[jira] [Commented] (CASSANDRA-15390) Avoid unnecessary collection/iterator allocations during btree construction

["Benedict Elliott Smith (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-15390?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16967687#comment-16967687 ] 

Benedict Elliott Smith commented on CASSANDRA-15390:
----------------------------------------------------

I like the pattern.  It might be worth putting in some explanatory comments, about why these functions exist?

I'm not thrilled by the name "Getter" since that usually means a member function that returns a value, but I don't have a much better suggestion.  Perhaps {{IterateFunction}}?  Could also drop "get" as a prefix of the method name.

I wonder if there is any value in introducing a bulk {{nextAt}} method that can fetch into an array, for the leaf building mode.  We could fetch them all via arrayCopy, then loop over the array to invoke the {{UpdateFunction}} (conditionally on it not being no-op, even, since we seem to test this anyway already).

> Avoid unnecessary collection/iterator allocations during btree construction
> ---------------------------------------------------------------------------
>
>                 Key: CASSANDRA-15390
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15390
>             Project: Cassandra
>          Issue Type: Sub-task
>          Components: Local/Compaction
>            Reporter: Blake Eggleston
>            Assignee: Blake Eggleston
>            Priority: Normal
>             Fix For: 4.0
>
>
> A heavily used btree builder path does a lot of unnecessary conversions to and from collections and iterators. Adding dedicated support for Object[] reduces compaction garbage by up to 8.3%



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