adriangb commented on issue #20195:
URL: https://github.com/apache/datafusion/issues/20195#issuecomment-4164457702

   > [@gene-bordegaray](https://github.com/gene-bordegaray) asked me in the 
meeting why a CASE + hash was decided to route dynamic filters, 
[@adriangb](https://github.com/adriangb) you might remember better than me, but 
I think it was to avoid keeping a hash table with partition info + the whole 
build side hash table (which could cause memory issues). There were some 
discussions 
[here](https://github.com/apache/datafusion/pull/17529#discussion_r2353830615) 
and 
[here](https://github.com/apache/datafusion/issues/17171#issuecomment-3313002604)
   
   I guess the question depends on what the alternative is. As far as I can 
remember / think of the two alternatives would be to try every partition's hash 
table (poor build side performance and questionable probe side performance) or 
to make a combined hash table with all values (poor memory use).


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