[ARROW-2798] [Plasma] Use hashing function that takes into account all UniqueID bytes

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.9.0
• Fix Version/s: 0.10.0
• Component/s: C++ - Plasma
• Labels: performance pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/19179
• Assignee: Songqing Zhang
• Reporter: Songqing Zhang
• Created: 06/Jul/18 07:33
• Updated: 11/Jan/23 07:23
• Resolved: 06/Jul/18 20:51

Description

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.

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.

Issue Links

• links to: GitHub Pull Request #2220