509 lines
15 KiB
Rust
509 lines
15 KiB
Rust
use anyhow::Result;
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use byteorder::{LittleEndian, WriteBytesExt};
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use std::collections::VecDeque;
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use std::io::Cursor;
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use std::sync::{Arc, Mutex};
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use crate::checksum;
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use crate::io_engine::*;
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use crate::pdata::btree::*;
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use crate::pdata::space_map::*;
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use crate::pdata::unpack::*;
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use crate::write_batcher::*;
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//------------------------------------------
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/// A little ref counter abstraction. Used to manage counts for btree
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/// values (eg, the block/time in a thin mapping tree).
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pub trait RefCounter<Value> {
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fn get(&self, v: &Value) -> Result<u32>;
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fn inc(&mut self, v: &Value) -> Result<()>;
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fn dec(&mut self, v: &Value) -> Result<()>;
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}
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pub struct NoopRC {}
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impl<Value> RefCounter<Value> for NoopRC {
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fn get(&self, _v: &Value) -> Result<u32> {Ok(0)}
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fn inc(&mut self, _v: &Value) -> Result<()> {Ok(())}
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fn dec(&mut self, _v: &Value) -> Result<()> {Ok(())}
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}
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/// Wraps a space map up to become a RefCounter.
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struct SMRefCounter {
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sm: Arc<Mutex<dyn SpaceMap>>,
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}
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impl RefCounter<u64> for SMRefCounter {
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fn get(&self, v: &u64) -> Result<u32> {
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self.sm.lock().unwrap().get(*v)
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}
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fn inc(&mut self, v: &u64) -> Result<()> {
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self.sm.lock().unwrap().inc(*v, 1)
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}
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fn dec(&mut self, v: &u64) -> Result<()> {
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self.sm.lock().unwrap().dec(*v)?;
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Ok(())
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}
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}
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//------------------------------------------
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// Building a btree for a given set of values is straight forward.
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// But often we want to merge shared subtrees into the btree we're
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// building, which _is_ complicated. Requiring rebalancing of nodes,
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// and careful copy-on-write operations so we don't disturb the shared
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// subtree.
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//
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// To avoid these problems this code never produces shared internal nodes.
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// With the large fan out of btrees this isn't really a problem; we'll
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// allocate more nodes than optimum, but not many compared to the number
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// of leaves. Also we can pack the leaves much better than the kernel
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// does due to out of order insertions.
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//
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// There are thus two stages to building a btree.
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//
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// i) Produce a list of populated leaves. These leaves may well be shared.
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// ii) Build the upper levels of the btree above the leaves.
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//------------------------------------------
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/// Pack the given node ready to write to disk.
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pub fn pack_node<W: WriteBytesExt, V: Pack + Unpack>(node: &Node<V>, w: &mut W) -> Result<()> {
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match node {
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Node::Internal {
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header,
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keys,
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values,
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} => {
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header.pack(w)?;
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for k in keys {
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w.write_u64::<LittleEndian>(*k)?;
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}
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// pad with zeroes
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for _i in keys.len()..header.max_entries as usize {
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w.write_u64::<LittleEndian>(0)?;
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}
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for v in values {
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v.pack(w)?;
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}
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}
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Node::Leaf {
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header,
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keys,
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values,
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} => {
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header.pack(w)?;
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for k in keys {
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w.write_u64::<LittleEndian>(*k)?;
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}
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// pad with zeroes
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for _i in keys.len()..header.max_entries as usize {
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w.write_u64::<LittleEndian>(0)?;
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}
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for v in values {
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v.pack(w)?;
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}
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}
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}
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Ok(())
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}
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//------------------------------------------
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pub fn calc_max_entries<V: Unpack>() -> usize {
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let elt_size = 8 + V::disk_size() as usize;
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let total = ((BLOCK_SIZE - NodeHeader::disk_size() as usize) / elt_size) as usize;
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total / 3 * 3
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}
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pub struct WriteResult {
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first_key: u64,
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loc: u64,
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}
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/// Write a node to a free metadata block.
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fn write_node_<V: Unpack + Pack>(w: &mut WriteBatcher, mut node: Node<V>) -> Result<WriteResult> {
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let keys = node.get_keys();
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let first_key = keys.first().unwrap_or(&0u64).clone();
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let b = w.alloc()?;
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node.set_block(b.loc);
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let mut cursor = Cursor::new(b.get_data());
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pack_node(&node, &mut cursor)?;
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let loc = b.loc;
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w.write(b, checksum::BT::NODE)?;
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Ok(WriteResult { first_key, loc })
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}
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/// A node writer takes a Vec of values and packs them into
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/// a btree node. It's up to the specific implementation to
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/// decide if it produces internal or leaf nodes.
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pub trait NodeIO<V: Unpack + Pack> {
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fn write(&self, w: &mut WriteBatcher, keys: Vec<u64>, values: Vec<V>) -> Result<WriteResult>;
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fn read(
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&self,
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engine: &Arc<dyn IoEngine + Send + Sync>,
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block: u64,
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) -> Result<(Vec<u64>, Vec<V>)>;
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}
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pub struct LeafIO {}
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impl<V: Unpack + Pack> NodeIO<V> for LeafIO {
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fn write(&self, w: &mut WriteBatcher, keys: Vec<u64>, values: Vec<V>) -> Result<WriteResult> {
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let header = NodeHeader {
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block: 0,
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is_leaf: true,
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nr_entries: keys.len() as u32,
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max_entries: calc_max_entries::<V>() as u32,
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value_size: V::disk_size(),
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};
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let node = Node::Leaf {
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header,
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keys,
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values,
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};
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write_node_(w, node)
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}
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fn read(
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&self,
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engine: &Arc<dyn IoEngine + Send + Sync>,
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block: u64,
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) -> Result<(Vec<u64>, Vec<V>)> {
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let b = engine.read(block)?;
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let path = Vec::new();
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match unpack_node::<V>(&path, b.get_data(), true, true)? {
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Node::Internal { .. } => {
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panic!("unexpected internal node");
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}
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Node::Leaf { keys, values, .. } => Ok((keys, values)),
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}
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}
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}
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struct InternalIO {}
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impl NodeIO<u64> for InternalIO {
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fn write(&self, w: &mut WriteBatcher, keys: Vec<u64>, values: Vec<u64>) -> Result<WriteResult> {
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let header = NodeHeader {
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block: 0,
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is_leaf: false,
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nr_entries: keys.len() as u32,
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max_entries: calc_max_entries::<u64>() as u32,
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value_size: u64::disk_size(),
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};
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let node: Node<u64> = Node::Internal {
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header,
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keys,
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values,
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};
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write_node_(w, node)
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}
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fn read(
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&self,
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engine: &Arc<dyn IoEngine + Send + Sync>,
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block: u64,
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) -> Result<(Vec<u64>, Vec<u64>)> {
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let b = engine.read(block)?;
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let path = Vec::new();
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match unpack_node::<u64>(&path, b.get_data(), true, true)? {
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Node::Internal { keys, values, .. } => Ok((keys, values)),
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Node::Leaf { .. } => {
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panic!("unexpected leaf node");
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}
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}
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}
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}
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//------------------------------------------
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/// This takes a sequence of values or nodes, and builds a vector of leaf nodes.
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/// Care is taken to make sure that all nodes are at least half full unless there's
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/// only a single node.
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pub struct NodeBuilder<V: Pack + Unpack> {
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nio: Box<dyn NodeIO<V>>,
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value_rc: Box<dyn RefCounter<V>>,
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max_entries_per_node: usize,
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values: VecDeque<(u64, V)>,
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nodes: Vec<NodeSummary>,
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}
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/// When the builder is including pre-built nodes it has to decide whether
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/// to use the node as given, or read it and import the values directly
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/// for balancing reasons. This struct is used to stop us re-reading
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/// the NodeHeaders of nodes that are shared multiple times.
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#[derive(Clone)]
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pub struct NodeSummary {
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block: u64,
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key: u64,
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nr_entries: usize,
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/// This node was passed in pre-built. Important for deciding if
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/// we need to adjust the ref counts if we unpack.
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shared: bool,
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}
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impl<'a, V: Pack + Unpack + Clone> NodeBuilder<V> {
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/// Create a new NodeBuilder
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pub fn new(
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nio: Box<dyn NodeIO<V>>,
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value_rc: Box<dyn RefCounter<V>>,
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) -> Self {
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NodeBuilder {
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nio,
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value_rc,
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max_entries_per_node: calc_max_entries::<V>(),
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values: VecDeque::new(),
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nodes: Vec::new(),
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}
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}
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/// Push a single value. This may emit a new node, hence the Result
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/// return type. The value's ref count will be incremented.
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pub fn push_value(&mut self, w: &mut WriteBatcher, key: u64, val: V) -> Result<()> {
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// Have we got enough values to emit a node? We try and keep
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// at least max_entries_per_node entries unflushed so we
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// can ensure the final node is balanced properly.
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if self.values.len() == self.max_entries_per_node * 2 {
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self.emit_node(w)?;
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}
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self.value_rc.inc(&val)?;
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self.values.push_back((key, val));
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Ok(())
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}
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/// Push a number of prebuilt, shared nodes. The builder may decide to not
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/// use a shared node, instead reading the values and packing them
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/// directly. This may do IO to emit nodes, so returns a Result.
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/// Any shared nodes that are used have their block incremented in
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/// the space map. Will only increment the ref count for values
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/// contained in the nodes if it unpacks them.
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pub fn push_nodes(&mut self, w: &mut WriteBatcher, nodes: &Vec<NodeSummary>) -> Result<()> {
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assert!(nodes.len() > 0);
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// As a sanity check we make sure that all the shared nodes contain the
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// minimum nr of entries.
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let half_full = self.max_entries_per_node / 2;
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for n in nodes {
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if n.nr_entries < half_full {
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panic!("under populated node");
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}
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}
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// Decide if we're going to use the pre-built nodes.
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if self.values.len() < half_full {
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// To avoid writing an under populated node we have to grab some
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// values from the first of the shared nodes.
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let (keys, values) = self.read_node(w, nodes.get(0).unwrap().block)?;
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for i in 0..keys.len() {
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self.value_rc.inc(&values[i])?;
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self.values.push_back((keys[i], values[i].clone()));
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}
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// Flush all the values.
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self.emit_all(w)?;
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// Add the remaining nodes.
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for i in 1..nodes.len() {
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let n = nodes.get(i).unwrap();
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w.sm.lock().unwrap().inc(n.block, 1)?;
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self.nodes.push(n.clone());
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}
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} else {
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// Flush all the values.
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self.emit_all(w)?;
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// add the nodes
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for n in nodes {
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w.sm.lock().unwrap().inc(n.block, 1)?;
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self.nodes.push(n.clone());
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}
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}
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Ok(())
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}
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/// Signal that no more values or nodes will be pushed. Returns a
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/// vector of the built nodes. Consumes the builder.
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pub fn complete(mut self, w: &mut WriteBatcher) -> Result<Vec<NodeSummary>> {
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let half_full = self.max_entries_per_node / 2;
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if (self.nodes.len() > 0) && (self.values.len() < half_full) {
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// We don't have enough values to emit a node. So we're going to
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// have to rebalance with the previous node.
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self.unshift_node(w)?;
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}
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self.emit_all(w)?;
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if self.nodes.len() == 0 {
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self.emit_empty_leaf(w)?
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}
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Ok(self.nodes)
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}
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//-------------------------
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// We're only interested in the keys and values from the node, and
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// not whether it's a leaf or internal node.
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fn read_node(&self, w: &WriteBatcher, block: u64) -> Result<(Vec<u64>, Vec<V>)> {
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self.nio.read(&w.engine, block)
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}
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/// Writes a node with the first 'nr_entries' values.
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fn emit_values(&mut self, w: &mut WriteBatcher, nr_entries: usize) -> Result<()> {
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assert!(nr_entries <= self.values.len());
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// Write the node
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let mut keys = Vec::new();
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let mut values = Vec::new();
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for _i in 0..nr_entries {
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let (k, v) = self.values.pop_front().unwrap();
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keys.push(k);
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values.push(v);
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}
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let wresult = self.nio.write(w, keys, values)?;
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// Push a summary to the 'nodes' vector.
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self.nodes.push(NodeSummary {
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block: wresult.loc,
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key: wresult.first_key,
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nr_entries,
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shared: false,
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});
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Ok(())
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}
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/// Writes a full node.
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fn emit_node(&mut self, w: &mut WriteBatcher) -> Result<()> {
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self.emit_values(w, self.max_entries_per_node)
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}
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/// Emits all remaining values. Panics if there are more than 2 *
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/// max_entries_per_node values.
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fn emit_all(&mut self, w: &mut WriteBatcher) -> Result<()> {
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match self.values.len() {
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0 => {
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// There's nothing to emit
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Ok(())
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}
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n if n <= self.max_entries_per_node => {
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// Emit a single node.
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self.emit_values(w, n)
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}
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n if n <= self.max_entries_per_node * 2 => {
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// Emit two nodes.
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let n1 = n / 2;
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let n2 = n - n1;
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self.emit_values(w, n1)?;
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self.emit_values(w, n2)
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}
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_ => {
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panic!("self.values shouldn't have more than 2 * max_entries_per_node entries");
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}
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}
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}
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fn emit_empty_leaf(&mut self, w: &mut WriteBatcher) -> Result<()> {
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self.emit_values(w, 0)
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}
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/// Pops the last node, and prepends it's values to 'self.values'. Used
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/// to rebalance when we have insufficient values for a final node. The
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/// node is decremented in the space map.
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fn unshift_node(&mut self, w: &mut WriteBatcher) -> Result<()> {
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let ls = self.nodes.pop().unwrap();
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let (keys, values) = self.read_node(w, ls.block)?;
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w.sm.lock().unwrap().dec(ls.block)?;
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let mut vals = VecDeque::new();
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for i in 0..keys.len() {
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// We only need to inc the values if the node was pre built.
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if ls.shared {
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self.value_rc.inc(&values[i])?;
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}
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vals.push_back((keys[i], values[i].clone()));
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}
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vals.append(&mut self.values);
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std::mem::swap(&mut self.values, &mut vals);
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Ok(())
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}
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}
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//------------------------------------------
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pub struct Builder<V: Unpack + Pack> {
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leaf_builder: NodeBuilder<V>,
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}
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impl<V: Unpack + Pack + Clone> Builder<V> {
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pub fn new(
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value_rc: Box<dyn RefCounter<V>>,
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) -> Builder<V> {
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Builder {
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leaf_builder: NodeBuilder::new(
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Box::new(LeafIO {}),
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value_rc,
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),
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}
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}
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pub fn push_value(&mut self, w: &mut WriteBatcher, k: u64, v: V) -> Result<()> {
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self.leaf_builder.push_value(w, k, v)
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}
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pub fn push_leaves(&mut self, w: &mut WriteBatcher, leaves: &Vec<NodeSummary>) -> Result<()> {
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self.leaf_builder.push_nodes(w, leaves)
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}
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pub fn complete(self, w: &mut WriteBatcher) -> Result<u64> {
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let mut nodes = self.leaf_builder.complete(w)?;
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// Now we iterate, adding layers of internal nodes until we end
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// up with a single root.
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while nodes.len() > 1 {
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let mut builder = NodeBuilder::new(
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Box::new(InternalIO {}),
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Box::new(SMRefCounter {
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sm: w.sm.clone(),
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}),
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);
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for n in nodes {
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builder.push_value(w, n.key, n.block)?;
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}
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nodes = builder.complete(w)?;
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}
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assert!(nodes.len() == 1);
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Ok(nodes[0].block)
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}
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}
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//------------------------------------------
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