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Differential D6428

rust-discovery: using the children cache in add_missing
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Authored by gracinet on May 22 2019, 1:00 PM.

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Reviewers
kevincox
Group Reviewers
hg-reviewers
Commits
rHG8c9a6adec67a: rust-discovery: using the children cache in add_missing
Summary

The DAG range computation often needs to get back to very old
revisions, and turns out to be disproportionately long, given
that the end goal is to remove the descendents of the given
missing revisons from the undecided set.

The fast iteration capabilities available in the Rust case make
it possible to avoid the DAG range entirely, at the cost of
precomputing the children cache, and to simply iterate on
children of the given missing revisions.

This is a case where staying on the same side of the interface
between the two languages has clear benefits.

On discoveries with initial undecided sets
small enough to bypass sampling entirely, the total cost of
computing the children cache and the subsequent iteration
becomes better than the Python + C counterpart, which relies on
reachableroots2.

For example, on a repo with more than one million revisions with
an initial undecided set of 11 elements, we get these figures:

Rust version with simple iteration

addcommons: 57.287us
first undecided computation: 184.278334ms
first children cache computation: 131.056us
addmissings iteration: 42.766us
first addinfo total: 185.24 ms

Python + C version

first addcommons: 0.29 ms
addcommons 0.21 ms
first undecided computation 191.35 ms
addmissings 45.75 ms
first addinfo total: 237.77 ms

On discoveries with large undecided sets, the initial price paid
makes the first addinfo slower than the Python + C version,
but that's more than compensated by the gain in sampling and
subsequent iterations.
Here's an extreme example with an undecided set of a million revisions:

Rust version:

first undecided computation: 293.842629ms
first children cache computation: 407.911297ms
addmissings iteration: 34.312869ms
first addinfo total: 776.02 ms
taking initial sample
query 2: sampling time: 1318.38 ms
query 2; still undecided: 1005013, sample size is: 200
addmissings: 143.062us

Python + C version:

first undecided computation 298.13 ms
addmissings 80.13 ms
first addinfo total: 399.62 ms
taking initial sample
query 2: sampling time: 3957.23 ms
query 2; still undecided: 1005013, sample size is: 200
addmissings 52.88 ms

Diff Detail

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Event Timeline

gracinet created this revision.May 22 2019, 1:00 PM
gracinet added a comment.May 22 2019, 1:17 PM

This revision is new. At the time I submitted the previous series, it was almost always the case that the advantage of the C reachableroots2() over the Rust `dagop::range() was more than compensated by sampling been done in Rust instead of Python.
I originally planned to finish that one and submit it as a follow-up optimization, but now it's necessary to prevent being slower in the fastest cases where there's no sampling.

kevincox accepted this revision.Jun 10 2019, 8:59 AM
kevincox added inline comments.
rust/hg-core/src/discovery.rs
243

These added comments seem more relevant to the implementation of the method than they are to the caller. Would it make sense to move them inside of the function body so that they don't busy the doc-comment?

gracinet updated this revision to Diff 15471.Jun 12 2019, 2:17 PM
gracinet updated this revision to Diff 15485.Jun 13 2019, 9:33 AM
gracinet added inline comments.Jun 13 2019, 9:38 AM
rust/hg-core/src/discovery.rs
243

Yes, you're right, I replaced it with a "Performance note" section for the callers.
As for the rationale for the change, I think that the commit message is more than enough.

gracinet added a commit: rHG8c9a6adec67a: rust-discovery: using the children cache in add_missing.Aug 14 2019, 4:16 PM
This revision was not accepted when it landed; it landed in state Needs Review.
Closed by commit rHG8c9a6adec67a: rust-discovery: using the children cache in add_missing (authored by gracinet). · Explain Why
This revision was automatically updated to reflect the committed changes.

Revision Contents
Changeset List

PathPackages
Mrust/hg-core/src/discovery.rs (61 lines)

Diff 15485

rust/hg-core/src/discovery.rs

self.common.add_bases(common); self.common.add_bases(common);
if let Some(ref mut undecided) = self.undecided { if let Some(ref mut undecided) = self.undecided {
self.common.remove_ancestors_from(undecided)?; self.common.remove_ancestors_from(undecided)?;
} }
Ok(()) Ok(())
} }
/// Register revisions known as being missing /// Register revisions known as being missing
///
/// # Performance note
///
/// Except in the most trivial case, the first call of this method has
/// the side effect of computing `self.undecided` set for the first time,
/// and the related caches it might need for efficiency of its internal
/// computation. This is typically faster if more information is
/// available in `self.common`. Therefore, for good performance, the
kevincoxUnsubmitted
Not Done

These added comments seem more relevant to the implementation of the method than they are to the caller. Would it make sense to move them inside of the function body so that they don't busy the doc-comment?

kevincox: These added comments seem more relevant to the implementation of the method than they are to…
gracinetAuthorUnsubmitted
Done

Yes, you're right, I replaced it with a "Performance note" section for the callers.
As for the rationale for the change, I think that the commit message is more than enough.

gracinet: Yes, you're right, I replaced it with a "Performance note" section for the callers. As for the…
/// caller should avoid calling this too early.
pub fn add_missing_revisions( pub fn add_missing_revisions(
&mut self, &mut self,
missing: impl IntoIterator<Item = Revision>, missing: impl IntoIterator<Item = Revision>,
) -> Result<(), GraphError> { ) -> Result<(), GraphError> {
self.ensure_undecided()?; self.ensure_children_cache()?;
let range = dagops::range( self.ensure_undecided()?; // for safety of possible future refactors
&self.graph, let children = self.children_cache.as_ref().unwrap();
missing, let mut seen: HashSet<Revision> = HashSet::new();
self.undecided.as_ref().unwrap().iter().cloned(), let mut tovisit: VecDeque<Revision> = missing.into_iter().collect();
)?;
let undecided_mut = self.undecided.as_mut().unwrap(); let undecided_mut = self.undecided.as_mut().unwrap();
for missrev in range { while let Some(rev) = tovisit.pop_front() {
self.missing.insert(missrev); if !self.missing.insert(rev) {
undecided_mut.remove(&missrev); // either it's known to be missing from a previous
// invocation, and there's no need to iterate on its
// children (we now they are all missing)
// or it's from a previous iteration of this loop
// and its children have already been queued
continue;
}
undecided_mut.remove(&rev);
match children.get(&rev) {
None => {
continue;
}
Some(this_children) => {
for child in this_children.iter().cloned() {
if seen.insert(child) {
tovisit.push_back(child);
}
}
}
}
} }
Ok(()) Ok(())
} }
/// Do we have any information about the peer? /// Do we have any information about the peer?
pub fn has_info(&self) -> bool { pub fn has_info(&self) -> bool {
self.common.has_bases() self.common.has_bases()
} }
assert_eq!(sorted_undecided(&disco), vec![]); assert_eq!(sorted_undecided(&disco), vec![]);
assert_eq!(sorted_missing(&disco), vec![8, 10, 13]); assert_eq!(sorted_missing(&disco), vec![8, 10, 13]);
assert!(disco.is_complete()); assert!(disco.is_complete());
assert_eq!(sorted_common_heads(&disco)?, vec![5, 11, 12]); assert_eq!(sorted_common_heads(&disco)?, vec![5, 11, 12]);
Ok(()) Ok(())
} }
#[test] #[test]
fn test_add_missing_early_continue() -> Result<(), GraphError> {
eprintln!("test_add_missing_early_stop");
let mut disco = full_disco();
disco.add_common_revisions(vec![13, 3, 4])?;
disco.ensure_children_cache()?;
// 12 is grand-child of 6 through 9
// passing them in this order maximizes the chances of the
// early continue to do the wrong thing
disco.add_missing_revisions(vec![6, 9, 12])?;
assert_eq!(sorted_undecided(&disco), vec![5, 7, 10, 11]);
assert_eq!(sorted_missing(&disco), vec![6, 9, 12]);
assert!(!disco.is_complete());
Ok(())
}
#[test]
fn test_limit_sample_no_need_to() { fn test_limit_sample_no_need_to() {
let sample = vec![1, 2, 3, 4]; let sample = vec![1, 2, 3, 4];
assert_eq!(full_disco().limit_sample(sample, 10), vec![1, 2, 3, 4]); assert_eq!(full_disco().limit_sample(sample, 10), vec![1, 2, 3, 4]);
} }
#[test] #[test]
fn test_limit_sample_less_than_half() { fn test_limit_sample_less_than_half() {
assert_eq!(full_disco().limit_sample((1..6).collect(), 2), vec![4, 2]); assert_eq!(full_disco().limit_sample((1..6).collect(), 2), vec![4, 2]);