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feat: Implement TryInto to convert Signature and SigStore into KmerMinHash #3348

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merged 2 commits into from
Oct 13, 2024

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@luizirber luizirber commented Oct 12, 2024

Ref: https://github.com/sourmash-bio/sourmash_plugin_branchwater/pull/467/files#r1797783380

Implement TryInto<KmerMinHash> for Signature and SigStore to avoid having to clone a (potentially big) minhash sketch.

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codecov bot commented Oct 12, 2024

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.39%. Comparing base (62f03eb) to head (48d99c5).
Report is 1 commits behind head on refactor_rs_downsample.

Additional details and impacted files
@@                    Coverage Diff                     @@
##           refactor_rs_downsample    #3348      +/-   ##
==========================================================
+ Coverage                   86.48%   92.39%   +5.90%     
==========================================================
  Files                         137      104      -33     
  Lines                       16060    12909    -3151     
  Branches                     2215     2215              
==========================================================
- Hits                        13890    11927    -1963     
+ Misses                       1863      675    -1188     
  Partials                      307      307              
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@ctb ctb merged commit ff4eeda into refactor_rs_downsample Oct 13, 2024
35 of 43 checks passed
@ctb ctb deleted the lirber/try_into_minhash branch October 13, 2024 11:15
ctb added a commit that referenced this pull request Oct 15, 2024
…ather` bug around `scaled`. (#3342)

This PR does five things:

First, it swaps the implementation of `KmerMinHash::downsample_max_hash`
with `KmerMinHash::downsample_scaled`, and the same for
`KmerMinHashBTree`. Previously a call to `downsample_scaled` calculated
the right `max_hash` from `scaled`, then called `downsample_max_hash`,
which then converted `max_hash` back to `scaled`. This reverses the
logic so that (slightly) less work is done and, more importantly, the
code is a bit more straightforward.

Second, it changes the `downsample_*` functions so that they do not
downsample when no downsampling is needed. As part of this the method
signatures are changed to take an object, rather than a reference. This
lets the functions return an unmodified `KmerMinHash` when no
downsampling is needed.

Third, it turns out the `downsample_*` functions didn't check to make
sure that the new `scaled` value was larger than the old one, i.e. they
didn't prevent upsampling. That check was added and a new error,
`CannotUpsampleScaled`, was added to sourmash core.

Fourth, this uncovered a bug in `RevIndex::gather` where the query was
downsampled to the match, even when the match was lower scaled. This PR
rejiggers the code so that downsampling is done appropriately in the
`gather` and `calculate_gather_stats`. Since `RevIndex::gather` isn't
used in the the sourmash CLI, the bug only presented in the test suite
and in the branchwater plugin; see
sourmash-bio/sourmash_plugin_branchwater#468
and
sourmash-bio/sourmash_plugin_branchwater#467,
where a fastmultigather test had to be fixed because of the incorrect
scaled values output by `RevIndex::gather`.

Fifth, it includes #3348
from @luizirber, which adds a `Signature::try_into()` to `KmerMinHash`
to support the elimination of some clones.

Because of the method signature change for the `downsample_*` functions,
the sourmash-core version needs to be bumped to a new major version,
0.16.0.

It's been a fun journey! 😅 

Fixes #3343

Some notes on further changes and performance implications:

As a consequence of the `RevIndex::gather` changes, redundant
downsampling has to be done in `RevIndex::gather` and
`calculate_gather_stats`, unless we want to change the method signature
of `calculate_gather_stats`. I decided the PR was big enough that I
didn't want to do that in addition. It should not affect most use cases
where `scaled` is the same, and we will see if it results in any
slowdowns over in the branchwater plugin. See
#3196 for an issue on all
of this.

We could also just insist that the query scaled is the one to pay
attention to, per #2951.
This would simplify the code in Python-land as well.

Overall, the performance implications of this PR are not clear.
Previously downsampling was being done even when it wasn't needed, so
this may speed things up quite a lot for our typical use case! On the
other hand, redundant downsampling will happen in cases where there are
scaled mismatches. We just need to benchmark it, I think.

Some preliminary benchmarking reported in
sourmash-bio/sourmash_plugin_branchwater#430 (comment)
suggests that fastgather is now much more memory effficient 🎉 so that's
good!

TODO:
- [x] resolve the scaled mismatch stuff. do we return an `Err` or what
if the downsampling can't be performed?
- [x] update PR description
- [x] add more tests for downsampling, and maybe for gather
- [x] play with this code over in the branchwater plugin too!
sourmash-bio/sourmash_plugin_branchwater#467

---------

Co-authored-by: Luiz Irber <[email protected]>
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2 participants