differential_dataflow/trace/implementations/rhh.rs
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//! Batch implementation based on Robin Hood Hashing.
//!
//! Items are ordered by `(hash(Key), Key)` rather than `Key`, which means
//! that these implementations should only be used with each other, under
//! the same `hash` function, or for types that also order by `(hash(X), X)`,
//! for example wrapped types that implement `Ord` that way.
use std::rc::Rc;
use std::cmp::Ordering;
use serde::{Deserialize, Serialize};
use timely::container::columnation::TimelyStack;
use crate::Hashable;
use crate::trace::implementations::chunker::{ColumnationChunker, VecChunker};
use crate::trace::implementations::merge_batcher::{MergeBatcher, VecMerger};
use crate::trace::implementations::merge_batcher_col::ColumnationMerger;
use crate::trace::implementations::spine_fueled::Spine;
use crate::trace::rc_blanket_impls::RcBuilder;
use super::{Update, Layout, Vector, TStack};
use self::val_batch::{RhhValBatch, RhhValBuilder};
/// A trace implementation using a spine of ordered lists.
pub type VecSpine<K, V, T, R> = Spine<
Rc<RhhValBatch<Vector<((K,V),T,R)>>>,
MergeBatcher<Vec<((K,V),T,R)>, VecChunker<((K,V),T,R)>, VecMerger<((K, V), T, R)>, T>,
RcBuilder<RhhValBuilder<Vector<((K,V),T,R)>, Vec<((K,V),T,R)>>>,
>;
// /// A trace implementation for empty values using a spine of ordered lists.
// pub type OrdKeySpine<K, T, R> = Spine<Rc<OrdKeyBatch<Vector<((K,()),T,R)>>>>;
/// A trace implementation backed by columnar storage.
pub type ColSpine<K, V, T, R> = Spine<
Rc<RhhValBatch<TStack<((K,V),T,R)>>>,
MergeBatcher<Vec<((K,V),T,R)>, ColumnationChunker<((K,V),T,R)>, ColumnationMerger<((K,V),T,R)>, T>,
RcBuilder<RhhValBuilder<TStack<((K,V),T,R)>, TimelyStack<((K,V),T,R)>>>,
>;
// /// A trace implementation backed by columnar storage.
// pub type ColKeySpine<K, T, R> = Spine<Rc<OrdKeyBatch<TStack<((K,()),T,R)>>>>;
/// A carrier trait indicating that the type's `Ord` and `PartialOrd` implementations are by `Hashable::hashed()`.
pub trait HashOrdered: Hashable { }
impl<'a, T: std::hash::Hash + HashOrdered> HashOrdered for &'a T { }
/// A hash-ordered wrapper that modifies `Ord` and `PartialOrd`.
#[derive(Copy, Clone, Eq, PartialEq, Debug, Default, Serialize, Deserialize)]
pub struct HashWrapper<T: std::hash::Hash + Hashable> {
/// The inner value, freely modifiable.
pub inner: T
}
impl<T: PartialOrd + std::hash::Hash + Hashable> PartialOrd for HashWrapper<T>
where <T as Hashable>::Output: PartialOrd {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
let this_hash = self.inner.hashed();
let that_hash = other.inner.hashed();
(this_hash, &self.inner).partial_cmp(&(that_hash, &other.inner))
}
}
impl<T: Ord + PartialOrd + std::hash::Hash + Hashable> Ord for HashWrapper<T>
where <T as Hashable>::Output: PartialOrd {
fn cmp(&self, other: &Self) -> Ordering {
self.partial_cmp(other).unwrap()
}
}
impl<T: std::hash::Hash + Hashable> HashOrdered for HashWrapper<T> { }
impl<T: std::hash::Hash + Hashable> Hashable for HashWrapper<T> {
type Output = T::Output;
fn hashed(&self) -> Self::Output { self.inner.hashed() }
}
impl<T: std::hash::Hash + Hashable> HashOrdered for &HashWrapper<T> { }
impl<T: std::hash::Hash + Hashable> Hashable for &HashWrapper<T> {
type Output = T::Output;
fn hashed(&self) -> Self::Output { self.inner.hashed() }
}
mod val_batch {
use std::convert::TryInto;
use std::marker::PhantomData;
use serde::{Deserialize, Serialize};
use timely::container::PushInto;
use timely::progress::{Antichain, frontier::AntichainRef};
use crate::hashable::Hashable;
use crate::trace::{Batch, BatchReader, Builder, Cursor, Description, Merger};
use crate::trace::implementations::{BatchContainer, BuilderInput};
use crate::trace::cursor::IntoOwned;
use super::{Layout, Update, HashOrdered};
/// Update tuples organized as a Robin Hood Hash map, ordered by `(hash(Key), Key, Val, Time)`.
///
/// Specifically, this means that we attempt to place any `Key` at `alloc_len * (hash(Key) / 2^64)`,
/// and spill onward if the slot is occupied. The cleverness of RHH is that you may instead evict
/// someone else, in order to maintain the ordering up above. In fact, that is basically the rule:
/// when there is a conflict, evict the greater of the two and attempt to place it in the next slot.
///
/// This RHH implementation uses a repeated `keys_offs` offset to indicate an absent element, as all
/// keys for valid updates must have some associated values with updates. This is the same type of
/// optimization made for repeated updates, and it rules out (here) using that trick for repeated values.
///
/// We will use the `Hashable` trait here, but any consistent hash function should work out ok.
/// We specifically want to use the highest bits of the result (we will) because the low bits have
/// likely been spent shuffling the data between workers (by key), and are likely low entropy.
#[derive(Debug, Serialize, Deserialize)]
pub struct RhhValStorage<L: Layout>
where
<L::Target as Update>::Key: Default + HashOrdered,
{
/// The requested capacity for `keys`. We use this when determining where a key with a certain hash
/// would most like to end up. The `BatchContainer` trait does not provide a `capacity()` method,
/// otherwise we would just use that.
pub key_capacity: usize,
/// A number large enough that when it divides any `u64` the result is at most `self.key_capacity`.
/// When that capacity is zero or one, this is set to zero instead.
pub divisor: u64,
/// The number of present keys, distinct from `keys.len()` which contains
pub key_count: usize,
/// An ordered list of keys, corresponding to entries in `keys_offs`.
pub keys: L::KeyContainer,
/// Offsets used to provide indexes from keys to values.
///
/// The length of this list is one longer than `keys`, so that we can avoid bounds logic.
pub keys_offs: L::OffsetContainer,
/// Concatenated ordered lists of values, bracketed by offsets in `keys_offs`.
pub vals: L::ValContainer,
/// Offsets used to provide indexes from values to updates.
///
/// This list has a special representation that any empty range indicates the singleton
/// element just before the range, as if the start were decremented by one. The empty
/// range is otherwise an invalid representation, and we borrow it to compactly encode
/// single common update values (e.g. in a snapshot, the minimal time and a diff of one).
///
/// The length of this list is one longer than `vals`, so that we can avoid bounds logic.
pub vals_offs: L::OffsetContainer,
/// Concatenated ordered lists of update times, bracketed by offsets in `vals_offs`.
pub times: L::TimeContainer,
/// Concatenated ordered lists of update diffs, bracketed by offsets in `vals_offs`.
pub diffs: L::DiffContainer,
}
impl<L: Layout> RhhValStorage<L>
where
<L::Target as Update>::Key: Default + HashOrdered,
for<'a> <L::KeyContainer as BatchContainer>::ReadItem<'a>: HashOrdered,
{
/// Lower and upper bounds in `self.vals` corresponding to the key at `index`.
fn values_for_key(&self, index: usize) -> (usize, usize) {
let lower = self.keys_offs.index(index);
let upper = self.keys_offs.index(index+1);
// Looking up values for an invalid key indicates something is wrong.
assert!(lower < upper, "{:?} v {:?} at {:?}", lower, upper, index);
(lower, upper)
}
/// Lower and upper bounds in `self.updates` corresponding to the value at `index`.
fn updates_for_value(&self, index: usize) -> (usize, usize) {
let mut lower = self.vals_offs.index(index);
let upper = self.vals_offs.index(index+1);
// We use equal lower and upper to encode "singleton update; just before here".
// It should only apply when there is a prior element, so `lower` should be greater than zero.
if lower == upper {
assert!(lower > 0);
lower -= 1;
}
(lower, upper)
}
/// Inserts the key at its desired location, or nearby.
///
/// Because there may be collisions, they key may be placed just after its desired location.
/// If necessary, this method will introduce default keys and copy the offsets to create space
/// after which to insert the key. These will be indicated by `None` entries in the `hash` vector.
///
/// If `offset` is specified, we will insert it at the appropriate location. If it is not specified,
/// we leave `keys_offs` ready to receive it as the next `push`. This is so that builders that may
/// not know the final offset at the moment of key insertion can prepare for receiving the offset.
fn insert_key(&mut self, key: <L::KeyContainer as BatchContainer>::ReadItem<'_>, offset: Option<usize>) {
let desired = self.desired_location(&key);
// Were we to push the key now, it would be at `self.keys.len()`, so while that is wrong,
// push additional blank entries in.
while self.keys.len() < desired {
// We insert a default (dummy) key and repeat the offset to indicate this.
let current_offset = self.keys_offs.index(self.keys.len());
self.keys.push(<<L::Target as Update>::Key as Default>::default());
self.keys_offs.push(current_offset);
}
// Now we insert the key. Even if it is no longer the desired location because of contention.
// If an offset has been supplied we insert it, and otherwise leave it for future determination.
self.keys.push(key);
if let Some(offset) = offset {
self.keys_offs.push(offset);
}
self.key_count += 1;
}
/// Indicates both the desired location and the hash signature of the key.
fn desired_location<K: Hashable>(&self, key: &K) -> usize {
if self.divisor == 0 { 0 }
else {
(key.hashed().into() / self.divisor).try_into().expect("divisor not large enough to force u64 into uisze")
}
}
/// Returns true if one should advance one's index in the search for `key`.
fn advance_key(&self, index: usize, key: <L::KeyContainer as BatchContainer>::ReadItem<'_>) -> bool {
// Ideally this short-circuits, as `self.keys[index]` is bogus data.
!self.live_key(index) || self.keys.index(index).lt(&<L::KeyContainer as BatchContainer>::reborrow(key))
}
/// Indicates that a key is valid, rather than dead space, by looking for a valid offset range.
fn live_key(&self, index: usize) -> bool {
self.keys_offs.index(index) != self.keys_offs.index(index+1)
}
/// Advances `index` until it references a live key, or is `keys.len()`.
fn advance_to_live_key(&self, index: &mut usize) {
while *index < self.keys.len() && !self.live_key(*index) {
*index += 1;
}
}
/// A value large enough that any `u64` divided by it is less than `capacity`.
///
/// This is `2^64 / capacity`, except in the cases where `capacity` is zero or one.
/// In those cases, we'll return `0` to communicate the exception, for which we should
/// just return `0` when announcing a target location (and a zero capacity that we insert
/// into becomes a bug).
fn divisor_for_capacity(capacity: usize) -> u64 {
let capacity: u64 = capacity.try_into().expect("usize exceeds u64");
if capacity == 0 || capacity == 1 { 0 }
else {
((1 << 63) / capacity) << 1
}
}
}
/// An immutable collection of update tuples, from a contiguous interval of logical times.
///
/// The `L` parameter captures how the updates should be laid out, and `C` determines which
/// merge batcher to select.
#[derive(Serialize, Deserialize)]
#[serde(bound = "
L::KeyContainer: Serialize + for<'a> Deserialize<'a>,
L::ValContainer: Serialize + for<'a> Deserialize<'a>,
L::OffsetContainer: Serialize + for<'a> Deserialize<'a>,
L::TimeContainer: Serialize + for<'a> Deserialize<'a>,
L::DiffContainer: Serialize + for<'a> Deserialize<'a>,
")]
pub struct RhhValBatch<L: Layout>
where
<L::Target as Update>::Key: Default + HashOrdered,
{
/// The updates themselves.
pub storage: RhhValStorage<L>,
/// Description of the update times this layer represents.
pub description: Description<<L::Target as Update>::Time>,
/// The number of updates reflected in the batch.
///
/// We track this separately from `storage` because due to the singleton optimization,
/// we may have many more updates than `storage.updates.len()`. It should equal that
/// length, plus the number of singleton optimizations employed.
pub updates: usize,
}
impl<L: Layout> BatchReader for RhhValBatch<L>
where
<L::Target as Update>::Key: Default + HashOrdered,
for<'a> <L::KeyContainer as BatchContainer>::ReadItem<'a>: HashOrdered,
{
type Key<'a> = <L::KeyContainer as BatchContainer>::ReadItem<'a>;
type Val<'a> = <L::ValContainer as BatchContainer>::ReadItem<'a>;
type Time = <L::Target as Update>::Time;
type TimeGat<'a> = <L::TimeContainer as BatchContainer>::ReadItem<'a>;
type Diff = <L::Target as Update>::Diff;
type DiffGat<'a> = <L::DiffContainer as BatchContainer>::ReadItem<'a>;
type Cursor = RhhValCursor<L>;
fn cursor(&self) -> Self::Cursor {
let mut cursor = RhhValCursor {
key_cursor: 0,
val_cursor: 0,
phantom: std::marker::PhantomData,
};
cursor.step_key(self);
cursor
}
fn len(&self) -> usize {
// Normally this would be `self.updates.len()`, but we have a clever compact encoding.
// Perhaps we should count such exceptions to the side, to provide a correct accounting.
self.updates
}
fn description(&self) -> &Description<<L::Target as Update>::Time> { &self.description }
}
impl<L: Layout> Batch for RhhValBatch<L>
where
<L::Target as Update>::Key: Default + HashOrdered,
for<'a> <L::KeyContainer as BatchContainer>::ReadItem<'a>: HashOrdered,
{
type Merger = RhhValMerger<L>;
fn begin_merge(&self, other: &Self, compaction_frontier: AntichainRef<<L::Target as Update>::Time>) -> Self::Merger {
RhhValMerger::new(self, other, compaction_frontier)
}
}
/// State for an in-progress merge.
pub struct RhhValMerger<L: Layout>
where
<L::Target as Update>::Key: Default + HashOrdered,
{
/// Key position to merge next in the first batch.
key_cursor1: usize,
/// Key position to merge next in the second batch.
key_cursor2: usize,
/// result that we are currently assembling.
result: RhhValStorage<L>,
/// description
description: Description<<L::Target as Update>::Time>,
/// Local stash of updates, to use for consolidation.
///
/// We could emulate a `ChangeBatch` here, with related compaction smarts.
/// A `ChangeBatch` itself needs an `i64` diff type, which we have not.
update_stash: Vec<(<L::Target as Update>::Time, <L::Target as Update>::Diff)>,
/// Counts the number of singleton-optimized entries, that we may correctly count the updates.
singletons: usize,
}
impl<L: Layout> Merger<RhhValBatch<L>> for RhhValMerger<L>
where
<L::Target as Update>::Key: Default + HashOrdered,
RhhValBatch<L>: Batch<Time=<L::Target as Update>::Time>,
for<'a> <L::KeyContainer as BatchContainer>::ReadItem<'a>: HashOrdered,
{
fn new(batch1: &RhhValBatch<L>, batch2: &RhhValBatch<L>, compaction_frontier: AntichainRef<<L::Target as Update>::Time>) -> Self {
assert!(batch1.upper() == batch2.lower());
use crate::lattice::Lattice;
let mut since = batch1.description().since().join(batch2.description().since());
since = since.join(&compaction_frontier.to_owned());
let description = Description::new(batch1.lower().clone(), batch2.upper().clone(), since);
// This is a massive overestimate on the number of keys, but we don't have better information.
// An over-estimate can be a massive problem as well, with sparse regions being hard to cross.
let max_cap = batch1.len() + batch2.len();
let rhh_cap = 2 * max_cap;
let batch1 = &batch1.storage;
let batch2 = &batch2.storage;
let mut storage = RhhValStorage {
keys: L::KeyContainer::merge_capacity(&batch1.keys, &batch2.keys),
keys_offs: L::OffsetContainer::with_capacity(batch1.keys_offs.len() + batch2.keys_offs.len()),
vals: L::ValContainer::merge_capacity(&batch1.vals, &batch2.vals),
vals_offs: L::OffsetContainer::with_capacity(batch1.vals_offs.len() + batch2.vals_offs.len()),
times: L::TimeContainer::merge_capacity(&batch1.times, &batch2.times),
diffs: L::DiffContainer::merge_capacity(&batch1.diffs, &batch2.diffs),
key_count: 0,
key_capacity: rhh_cap,
divisor: RhhValStorage::<L>::divisor_for_capacity(rhh_cap),
};
// Mark explicit types because type inference fails to resolve it.
let keys_offs: &mut L::OffsetContainer = &mut storage.keys_offs;
keys_offs.push(0);
let vals_offs: &mut L::OffsetContainer = &mut storage.vals_offs;
vals_offs.push(0);
RhhValMerger {
key_cursor1: 0,
key_cursor2: 0,
result: storage,
description,
update_stash: Vec::new(),
singletons: 0,
}
}
fn done(self) -> RhhValBatch<L> {
RhhValBatch {
updates: self.result.times.len() + self.singletons,
storage: self.result,
description: self.description,
}
}
fn work(&mut self, source1: &RhhValBatch<L>, source2: &RhhValBatch<L>, fuel: &mut isize) {
// An (incomplete) indication of the amount of work we've done so far.
let starting_updates = self.result.times.len();
let mut effort = 0isize;
source1.storage.advance_to_live_key(&mut self.key_cursor1);
source2.storage.advance_to_live_key(&mut self.key_cursor2);
// While both mergees are still active, perform single-key merges.
while self.key_cursor1 < source1.storage.keys.len() && self.key_cursor2 < source2.storage.keys.len() && effort < *fuel {
self.merge_key(&source1.storage, &source2.storage);
source1.storage.advance_to_live_key(&mut self.key_cursor1);
source2.storage.advance_to_live_key(&mut self.key_cursor2);
// An (incomplete) accounting of the work we've done.
effort = (self.result.times.len() - starting_updates) as isize;
}
// Merging is complete, and only copying remains.
// Key-by-key copying allows effort interruption, and compaction.
while self.key_cursor1 < source1.storage.keys.len() && effort < *fuel {
self.copy_key(&source1.storage, self.key_cursor1);
self.key_cursor1 += 1;
source1.storage.advance_to_live_key(&mut self.key_cursor1);
effort = (self.result.times.len() - starting_updates) as isize;
}
while self.key_cursor2 < source2.storage.keys.len() && effort < *fuel {
self.copy_key(&source2.storage, self.key_cursor2);
self.key_cursor2 += 1;
source2.storage.advance_to_live_key(&mut self.key_cursor2);
effort = (self.result.times.len() - starting_updates) as isize;
}
*fuel -= effort;
}
}
// Helper methods in support of merging batches.
impl<L: Layout> RhhValMerger<L>
where
<L::Target as Update>::Key: Default + HashOrdered,
for<'a> <L::KeyContainer as BatchContainer>::ReadItem<'a>: HashOrdered,
{
/// Copy the next key in `source`.
///
/// The method extracts the key in `source` at `cursor`, and merges it in to `self`.
/// If the result does not wholly cancel, they key will be present in `self` with the
/// compacted values and updates.
///
/// The caller should be certain to update the cursor, as this method does not do this.
fn copy_key(&mut self, source: &RhhValStorage<L>, cursor: usize) {
// Capture the initial number of values to determine if the merge was ultimately non-empty.
let init_vals = self.result.vals.len();
let (mut lower, upper) = source.values_for_key(cursor);
while lower < upper {
self.stash_updates_for_val(source, lower);
if let Some(off) = self.consolidate_updates() {
self.result.vals_offs.push(off);
self.result.vals.push(source.vals.index(lower));
}
lower += 1;
}
// If we have pushed any values, copy the key as well.
if self.result.vals.len() > init_vals {
self.result.insert_key(source.keys.index(cursor), Some(self.result.vals.len()));
}
}
/// Merge the next key in each of `source1` and `source2` into `self`, updating the appropriate cursors.
///
/// This method only merges a single key. It applies all compaction necessary, and may result in no output
/// if the updates cancel either directly or after compaction.
fn merge_key(&mut self, source1: &RhhValStorage<L>, source2: &RhhValStorage<L>) {
use ::std::cmp::Ordering;
match source1.keys.index(self.key_cursor1).cmp(&source2.keys.index(self.key_cursor2)) {
Ordering::Less => {
self.copy_key(source1, self.key_cursor1);
self.key_cursor1 += 1;
},
Ordering::Equal => {
// Keys are equal; must merge all values from both sources for this one key.
let (lower1, upper1) = source1.values_for_key(self.key_cursor1);
let (lower2, upper2) = source2.values_for_key(self.key_cursor2);
if let Some(off) = self.merge_vals((source1, lower1, upper1), (source2, lower2, upper2)) {
self.result.insert_key(source1.keys.index(self.key_cursor1), Some(off));
}
// Increment cursors in either case; the keys are merged.
self.key_cursor1 += 1;
self.key_cursor2 += 1;
},
Ordering::Greater => {
self.copy_key(source2, self.key_cursor2);
self.key_cursor2 += 1;
},
}
}
/// Merge two ranges of values into `self`.
///
/// If the compacted result contains values with non-empty updates, the function returns
/// an offset that should be recorded to indicate the upper extent of the result values.
fn merge_vals(
&mut self,
(source1, mut lower1, upper1): (&RhhValStorage<L>, usize, usize),
(source2, mut lower2, upper2): (&RhhValStorage<L>, usize, usize),
) -> Option<usize> {
// Capture the initial number of values to determine if the merge was ultimately non-empty.
let init_vals = self.result.vals.len();
while lower1 < upper1 && lower2 < upper2 {
// We compare values, and fold in updates for the lowest values;
// if they are non-empty post-consolidation, we write the value.
// We could multi-way merge and it wouldn't be very complicated.
use ::std::cmp::Ordering;
match source1.vals.index(lower1).cmp(&source2.vals.index(lower2)) {
Ordering::Less => {
// Extend stash by updates, with logical compaction applied.
self.stash_updates_for_val(source1, lower1);
if let Some(off) = self.consolidate_updates() {
self.result.vals_offs.push(off);
self.result.vals.push(source1.vals.index(lower1));
}
lower1 += 1;
},
Ordering::Equal => {
self.stash_updates_for_val(source1, lower1);
self.stash_updates_for_val(source2, lower2);
if let Some(off) = self.consolidate_updates() {
self.result.vals_offs.push(off);
self.result.vals.push(source1.vals.index(lower1));
}
lower1 += 1;
lower2 += 1;
},
Ordering::Greater => {
// Extend stash by updates, with logical compaction applied.
self.stash_updates_for_val(source2, lower2);
if let Some(off) = self.consolidate_updates() {
self.result.vals_offs.push(off);
self.result.vals.push(source2.vals.index(lower2));
}
lower2 += 1;
},
}
}
// Merging is complete, but we may have remaining elements to push.
while lower1 < upper1 {
self.stash_updates_for_val(source1, lower1);
if let Some(off) = self.consolidate_updates() {
self.result.vals_offs.push(off);
self.result.vals.push(source1.vals.index(lower1));
}
lower1 += 1;
}
while lower2 < upper2 {
self.stash_updates_for_val(source2, lower2);
if let Some(off) = self.consolidate_updates() {
self.result.vals_offs.push(off);
self.result.vals.push(source2.vals.index(lower2));
}
lower2 += 1;
}
// Values being pushed indicate non-emptiness.
if self.result.vals.len() > init_vals {
Some(self.result.vals.len())
} else {
None
}
}
/// Transfer updates for an indexed value in `source` into `self`, with compaction applied.
fn stash_updates_for_val(&mut self, source: &RhhValStorage<L>, index: usize) {
let (lower, upper) = source.updates_for_value(index);
for i in lower .. upper {
// NB: Here is where we would need to look back if `lower == upper`.
let time = source.times.index(i);
let diff = source.diffs.index(i);
let mut new_time = time.into_owned();
use crate::lattice::Lattice;
new_time.advance_by(self.description.since().borrow());
self.update_stash.push((new_time, diff.into_owned()));
}
}
/// Consolidates `self.updates_stash` and produces the offset to record, if any.
fn consolidate_updates(&mut self) -> Option<usize> {
use crate::consolidation;
consolidation::consolidate(&mut self.update_stash);
if !self.update_stash.is_empty() {
// If there is a single element, equal to a just-prior recorded update,
// we push nothing and report an unincremented offset to encode this case.
let time_diff = self.result.times.last().zip(self.result.diffs.last());
let last_eq = self.update_stash.last().zip(time_diff).map(|((t1, d1), (t2, d2))| {
let t1 = <<L::TimeContainer as BatchContainer>::ReadItem<'_> as IntoOwned>::borrow_as(t1);
let d1 = <<L::DiffContainer as BatchContainer>::ReadItem<'_> as IntoOwned>::borrow_as(d1);
t1.eq(&t2) && d1.eq(&d2)
});
if self.update_stash.len() == 1 && last_eq.unwrap_or(false) {
// Just clear out update_stash, as we won't drain it here.
self.update_stash.clear();
self.singletons += 1;
}
else {
// Conventional; move `update_stash` into `updates`.
for (time, diff) in self.update_stash.drain(..) {
self.result.times.push(time);
self.result.diffs.push(diff);
}
}
Some(self.result.times.len())
} else {
None
}
}
}
/// A cursor through a Robin Hood Hashed list of keys, vals, and such.
///
/// The important detail is that not all of `keys` represent valid keys.
/// We must consult `storage.hashed` to see if the associated data is valid.
/// Importantly, we should skip over invalid keys, rather than report them as
/// invalid through `key_valid`: that method is meant to indicate the end of
/// the cursor, rather than internal state.
pub struct RhhValCursor<L: Layout>
where
<L::Target as Update>::Key: Default + HashOrdered,
{
/// Absolute position of the current key.
key_cursor: usize,
/// Absolute position of the current value.
val_cursor: usize,
/// Phantom marker for Rust happiness.
phantom: PhantomData<L>,
}
impl<L: Layout> Cursor for RhhValCursor<L>
where
<L::Target as Update>::Key: Default + HashOrdered,
for<'a> <L::KeyContainer as BatchContainer>::ReadItem<'a>: HashOrdered,
{
type Key<'a> = <L::KeyContainer as BatchContainer>::ReadItem<'a>;
type Val<'a> = <L::ValContainer as BatchContainer>::ReadItem<'a>;
type Time = <L::Target as Update>::Time;
type TimeGat<'a> = <L::TimeContainer as BatchContainer>::ReadItem<'a>;
type Diff = <L::Target as Update>::Diff;
type DiffGat<'a> = <L::DiffContainer as BatchContainer>::ReadItem<'a>;
type Storage = RhhValBatch<L>;
fn key<'a>(&self, storage: &'a RhhValBatch<L>) -> Self::Key<'a> {
storage.storage.keys.index(self.key_cursor)
}
fn val<'a>(&self, storage: &'a RhhValBatch<L>) -> Self::Val<'a> { storage.storage.vals.index(self.val_cursor) }
fn map_times<L2: FnMut(Self::TimeGat<'_>, Self::DiffGat<'_>)>(&mut self, storage: &RhhValBatch<L>, mut logic: L2) {
let (lower, upper) = storage.storage.updates_for_value(self.val_cursor);
for index in lower .. upper {
let time = storage.storage.times.index(index);
let diff = storage.storage.diffs.index(index);
logic(time, diff);
}
}
fn key_valid(&self, storage: &RhhValBatch<L>) -> bool { self.key_cursor < storage.storage.keys.len() }
fn val_valid(&self, storage: &RhhValBatch<L>) -> bool { self.val_cursor < storage.storage.values_for_key(self.key_cursor).1 }
fn step_key(&mut self, storage: &RhhValBatch<L>){
// We advance the cursor by one for certain, and then as long as we need to find a valid key.
self.key_cursor += 1;
storage.storage.advance_to_live_key(&mut self.key_cursor);
if self.key_valid(storage) {
self.rewind_vals(storage);
}
else {
self.key_cursor = storage.storage.keys.len();
}
}
fn seek_key(&mut self, storage: &RhhValBatch<L>, key: Self::Key<'_>) {
// self.key_cursor += storage.storage.keys.advance(self.key_cursor, storage.storage.keys.len(), |x| x.lt(key));
let desired = storage.storage.desired_location(&key);
// Advance the cursor, if `desired` is ahead of it.
if self.key_cursor < desired {
self.key_cursor = desired;
}
// Advance the cursor as long as we have not found a value greater or equal to `key`.
// We may have already passed `key`, and confirmed its absence, but our goal is to
// find the next key afterwards so that users can, for example, alternately iterate.
while self.key_valid(storage) && storage.storage.advance_key(self.key_cursor, key) {
// TODO: Based on our encoding, we could skip logarithmically over empty regions by galloping
// through `storage.keys_offs`, which stays put for dead space.
self.key_cursor += 1;
}
if self.key_valid(storage) {
self.rewind_vals(storage);
}
}
fn step_val(&mut self, storage: &RhhValBatch<L>) {
self.val_cursor += 1;
if !self.val_valid(storage) {
self.val_cursor = storage.storage.values_for_key(self.key_cursor).1;
}
}
fn seek_val(&mut self, storage: &RhhValBatch<L>, val: Self::Val<'_>) {
self.val_cursor += storage.storage.vals.advance(self.val_cursor, storage.storage.values_for_key(self.key_cursor).1, |x| <L::ValContainer as BatchContainer>::reborrow(x).lt(&<L::ValContainer as BatchContainer>::reborrow(val)));
}
fn rewind_keys(&mut self, storage: &RhhValBatch<L>) {
self.key_cursor = 0;
storage.storage.advance_to_live_key(&mut self.key_cursor);
if self.key_valid(storage) {
self.rewind_vals(storage)
}
}
fn rewind_vals(&mut self, storage: &RhhValBatch<L>) {
self.val_cursor = storage.storage.values_for_key(self.key_cursor).0;
}
}
/// A builder for creating layers from unsorted update tuples.
pub struct RhhValBuilder<L: Layout, CI>
where
<L::Target as Update>::Key: Default + HashOrdered,
{
result: RhhValStorage<L>,
singleton: Option<(<L::Target as Update>::Time, <L::Target as Update>::Diff)>,
/// Counts the number of singleton optimizations we performed.
///
/// This number allows us to correctly gauge the total number of updates reflected in a batch,
/// even though `updates.len()` may be much shorter than this amount.
singletons: usize,
_marker: PhantomData<CI>,
}
impl<L: Layout, CI> RhhValBuilder<L, CI>
where
<L::Target as Update>::Key: Default + HashOrdered,
{
/// Pushes a single update, which may set `self.singleton` rather than push.
///
/// This operation is meant to be equivalent to `self.results.updates.push((time, diff))`.
/// However, for "clever" reasons it does not do this. Instead, it looks for opportunities
/// to encode a singleton update with an "absert" update: repeating the most recent offset.
/// This otherwise invalid state encodes "look back one element".
///
/// When `self.singleton` is `Some`, it means that we have seen one update and it matched the
/// previously pushed update exactly. In that case, we do not push the update into `updates`.
/// The update tuple is retained in `self.singleton` in case we see another update and need
/// to recover the singleton to push it into `updates` to join the second update.
fn push_update(&mut self, time: <L::Target as Update>::Time, diff: <L::Target as Update>::Diff) {
// If a just-pushed update exactly equals `(time, diff)` we can avoid pushing it.
let t1 = <<L::TimeContainer as BatchContainer>::ReadItem<'_> as IntoOwned>::borrow_as(&time);
let d1 = <<L::DiffContainer as BatchContainer>::ReadItem<'_> as IntoOwned>::borrow_as(&diff);
if self.result.times.last().map(|t| t == t1).unwrap_or(false) && self.result.diffs.last().map(|d| d == d1).unwrap_or(false) {
assert!(self.singleton.is_none());
self.singleton = Some((time, diff));
}
else {
// If we have pushed a single element, we need to copy it out to meet this one.
if let Some((time, diff)) = self.singleton.take() {
self.result.times.push(time);
self.result.diffs.push(diff);
}
self.result.times.push(time);
self.result.diffs.push(diff);
}
}
}
impl<L: Layout, CI> Builder for RhhValBuilder<L, CI>
where
<L::Target as Update>::Key: Default + HashOrdered,
CI: for<'a> BuilderInput<L::KeyContainer, L::ValContainer, Key<'a> = <L::Target as Update>::Key, Time=<L::Target as Update>::Time, Diff=<L::Target as Update>::Diff>,
for<'a> L::ValContainer: PushInto<CI::Val<'a>>,
for<'a> <L::KeyContainer as BatchContainer>::ReadItem<'a>: HashOrdered + IntoOwned<'a, Owned = <L::Target as Update>::Key>,
{
type Input = CI;
type Time = <L::Target as Update>::Time;
type Output = RhhValBatch<L>;
fn with_capacity(keys: usize, vals: usize, upds: usize) -> Self {
// Double the capacity for RHH; probably excessive.
let rhh_capacity = 2 * keys;
let divisor = RhhValStorage::<L>::divisor_for_capacity(rhh_capacity);
// We want some additive slop, in case we spill over.
// This number magically chosen based on nothing in particular.
// Worst case, we will re-alloc and copy if we spill beyond this.
let keys = rhh_capacity + 10;
// We don't introduce zero offsets as they will be introduced by the first `push` call.
Self {
result: RhhValStorage {
keys: L::KeyContainer::with_capacity(keys),
keys_offs: L::OffsetContainer::with_capacity(keys + 1),
vals: L::ValContainer::with_capacity(vals),
vals_offs: L::OffsetContainer::with_capacity(vals + 1),
times: L::TimeContainer::with_capacity(upds),
diffs: L::DiffContainer::with_capacity(upds),
key_count: 0,
key_capacity: rhh_capacity,
divisor,
},
singleton: None,
singletons: 0,
_marker: PhantomData,
}
}
#[inline]
fn push(&mut self, chunk: &mut Self::Input) {
for item in chunk.drain() {
let (key, val, time, diff) = CI::into_parts(item);
// Perhaps this is a continuation of an already received key.
if self.result.keys.last().map(|k| CI::key_eq(&key, k)).unwrap_or(false) {
// Perhaps this is a continuation of an already received value.
if self.result.vals.last().map(|v| CI::val_eq(&val, v)).unwrap_or(false) {
self.push_update(time, diff);
} else {
// New value; complete representation of prior value.
self.result.vals_offs.push(self.result.times.len());
if self.singleton.take().is_some() { self.singletons += 1; }
self.push_update(time, diff);
self.result.vals.push(val);
}
} else {
// New key; complete representation of prior key.
self.result.vals_offs.push(self.result.times.len());
if self.singleton.take().is_some() { self.singletons += 1; }
self.result.keys_offs.push(self.result.vals.len());
self.push_update(time, diff);
self.result.vals.push(val);
// Insert the key, but with no specified offset.
self.result.insert_key(IntoOwned::borrow_as(&key), None);
}
}
}
#[inline(never)]
fn done(mut self, lower: Antichain<Self::Time>, upper: Antichain<Self::Time>, since: Antichain<Self::Time>) -> RhhValBatch<L> {
// Record the final offsets
self.result.vals_offs.push(self.result.times.len());
// Remove any pending singleton, and if it was set increment our count.
if self.singleton.take().is_some() { self.singletons += 1; }
self.result.keys_offs.push(self.result.vals.len());
RhhValBatch {
updates: self.result.times.len() + self.singletons,
storage: self.result,
description: Description::new(lower, upper, since),
}
}
}
}
mod key_batch {
// Copy the above, once it works!
}