[jira] [Commented] (CASSANDRA-15765) Get-by-index introduced in CASSANDRA-15394 could have negative performance impact on non-RandomAccess List

["David Capwell (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-15765?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17093976#comment-17093976 ] 

David Capwell commented on CASSANDRA-15765:
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is there a code path you are seeing which doesn't use a list which supports random access?  Is this a potential performance issue or a monitored issue (and if so under which code path)?

> Get-by-index introduced in CASSANDRA-15394 could have negative performance impact on non-RandomAccess List
> ----------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-15765
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15765
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Legacy/Core
>            Reporter: Yifan Cai
>            Assignee: Yifan Cai
>            Priority: Normal
>
> CASSANDRA-15394 replaced the iterator based iteration with the get-by-index one to avoid allocation iterators. 
> It works for the lists that support RandomAccess, i.e. the big O of {{get()}} is {{O(1)}}. 
> However, it fails when the list does not support RandomAccess. The {{get()}} method's time complexity can be linear, and it leads to {{O(n^2)}} for the overall iteration. 
> The implementation should provide different behaviors based on the property. 



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