comphead commented on code in PR #10501: URL: https://github.com/apache/datafusion/pull/10501#discussion_r1601777537
########## datafusion/optimizer/src/push_down_limit.rs: ########## @@ -217,6 +183,78 @@ impl OptimizerRule for PushDownLimit { } } +/// Combines two limits into a single +/// +/// Returns the combined limit `(skip, fetch)` +/// +/// # Case 0: Parent and Child are disjoint. (`child_fetch <= skip`) +/// +/// ```text +/// Before merging: +/// |........skip........|---fetch-->| Parent Limit +/// |...child_skip...|---child_fetch-->| Child Limit +/// ``` +/// +/// After merging: +/// ```text +/// |.........(child_skip + skip).........| +/// ``` +/// +/// Before merging: +/// ```text +/// |...skip...|------------fetch------------>| Parent Limit +/// |...child_skip...|-------------child_fetch------------>| Child Limit +/// ``` +/// +/// After merging: +/// ```text +/// |....(child_skip + skip)....|---(child_fetch - skip)-->| +/// ``` +/// +/// # Case 1: Parent is beyond the range of Child. (`skip < child_fetch <= skip + fetch`) +/// +/// Before merging: +/// ```text +/// |...skip...|------------fetch------------>| Parent Limit +/// |...child_skip...|-------------child_fetch------------>| Child Limit +/// ``` +/// +/// After merging: +/// ```text +/// |....(child_skip + skip)....|---(child_fetch - skip)-->| +/// ``` +/// +/// # Case 2: Parent is in the range of Child. (`skip + fetch < child_fetch`) +/// Before merging: +/// ```text +/// |...skip...|---fetch-->| Parent Limit +/// |...child_skip...|-------------child_fetch------------>| Child Limit +/// ``` +/// +/// After merging: +/// ```text +/// |....(child_skip + skip)....|---fetch-->| +/// ``` +fn combine_limit( + parent_skip: usize, + parent_fetch: Option<usize>, + child_skip: usize, + child_fetch: Option<usize>, +) -> (usize, Option<usize>) { + let combined_skip = child_skip + parent_skip; Review Comment: ```suggestion let combined_skip = child_skip.saturating_add(parent_skip); ``` -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: github-unsubscr...@datafusion.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: github-unsubscr...@datafusion.apache.org For additional commands, e-mail: github-h...@datafusion.apache.org