alamb opened a new issue #143:
URL: https://github.com/apache/arrow-datafusion/issues/143


   *Note*: migrated from original JIRA: 
https://issues.apache.org/jira/browse/ARROW-11116
   
   Currently, the left join implementation keeps a HashSet<Vec<u8>> to mark 
each key as visited.
   
   However, a more efficient choice would be to keep a bitmap or a boolean 
marker for each key or index and mark the row as visited, avoiding unnecessary 
hashing, copying / memory usage.
   
   This bitmap / marker can be visited at the end of the join, efficiently 
adding the remaining left rows with no match.


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