506 lines
15 KiB
Rust
506 lines
15 KiB
Rust
use anyhow::Result;
|
|
use byteorder::{LittleEndian, WriteBytesExt};
|
|
use std::collections::VecDeque;
|
|
use std::io::Cursor;
|
|
use std::sync::{Arc, Mutex};
|
|
|
|
use crate::checksum;
|
|
use crate::io_engine::*;
|
|
use crate::pdata::btree::*;
|
|
use crate::pdata::space_map::*;
|
|
use crate::pdata::unpack::*;
|
|
use crate::write_batcher::*;
|
|
|
|
//------------------------------------------
|
|
|
|
/// A little ref counter abstraction. Used to manage counts for btree
|
|
/// values (eg, the block/time in a thin mapping tree).
|
|
pub trait RefCounter<Value> {
|
|
fn get(&self, v: &Value) -> Result<u32>;
|
|
fn inc(&mut self, v: &Value) -> Result<()>;
|
|
fn dec(&mut self, v: &Value) -> Result<()>;
|
|
}
|
|
|
|
/// Wraps a space map up to become a RefCounter.
|
|
struct SMRefCounter {
|
|
sm: Arc<Mutex<dyn SpaceMap>>,
|
|
}
|
|
|
|
impl RefCounter<u64> for SMRefCounter {
|
|
fn get(&self, v: &u64) -> Result<u32> {
|
|
self.sm.lock().unwrap().get(*v)
|
|
}
|
|
|
|
fn inc(&mut self, v: &u64) -> Result<()> {
|
|
self.sm.lock().unwrap().inc(*v, 1)
|
|
}
|
|
|
|
fn dec(&mut self, v: &u64) -> Result<()> {
|
|
self.sm.lock().unwrap().dec(*v)?;
|
|
Ok(())
|
|
}
|
|
}
|
|
|
|
//------------------------------------------
|
|
|
|
// Building a btree for a given set of values is straight forward.
|
|
// But often we want to merge shared subtrees into the btree we're
|
|
// building, which _is_ complicated. Requiring rebalancing of nodes,
|
|
// and careful copy-on-write operations so we don't disturb the shared
|
|
// subtree.
|
|
//
|
|
// To avoid these problems this code never produces shared internal nodes.
|
|
// With the large fan out of btrees this isn't really a problem; we'll
|
|
// allocate more nodes than optimum, but not many compared to the number
|
|
// of leaves. Also we can pack the leaves much better than the kernel
|
|
// does due to out of order insertions.
|
|
//
|
|
// There are thus two stages to building a btree.
|
|
//
|
|
// i) Produce a list of populated leaves. These leaves may well be shared.
|
|
// ii) Build the upper levels of the btree above the leaves.
|
|
|
|
//------------------------------------------
|
|
|
|
/// Pack the given node ready to write to disk.
|
|
fn pack_node<W: WriteBytesExt, V: Pack + Unpack>(node: &Node<V>, w: &mut W) -> Result<()> {
|
|
match node {
|
|
Node::Internal {
|
|
header,
|
|
keys,
|
|
values,
|
|
} => {
|
|
header.pack(w)?;
|
|
for k in keys {
|
|
w.write_u64::<LittleEndian>(*k)?;
|
|
}
|
|
|
|
// pad with zeroes
|
|
for _i in keys.len()..header.max_entries as usize {
|
|
w.write_u64::<LittleEndian>(0)?;
|
|
}
|
|
|
|
for v in values {
|
|
v.pack(w)?;
|
|
}
|
|
}
|
|
Node::Leaf {
|
|
header,
|
|
keys,
|
|
values,
|
|
} => {
|
|
header.pack(w)?;
|
|
for k in keys {
|
|
w.write_u64::<LittleEndian>(*k)?;
|
|
}
|
|
|
|
// pad with zeroes
|
|
for _i in keys.len()..header.max_entries as usize {
|
|
w.write_u64::<LittleEndian>(0)?;
|
|
}
|
|
|
|
for v in values {
|
|
v.pack(w)?;
|
|
}
|
|
}
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
|
|
pub struct WriteResult {
|
|
first_key: u64,
|
|
loc: u64,
|
|
}
|
|
|
|
/// Write a node to a free metadata block.
|
|
fn write_node_<V: Unpack + Pack>(w: &mut WriteBatcher, mut node: Node<V>) -> Result<WriteResult> {
|
|
let keys = node.get_keys();
|
|
let first_key = keys.first().unwrap_or(&0u64).clone();
|
|
|
|
let loc = w.alloc()?;
|
|
node.set_block(loc);
|
|
|
|
let b = Block::new(loc);
|
|
let mut cursor = Cursor::new(b.get_data());
|
|
pack_node(&node, &mut cursor)?;
|
|
w.write(b, checksum::BT::NODE)?;
|
|
|
|
Ok(WriteResult { first_key, loc })
|
|
}
|
|
|
|
/// A node writer takes a Vec of values and packs them into
|
|
/// a btree node. It's up to the specific implementation to
|
|
/// decide if it produces internal or leaf nodes.
|
|
pub trait NodeIO<V: Unpack + Pack> {
|
|
fn write(&self, w: &mut WriteBatcher, keys: Vec<u64>, values: Vec<V>) -> Result<WriteResult>;
|
|
fn read(
|
|
&self,
|
|
engine: &Arc<dyn IoEngine + Send + Sync>,
|
|
block: u64,
|
|
) -> Result<(Vec<u64>, Vec<V>)>;
|
|
}
|
|
|
|
struct LeafIO {}
|
|
|
|
impl<V: Unpack + Pack> NodeIO<V> for LeafIO {
|
|
fn write(&self, w: &mut WriteBatcher, keys: Vec<u64>, values: Vec<V>) -> Result<WriteResult> {
|
|
let header = NodeHeader {
|
|
block: 0,
|
|
is_leaf: true,
|
|
nr_entries: keys.len() as u32,
|
|
max_entries: calc_max_entries::<V>() as u32,
|
|
value_size: V::disk_size(),
|
|
};
|
|
|
|
let node = Node::Leaf {
|
|
header,
|
|
keys,
|
|
values,
|
|
};
|
|
|
|
write_node_(w, node)
|
|
}
|
|
|
|
fn read(
|
|
&self,
|
|
engine: &Arc<dyn IoEngine + Send + Sync>,
|
|
block: u64,
|
|
) -> Result<(Vec<u64>, Vec<V>)> {
|
|
let b = engine.read(block)?;
|
|
let path = Vec::new();
|
|
match unpack_node::<V>(&path, b.get_data(), true, true)? {
|
|
Node::Internal { .. } => {
|
|
panic!("unexpected internal node");
|
|
}
|
|
Node::Leaf { keys, values, .. } => Ok((keys, values)),
|
|
}
|
|
}
|
|
}
|
|
|
|
struct InternalIO {}
|
|
|
|
impl NodeIO<u64> for InternalIO {
|
|
fn write(&self, w: &mut WriteBatcher, keys: Vec<u64>, values: Vec<u64>) -> Result<WriteResult> {
|
|
let header = NodeHeader {
|
|
block: 0,
|
|
is_leaf: false,
|
|
nr_entries: keys.len() as u32,
|
|
max_entries: calc_max_entries::<u64>() as u32,
|
|
value_size: u64::disk_size(),
|
|
};
|
|
|
|
let node: Node<u64> = Node::Internal {
|
|
header,
|
|
keys,
|
|
values,
|
|
};
|
|
|
|
write_node_(w, node)
|
|
}
|
|
|
|
fn read(
|
|
&self,
|
|
engine: &Arc<dyn IoEngine + Send + Sync>,
|
|
block: u64,
|
|
) -> Result<(Vec<u64>, Vec<u64>)> {
|
|
let b = engine.read(block)?;
|
|
let path = Vec::new();
|
|
match unpack_node::<u64>(&path, b.get_data(), true, true)? {
|
|
Node::Internal { keys, values, .. } => Ok((keys, values)),
|
|
Node::Leaf { .. } => {
|
|
panic!("unexpected leaf node");
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
//------------------------------------------
|
|
|
|
/// What is the maximum number of entries of a given size we can fit in
|
|
/// a btree node?
|
|
fn calc_max_entries<V: Unpack>() -> usize {
|
|
let elt_size = 8 + V::disk_size() as usize;
|
|
((BLOCK_SIZE - NodeHeader::disk_size() as usize) / elt_size) as usize
|
|
}
|
|
|
|
//------------------------------------------
|
|
|
|
/// This takes a sequence of values or nodes, and builds a vector of leaf nodes.
|
|
/// Care is taken to make sure that all nodes are at least half full unless there's
|
|
/// only a single node.
|
|
pub struct NodeBuilder<V: Pack + Unpack> {
|
|
batcher: WriteBatcher,
|
|
nio: Box<dyn NodeIO<V>>,
|
|
value_rc: Box<dyn RefCounter<V>>,
|
|
max_entries_per_node: usize,
|
|
values: VecDeque<(u64, V)>,
|
|
nodes: Vec<NodeSummary>,
|
|
}
|
|
|
|
/// When the builder is including pre-built nodes it has to decide whether
|
|
/// to use the node as given, or read it and import the values directly
|
|
/// for balancing reasons. This struct is used to stop us re-reading
|
|
/// the NodeHeaders of nodes that are shared multiple times.
|
|
#[derive(Clone)]
|
|
pub struct NodeSummary {
|
|
block: u64,
|
|
key: u64,
|
|
nr_entries: usize,
|
|
|
|
/// This node was passed in pre-built. Important for deciding if
|
|
/// we need to adjust the ref counts if we unpack.
|
|
shared: bool,
|
|
}
|
|
|
|
impl<V: Pack + Unpack + Clone> NodeBuilder<V> {
|
|
/// Create a new NodeBuilder
|
|
pub fn new(
|
|
batcher: WriteBatcher,
|
|
nio: Box<dyn NodeIO<V>>,
|
|
value_rc: Box<dyn RefCounter<V>>,
|
|
) -> Self {
|
|
NodeBuilder {
|
|
batcher,
|
|
nio,
|
|
value_rc,
|
|
max_entries_per_node: calc_max_entries::<V>(),
|
|
values: VecDeque::new(),
|
|
nodes: Vec::new(),
|
|
}
|
|
}
|
|
|
|
/// Push a single value. This may emit a new node, hence the Result
|
|
/// return type. The value's ref count will be incremented.
|
|
pub fn push_value(&mut self, key: u64, val: V) -> Result<()> {
|
|
// Have we got enough values to emit a node? We try and keep
|
|
// at least max_entries_per_node entries unflushed so we
|
|
// can ensure the final node is balanced properly.
|
|
if self.values.len() == self.max_entries_per_node * 2 {
|
|
self.emit_node()?;
|
|
}
|
|
|
|
self.value_rc.inc(&val)?;
|
|
self.values.push_back((key, val));
|
|
Ok(())
|
|
}
|
|
|
|
/// Push a number of prebuilt, shared nodes. The builder may decide to not
|
|
/// use a shared node, instead reading the values and packing them
|
|
/// directly. This may do IO to emit nodes, so returns a Result.
|
|
/// Any shared nodes that are used have their block incremented in
|
|
/// the space map. Will only increment the ref count for values
|
|
/// contained in the nodes if it unpacks them.
|
|
pub fn push_nodes(&mut self, nodes: &Vec<NodeSummary>) -> Result<()> {
|
|
assert!(nodes.len() > 0);
|
|
|
|
// As a sanity check we make sure that all the shared nodes contain the
|
|
// minimum nr of entries.
|
|
let half_full = self.max_entries_per_node / 2;
|
|
for n in nodes {
|
|
if n.nr_entries < half_full {
|
|
panic!("under populated node");
|
|
}
|
|
}
|
|
|
|
// Decide if we're going to use the pre-built nodes.
|
|
if self.values.len() < half_full {
|
|
// To avoid writing an under populated node we have to grab some
|
|
// values from the first of the shared nodes.
|
|
let (keys, values) = self.read_node(nodes.get(0).unwrap().block)?;
|
|
|
|
for i in 0..keys.len() {
|
|
self.value_rc.inc(&values[i])?;
|
|
self.values.push_back((keys[i], values[i].clone()));
|
|
}
|
|
|
|
// Flush all the values.
|
|
self.emit_all()?;
|
|
|
|
// Add the remaining nodes.
|
|
for i in 1..nodes.len() {
|
|
let n = nodes.get(i).unwrap();
|
|
self.batcher.sm.lock().unwrap().inc(n.block, 1)?;
|
|
self.nodes.push(n.clone());
|
|
}
|
|
} else {
|
|
// Flush all the values.
|
|
self.emit_all()?;
|
|
|
|
// add the nodes
|
|
for n in nodes {
|
|
self.batcher.sm.lock().unwrap().inc(n.block, 1)?;
|
|
self.nodes.push(n.clone());
|
|
}
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
|
|
/// Signal that no more values or nodes will be pushed. Returns a
|
|
/// vector of the built nodes. Consumes the builder.
|
|
pub fn complete(mut self) -> Result<Vec<NodeSummary>> {
|
|
let half_full = self.max_entries_per_node / 2;
|
|
|
|
if (self.nodes.len() > 0) && (self.values.len() < half_full) {
|
|
// We don't have enough values to emit a node. So we're going to
|
|
// have to rebalance with the previous node.
|
|
self.unshift_node()?;
|
|
}
|
|
|
|
self.emit_all()?;
|
|
Ok(self.nodes)
|
|
}
|
|
|
|
//-------------------------
|
|
|
|
// We're only interested in the keys and values from the node, and
|
|
// not whether it's a leaf or internal node.
|
|
fn read_node(&self, block: u64) -> Result<(Vec<u64>, Vec<V>)> {
|
|
self.nio.read(&self.batcher.engine, block)
|
|
}
|
|
|
|
/// Writes a node with the first 'nr_entries' values.
|
|
fn emit_values(&mut self, nr_entries: usize) -> Result<()> {
|
|
assert!(self.values.len() <= nr_entries);
|
|
|
|
// Write the node
|
|
let mut keys = Vec::new();
|
|
let mut values = Vec::new();
|
|
|
|
for _i in 0..nr_entries {
|
|
let (k, v) = self.values.pop_front().unwrap();
|
|
keys.push(k);
|
|
values.push(v);
|
|
}
|
|
|
|
let wresult = self.nio.write(&mut self.batcher, keys, values)?;
|
|
|
|
// Push a summary to the 'nodes' vector.
|
|
self.nodes.push(NodeSummary {
|
|
block: wresult.loc,
|
|
key: wresult.first_key,
|
|
nr_entries,
|
|
shared: false,
|
|
});
|
|
Ok(())
|
|
}
|
|
|
|
/// Writes a full node.
|
|
fn emit_node(&mut self) -> Result<()> {
|
|
self.emit_values(self.max_entries_per_node)
|
|
}
|
|
|
|
/// Emits all remaining values. Panics if there are more than 2 *
|
|
/// max_entries_per_node values.
|
|
fn emit_all(&mut self) -> Result<()> {
|
|
match self.values.len() {
|
|
0 => {
|
|
// There's nothing to emit
|
|
Ok(())
|
|
}
|
|
n if n <= self.max_entries_per_node => {
|
|
// Emit a single node.
|
|
self.emit_values(n)
|
|
}
|
|
n if n <= self.max_entries_per_node * 2 => {
|
|
// Emit two nodes.
|
|
let n1 = n / 2;
|
|
let n2 = n - n1;
|
|
self.emit_values(n1)?;
|
|
self.emit_values(n2)
|
|
}
|
|
_ => {
|
|
panic!("self.values shouldn't have more than 2 * max_entries_per_node entries");
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Pops the last node, and prepends it's values to 'self.values'. Used
|
|
/// to rebalance when we have insufficient values for a final node. The
|
|
/// node is decremented in the space map.
|
|
fn unshift_node(&mut self) -> Result<()> {
|
|
let ls = self.nodes.pop().unwrap();
|
|
let (keys, values) = self.read_node(ls.block)?;
|
|
self.batcher.sm.lock().unwrap().dec(ls.block)?;
|
|
|
|
let mut vals = VecDeque::new();
|
|
|
|
for i in 0..keys.len() {
|
|
// We only need to inc the values if the node was pre built.
|
|
if ls.shared {
|
|
self.value_rc.inc(&values[i])?;
|
|
}
|
|
vals.push_back((keys[i], values[i].clone()));
|
|
}
|
|
|
|
vals.append(&mut self.values);
|
|
std::mem::swap(&mut self.values, &mut vals);
|
|
|
|
Ok(())
|
|
}
|
|
}
|
|
|
|
//------------------------------------------
|
|
|
|
pub struct Builder<V: Unpack + Pack> {
|
|
engine: Arc<dyn IoEngine + Send + Sync>,
|
|
sm: Arc<Mutex<dyn SpaceMap>>,
|
|
leaf_builder: NodeBuilder<V>,
|
|
}
|
|
|
|
const BATCH_SIZE: usize = 128;
|
|
|
|
impl<V: Unpack + Pack + Clone> Builder<V> {
|
|
pub fn new(
|
|
engine: Arc<dyn IoEngine + Send + Sync>,
|
|
sm: Arc<Mutex<dyn SpaceMap>>,
|
|
value_rc: Box<dyn RefCounter<V>>,
|
|
) -> Builder<V> {
|
|
Builder {
|
|
engine: engine.clone(),
|
|
sm: sm.clone(),
|
|
leaf_builder: NodeBuilder::new(
|
|
WriteBatcher::new(engine.clone(), sm.clone(), BATCH_SIZE),
|
|
Box::new(LeafIO {}),
|
|
value_rc,
|
|
),
|
|
}
|
|
}
|
|
|
|
pub fn push_value(&mut self, k: u64, v: V) -> Result<()> {
|
|
self.leaf_builder.push_value(k, v)
|
|
}
|
|
|
|
pub fn push_leaves(&mut self, leaves: &Vec<NodeSummary>) -> Result<()> {
|
|
self.leaf_builder.push_nodes(leaves)
|
|
}
|
|
|
|
pub fn complete(self) -> Result<u64> {
|
|
let mut nodes = self.leaf_builder.complete()?;
|
|
|
|
// Now we iterate, adding layers of internal nodes until we end
|
|
// up with a single root.
|
|
while nodes.len() > 1 {
|
|
let mut builder = NodeBuilder::new(
|
|
WriteBatcher::new(self.engine.clone(), self.sm.clone(), BATCH_SIZE),
|
|
Box::new(InternalIO {}),
|
|
Box::new(SMRefCounter {
|
|
sm: self.sm.clone(),
|
|
}),
|
|
);
|
|
|
|
for n in nodes {
|
|
builder.push_value(n.key, n.block)?;
|
|
}
|
|
|
|
nodes = builder.complete()?;
|
|
}
|
|
|
|
assert!(nodes.len() == 1);
|
|
Ok(nodes[0].block)
|
|
}
|
|
}
|
|
|
|
//------------------------------------------
|