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[thin_restore (rust)] rewrite the btree_builder

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Now copes with adding shared leaves.
This commit is contained in:
Joe Thornber 2020-12-09 13:22:32 +00:00
parent 443b3c8f0b
commit 04e0eb3a66
4 changed files with 465 additions and 206 deletions
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524
src/pdata/btree_builder.rs
View File

@ -13,6 +13,56 @@ 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 {
@ -58,100 +108,13 @@ fn pack_node<W: WriteBytesExt, V: Pack + Unpack>(node: &Node<V>, w: &mut W) -> R
Ok(())
}
//------------------------------------------
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
pub struct WriteResult {
first_key: u64,
loc: u64,
}
//------------------------------------------
struct Entries<V> {
pub max_entries: usize,
entries: VecDeque<(u64, V)>,
}
enum Action<V> {
EmitNode(Vec<u64>, Vec<V>), // keys, values
}
use Action::*;
impl<V> Entries<V> {
pub fn new(max_entries: usize) -> Entries<V> {
Entries {
max_entries,
entries: VecDeque::new(),
}
}
pub fn add_entry(&mut self, k: u64, v: V) -> Vec<Action<V>> {
let mut result = Vec::new();
if self.full() {
let (keys, values) = self.pop(self.max_entries);
result.push(EmitNode(keys, values));
}
self.entries.push_back((k, v));
result
}
fn complete_(&mut self, result: &mut Vec<Action<V>>) {
let n = self.entries.len();
if n >= self.max_entries {
let n1 = n / 2;
let n2 = n - n1;
let (keys1, values1) = self.pop(n1);
let (keys2, values2) = self.pop(n2);
result.push(EmitNode(keys1, values1));
result.push(EmitNode(keys2, values2));
} else if n > 0 {
let (keys, values) = self.pop(n);
result.push(EmitNode(keys, values));
}
}
pub fn complete(&mut self) -> Vec<Action<V>> {
let mut result = Vec::new();
self.complete_(&mut result);
result
}
fn full(&self) -> bool {
self.entries.len() >= 2 * self.max_entries
}
fn pop(&mut self, count: usize) -> (Vec<u64>, Vec<V>) {
let mut keys = Vec::new();
let mut values = Vec::new();
for _i in 0..count {
let (k, v) = self.entries.pop_front().unwrap();
keys.push(k);
values.push(v);
}
(keys, values)
}
}
//------------------------------------------
#[allow(dead_code)]
pub struct NodeSummary {
block: u64,
nr_entries: usize,
key_low: u64,
key_high: u64, // inclusive
}
//------------------------------------------
fn write_node_<V: Unpack + Pack>(w: &mut WriteBatcher, mut node: Node<V>) -> Result<(u64, 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();
@ -163,14 +126,25 @@ fn write_node_<V: Unpack + Pack>(w: &mut WriteBatcher, mut node: Node<V>) -> Res
pack_node(&node, &mut cursor)?;
w.write(b, checksum::BT::NODE)?;
Ok((first_key, loc))
Ok(WriteResult { first_key, loc })
}
fn write_leaf<V: Unpack + Pack>(
w: &mut WriteBatcher,
keys: Vec<u64>,
values: Vec<V>,
) -> Result<(u64, u64)> {
/// 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,
@ -186,9 +160,28 @@ fn write_leaf<V: Unpack + Pack>(
};
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)),
}
}
}
fn write_internal(w: &mut WriteBatcher, keys: Vec<u64>, values: Vec<u64>) -> Result<(u64, u64)> {
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,
@ -204,114 +197,309 @@ fn write_internal(w: &mut WriteBatcher, keys: Vec<u64>, values: Vec<u64>) -> Res
};
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");
}
}
}
}
pub struct Builder<V: Unpack + Pack> {
w: WriteBatcher,
entries: Entries<V>,
//------------------------------------------
max_internal_entries: usize,
internal_entries: Vec<Entries<u64>>,
root: u64,
/// 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
}
impl<V: Unpack + Pack> Builder<V> {
//------------------------------------------
/// 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(
engine: Arc<dyn IoEngine + Send + Sync>,
sm: Arc<Mutex<dyn SpaceMap>>,
) -> Builder<V> {
let max_entries = calc_max_entries::<V>();
let max_internal_entries = calc_max_entries::<u64>();
Builder {
w: WriteBatcher::new(engine, sm, 256),
entries: Entries::new(max_entries),
max_internal_entries,
internal_entries: Vec::new(),
root: 0,
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(),
}
}
pub fn add_entry(&mut self, k: u64, v: V) -> Result<()> {
let actions = self.entries.add_entry(k, v);
for a in actions {
self.perform_action(a)?;
/// 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(())
}
pub fn add_leaf_node(&mut self, leaf: &NodeSummary) -> Result<()> {
match leaf.nr_entries {
n if n == 0 => {
// Do nothing
},
n if n < (self.entries.max_entries / 2) => {
// FIXME: what if we've already queued a handful of entries for a node?
// Add the entries individually
todo!();
},
_n => {
let actions = self.entries.complete();
for a in actions {
self.perform_action(a)?;
/// 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");
}
self.add_internal_entry(0, leaf.key_low, leaf.block)?;
}
// 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(())
}
pub fn complete(mut self) -> Result<u64> {
let actions = self.entries.complete();
for a in actions {
self.perform_action(a)?;
}
self.w.flush()?;
Ok(self.root)
/// 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()?;
}
//--------------------
fn add_internal_entry(&mut self, level: usize, k: u64, v: u64) -> Result<()> {
if self.internal_entries.len() == level {
self.internal_entries
.push(Entries::new(self.max_internal_entries));
self.emit_all()?;
Ok(self.nodes)
}
let actions = self.internal_entries[level].add_entry(k, v);
//-------------------------
for a in actions {
self.perform_internal_action(level, a)?;
// 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(())
}
fn perform_internal_action(&mut self, level: usize, action: Action<u64>) -> Result<()> {
match action {
EmitNode(keys, values) => {
let (k, loc) = write_internal(&mut self.w, keys, values)?;
self.add_internal_entry(level + 1, k, loc)?;
self.root = loc;
},
/// 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(())
}
fn perform_action<V2: Unpack + Pack>(&mut self, action: Action<V2>) -> Result<()> {
match action {
EmitNode(keys, values) => {
let (k, loc) = write_leaf(&mut self.w, keys, values)?;
self.add_internal_entry(0, k, loc)?;
},
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)
}
}
//------------------------------------------

17
src/pdata/space_map.rs
View File

@ -2,8 +2,8 @@ use anyhow::{anyhow, Result};
use byteorder::{LittleEndian, WriteBytesExt};
use fixedbitset::FixedBitSet;
use nom::{multi::count, number::complete::*, IResult};
use std::sync::{Arc, Mutex};
use std::boxed::Box;
use std::sync::{Arc, Mutex};
use crate::io_engine::*;
use crate::pdata::unpack::{Pack, Unpack};
@ -226,13 +226,22 @@ pub trait SpaceMap {
fn get_nr_allocated(&self) -> Result<u64>;
fn get(&self, b: u64) -> Result<u32>;
// Returns the old ref count
/// Returns the old ref count
fn set(&mut self, b: u64, v: u32) -> Result<u32>;
fn inc(&mut self, begin: u64, len: u64) -> Result<()>;
// Finds a block with a zero reference count. Increments the
// count.
/// Returns true if the block is now free
fn dec(&mut self, b: u64) -> Result<bool> {
let old = self.get(b)?;
assert!(old > 0);
self.set(b, old - 1)?;
Ok(old == 1)
}
/// Finds a block with a zero reference count. Increments the
/// count.
fn alloc(&mut self) -> Result<Option<u64>>;
}

65
src/thin/restore.rs
View File

@ -1,9 +1,62 @@
use anyhow::Result;
use std::collections::{BTreeMap, BTreeSet};
use std::fs::OpenOptions;
use std::path::Path;
use std::sync::Arc;
use crate::report::*;
use crate::thin::block_time::*;
use crate::thin::device_detail::*;
use crate::thin::superblock::*;
use crate::thin::xml::{self, *};
//------------------------------------------
#[derive(Default)]
struct Pass1 {
//
}
impl MetadataVisitor for Pass1 {
fn superblock_b(&mut self, sb: &xml::Superblock) -> Result<Visit> {
todo!();
}
fn superblock_e(&mut self) -> Result<Visit> {
todo!();
}
fn def_shared_b(&mut self, name: &str) -> Result<Visit> {
todo!();
}
fn def_shared_e(&mut self) -> Result<Visit> {
todo!();
}
fn device_b(&mut self, d: &Device) -> Result<Visit> {
todo!();
}
fn device_e(&mut self) -> Result<Visit> {
todo!();
}
fn map(&mut self, m: &Map) -> Result<Visit> {
todo!();
}
fn ref_shared(&mut self, name: &str) -> Result<Visit> {
todo!();
}
fn eof(&mut self) -> Result<Visit> {
todo!();
}
}
//------------------------------------------
pub struct ThinRestoreOptions<'a> {
@ -15,8 +68,16 @@ pub struct ThinRestoreOptions<'a> {
//------------------------------------------
pub fn restore(_opts: ThinRestoreOptions) -> Result<()> {
todo!();
pub fn restore(opts: ThinRestoreOptions) -> Result<()> {
let input = OpenOptions::new()
.read(true)
.write(false)
.open(opts.input)?;
let mut pass = Pass1::default();
xml::read(input, &mut pass)?;
Ok(())
}
//------------------------------------------

5
src/write_batcher.rs
View File

@ -7,9 +7,10 @@ use crate::pdata::space_map::*;
//------------------------------------------
#[derive(Clone)]
pub struct WriteBatcher {
engine: Arc<dyn IoEngine + Send + Sync>,
sm: Arc<Mutex<dyn SpaceMap>>,
pub engine: Arc<dyn IoEngine + Send + Sync>,
pub sm: Arc<Mutex<dyn SpaceMap>>,
batch_size: usize,
queue: Vec<Block>,