rtpsw commented on code in PR #34392:
URL: https://github.com/apache/arrow/pull/34392#discussion_r1195522221
##########
cpp/src/arrow/acero/asof_join_node.cc:
##########
@@ -704,21 +846,27 @@ class InputState {
Rehash();
}
memo_.Store(ts, rb, latest_ref_row_, latest_time, GetLatestKey());
+ // negative tolerance means a last-known entry was stored - set
`updated` to `true`
updated = memo_.no_future_;
ARROW_ASSIGN_OR_RAISE(advanced, Advance());
} while (advanced);
- if (!memo_.no_future_) { // "updated" was not modified in the loop; set
it here
+ if (!memo_.no_future_ && latest_time >= ts) {
Review Comment:
This is where the exposed `latest_time` is used. If `latest_time` is less
than `ts` then we know upfront that `updated =
memo_.RemoveEntriesWithLesserTime(ts);` would have no effect, since all entries
would have time no greater than `latest_time` and hence less than `ts`. This is
an optimization.
##########
cpp/src/arrow/acero/asof_join_node.cc:
##########
@@ -704,21 +846,27 @@ class InputState {
Rehash();
}
memo_.Store(ts, rb, latest_ref_row_, latest_time, GetLatestKey());
+ // negative tolerance means a last-known entry was stored - set
`updated` to `true`
updated = memo_.no_future_;
ARROW_ASSIGN_OR_RAISE(advanced, Advance());
} while (advanced);
- if (!memo_.no_future_) { // "updated" was not modified in the loop; set
it here
+ if (!memo_.no_future_ && latest_time >= ts) {
Review Comment:
This is where the exposed `latest_time` is used. If `latest_time` is less
than `ts` then we know upfront that `updated =
memo_.RemoveEntriesWithLesserTime(ts);` would have no effect, since all entries
would have time no greater than `latest_time` and hence less than `ts`. This is
a small optimization.
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