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Resize with a more conservative amount of space after deletions #86

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merged 1 commit into from
Jun 6, 2019

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edre
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@edre edre commented Jun 4, 2019

Otherwise we can force a rehash for each insert and removal if we're right under the size limit.

Benchmark with SIZE=895, just under a rehash limit.
name oops ns/iter okthen ns/iter diff ns/iter diff % speedup
insert_erase_std_serial 9,875,585 60,696 -9,814,889 -99.39% x 162.71

Fixes #85

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Amanieu commented Jun 5, 2019

I think a better solution would be to change the else clause to

self.resize(usize::max(new_size, full_capacity + 1), hasher, fallability)

This ensures that we always increase the table size if we are resizing.

Also the condition should probably be changed from < to <= to match the original C++ version.

…deletions.

Otherwise we can force a rehash for each insert and removal if we're right under the size limit.

Benchmark with SIZE=895, just under a rehash limit.
    name                     oops ns/iter  okthen ns/iter  diff ns/iter   diff %   speedup
    insert_erase_std_serial  9,875,585     60,696            -9,814,889  -99.39%  x 162.71

Fixes rust-lang#85
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Amanieu commented Jun 6, 2019

@bors r+

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bors commented Jun 6, 2019

📌 Commit afc20d7 has been approved by Amanieu

bors added a commit that referenced this pull request Jun 6, 2019
Resize with a more conservative amount of space after deletions

Otherwise we can force a rehash for each insert and removal if we're right under the size limit.

Benchmark with SIZE=895, just under a rehash limit.
    name                     oops ns/iter  okthen ns/iter  diff ns/iter   diff %   speedup
    insert_erase_std_serial  9,875,585     60,696            -9,814,889  -99.39%  x 162.71

Fixes #85
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bors commented Jun 6, 2019

⌛ Testing commit afc20d7 with merge b240ee0...

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bors commented Jun 6, 2019

☀️ Test successful - checks-travis
Approved by: Amanieu
Pushing b240ee0 to master...

@bors bors merged commit afc20d7 into rust-lang:master Jun 6, 2019
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Frequent rehashes when size is close to capacity
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