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https://issues.apache.org/jira/browse/ARROW-2798?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Philipp Moritz reassigned ARROW-2798:
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Assignee: Songqing Zhang
> [Plasma] Use hashing function that takes into account all UniqueID bytes
> ------------------------------------------------------------------------
>
> Key: ARROW-2798
> URL: https://issues.apache.org/jira/browse/ARROW-2798
> Project: Apache Arrow
> Issue Type: Improvement
> Components: Plasma (C++)
> Affects Versions: 0.9.0
> Reporter: Songqing Zhang
> Assignee: Songqing Zhang
> Priority: Major
> Labels: performance, pull-request-available
> Fix For: 0.10.0
>
> Time Spent: 1h 10m
> Remaining Estimate: 0h
>
> Now, the hashing of UniqueID in plasma is too simple which has caused a
> problem. In some cases(for example, in github/ray, UniqueID is composed of a
> taskID and a index), the UniqueID may be like "ffffffffffffffffffff00",
> "ffffffffffffffffff01", "fffffffffffffffffff02" ... . The current hashing
> method is only to copy the first few bytes of a UniqueID and the result is
> that most of the hashed ids are same, so when the hashed ids put to plasma
> store, it will become very slow when searching(plasma store uses
> unordered_map to store the ids, and when the keys are same, it will become
> slow just like list).
> I have submitted a PR to solve the problem, see
> [https://github.com/apache/arrow/pull/2220] .In fact, the same PR has been
> merged into ray, see
> [ray-project/ray#2174|https://github.com/ray-project/ray/pull/2174].
> and I have tested the perf between the new hashing method and the original
> one with putting lots of objects continuously, it seems the new hashing
> method doesn't cost more time.
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