Avoid the sort scratch allocation in NegentropyStorageVector::seal - #13
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Avoid the sort scratch allocation in NegentropyStorageVector::seal#13JSKitty wants to merge 1 commit into
NegentropyStorageVector::seal#13JSKitty wants to merge 1 commit into
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`Vec::sort` is a stable sort, and allocates a scratch buffer proportional
to the slice. For a 100,000-item store that is a transient 3.9 MB, which
doubles the peak memory of building a client store.
`Item` orders on timestamp then id, so two elements comparing equal are
byte-identical, and `dedup()` on the next line discards one of them
either way. Stability is unobservable here, so `sort_unstable` produces
the same sealed contents without the allocation.
Measured while sealing a 100,000-item store:
peak heap 7812 KB -> 3906 KB
transient 3906 KB -> 0 KB
The removed transient is exactly `100_000 * size_of::<Item>()`. Runtime is
unchanged within measurement noise.
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Vec::sortis a stable sort, and allocates a scratch buffer proportional to the slice. For a 100,000-item store that is a transient 3.9 MB, which doubles the peak memory of building a client store.Itemorders on timestamp then id, so two elements comparing equal are byte-identical, anddedup()on the next line discards one of them either way. Stability is unobservable here, sosort_unstableproduces the same sealed contents without the allocation.Measured while sealing a 100,000-item store:
The removed transient is exactly
100_000 * size_of::<Item>(). Runtime is unchanged within measurement noise.make precommitbefore committing