HappenLee opened a new issue #5985:
URL: https://github.com/apache/incubator-doris/issues/5985


   ## Motivation
   
   What's `parallal hash map`: https://greg7mdp.github.io/parallel-hashmap/
   
   * Very efficient, significantly faster than your compiler's unordered 
map/set or Boost's, or than sparsepp
   
   * Memory friendly: low memory usage, although a little higher than sparsepp
   
   * Supports heterogeneous lookup
   
   So, We Should Use Parallel Hash Map Replace Unordered Map in Hotspot Code 
Path
   
   
   ## Test
   
   1000w data use `in expr` in varchar in (`1` ~ `1025`), because `parallal 
hash map` Support `heterogeneous lookup` which can greatly reduce memory alloc 
for `HyperSet<StringValue>`.
   
   | Underordered Map | Parallel Hash Map|
   | :-----: | :----: |
   | 2.3s | 1.49s |


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