adriangb commented on code in PR #24165:
URL: https://github.com/apache/datafusion/pull/24165#discussion_r3737770315
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datafusion/proto-models/src/generated/prost.rs:
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@@ -2029,6 +2029,15 @@ pub struct HashJoinExecNode {
/// Optional dynamic filter expression for pushing down to the probe side.
#[prost(message, optional, tag = "11")]
pub dynamic_filter: ::core::option::Option<PhysicalExprNode>,
+ /// Optional row limit pushed into the join by the `limit_pushdown` rule.
+ ///
+ /// This is presence-tracked (`optional`) on purpose: messages produced by
+ /// versions predating this field carry no `fetch` at all, and a plain
proto3
+ /// scalar would decode that absence as `0`, i.e. "fetch 0 rows", silently
+ /// turning old plans into empty results. With `optional`, absent decodes
to
+ /// `None`, which is the correct reading of an older message.
+ #[prost(uint64, optional, tag = "12")]
+ pub fetch: ::core::option::Option<u64>,
Review Comment:
Yes, it will. Downstream code building HashJoinExecNode with an exhaustive
struct literal will need a new field. In practice prost's Message derive
supplies a Default impl, so the `..Default::default()` form is unaffected;
that's the idiom used in-tree too:
https://github.com/apache/datafusion/blob/92f4e8f3eeb7b8426399063b4226a591d0c062b3/datafusion/proto/src/physical_plan/mod.rs#L1371-L1377
This is also the established way these messages evolve — HashJoinExecNode
has gained a field four times already: projection (#9236), null_equality
(#16419), null_aware (#19635) and dynamic_filter (#22011). Short of never
adding fields, there isn't a mechanism that avoids it.
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