[jira] [Work started] (ARTEMIS-3049) Reduce live page lookup cost

["Francesco Nigro (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARTEMIS-3049?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Work on ARTEMIS-3049 started by Francesco Nigro.
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> Reduce live page lookup cost
> ----------------------------
>
>                 Key: ARTEMIS-3049
>                 URL: https://issues.apache.org/jira/browse/ARTEMIS-3049
>             Project: ActiveMQ Artemis
>          Issue Type: Improvement
>          Components: Broker
>    Affects Versions: 2.16.0
>            Reporter: Francesco Nigro
>            Assignee: Francesco Nigro
>            Priority: Major
>          Time Spent: 1.5h
>  Remaining Estimate: 0h
>
> LivePageCacheImpl::getMessage is performing a linked-list-like lookup that can be rather slow if compared to an array lookup.
> [https://github.com/apache/activemq-artemis/pull/2494#issuecomment-455086939] clearly show the issue with the current implementation.
> The ideal approaches to improve it could be:
>  # to replace the chunked list with a copy on write array list
>  # to use cursor/iterator API over the chunk list, binding one to each consumer, in order to get a linear stride over the live paged messages
> Sadly, the latter approach seems not doable because the live page cache is accessed for each message lookup in an anonymous way, making impossible to have a 1:1 binding with the consumers, while the former seems not doable, because of the array copy cost on appending.
>  
> There is still one case that could be improved using the former approach, instead, delivering a huge speedup on lookup cost: reloading of live page.
> A reloaded live page already knows the amount of the loaded live paged messages, making possible to store them in a simple array.
>  



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