2010YOUY01 commented on code in PR #17467:
URL: https://github.com/apache/datafusion/pull/17467#discussion_r2329222755
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datafusion/common/src/config.rs:
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@@ -822,9 +822,34 @@ config_namespace! {
/// process to reorder the join keys
pub top_down_join_key_reordering: bool, default = true
- /// When set to true, the physical plan optimizer will prefer HashJoin
over SortMergeJoin.
+ /// When set to true, the physical plan optimizer will prefer HashJoin
when applicable.
+ /// If there are multiple preferred and applicable join types, the
optimizer
+ /// will choose one based on heuristics.
/// HashJoin can work more efficiently than SortMergeJoin but consumes
more memory
- pub prefer_hash_join: bool, default = true
+ pub prefer_hash_join: bool, default = false
Review Comment:
It's not a breaking change. By default there is no join types preferred, and
the planner will prioritize HJ according to heuristics, setting it to `true`
will just override the planner's default behavior.
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