+        let buf = self
+            .recycle_bin
+            .pop()
+            .unwrap_or_else(|| Vec::with_capacity(7));
+        debug_assert!(buf.is_empty());
+        buf
+    }
+
+    /// Accepts a used, empty, node buffer for later reuse.
+    ///
+    /// See  [`Iter::node_buf`].
+    fn recycle_node_buf(&mut self, buf: Vec<(u8, Dptr)>) {
+        debug_assert!(buf.is_empty());
+        self.recycle_bin.push(buf);
+    }
+
+    // We've encountered an IO error. We're still going to return
+    // `Some` with the contents of the user's deserializer, but let's
+    // make sure we never yeild another value by clearing stack.
+    fn stop_yeilding(&mut self) {
+        self.node_stack.clear();
+        self.curr_node = None;
+    }
+
+    pub(crate) fn new(disktree_buf: &'a [u8]) -> Result<Iter<'a>> {
+        let mut disktree_csr = Cursor::new(disktree_buf);
+        let mut cell_stack = CellStack::new();
+        let mut node_stack = Vec::new();
+        let recycle_bin = Vec::new();
+        let mut base_nodes = Self::read_base_nodes(&mut disktree_csr)?;
+        let curr_node = base_nodes.pop();
+        node_stack.push(base_nodes);
+        if let Some((digit, _)) = curr_node {
+            cell_stack.push(digit);
+        }
+        Ok(Self {
+            cell_stack,
+            curr_node,
+            disktree_buf,
+            disktree_csr,
+            recycle_bin,
+            node_stack,
+        })
+    }
+}
+
+impl<'a> Iterator for Iter<'a> {
+    type Item = Result<(Cell, &'a [u8])>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while self.curr_node.is_none() {
+            if let Some(mut dptrs) = self.node_stack.pop() {
+                self.cell_stack.pop();
+                if let Some((digit, dptr)) = dptrs.pop() {
+                    self.cell_stack.push(digit);
+                    self.curr_node = Some((digit, dptr));
+                    self.node_stack.push(dptrs);
+                } else {
+                    self.recycle_node_buf(dptrs);
+                }
+            } else {
+                break;
+            }
+        }
+        while let Some((digit, dptr)) = self.curr_node {
+            self.cell_stack.swap(digit);
+            match self.read_node(dptr) {
+                Err(e) => {
+                    self.stop_yeilding();
+                    return Some(Err(e));
+                }
+                Ok(Node::Parent(mut children)) => {
+                    if let Some((digit, dptr)) = children.pop() {
+                        self.cell_stack.push(digit);
+                        self.curr_node = Some((digit, dptr));
+                        self.node_stack.push(children);
+                    } else {
+                        self.recycle_node_buf(children);
+                    }
+                }
+                Ok(Node::Leaf(dptr)) => {
+                    self.curr_node = None;
+                    if let Err(e) = self.seek_to(dptr) {
+                        self.stop_yeilding();
+                        return Some(Err(e));
+                    }
+                    match varint::read(&mut self.disktree_csr) {
+                        Err(e) => {
+                            self.stop_yeilding();
+                            return Some(Err(e));
+                        }
+                        Ok((val_len, _n_read)) => {
+                            let pos = self.disktree_csr.position() as usize;
+                            let val_buf = &self.disktree_buf[pos..][..val_len as usize];
+                            return Some(Ok((
+                                *self.cell_stack.cell().expect("corrupted cell-stack"),
+                                val_buf,
+                            )));
+                        }
+                    }
+                }
+            };
+        }
+        None
+    }
+}