[jira] [Updated] (CASSANDRA-8729) Commitlog causes read before write when overwriting

["T Jake Luciani (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-8729?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

T Jake Luciani updated CASSANDRA-8729:
--------------------------------------
    Reproduced In: 2.1.2

> Commitlog causes read before write when overwriting
> ---------------------------------------------------
>
>                 Key: CASSANDRA-8729
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8729
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Ariel Weisberg
>
> The memory mapped commit log implementation writes directly to the page cache. If a page is not in the cache the kernel will read it in even though we are going to overwrite.
> The way to avoid this is to write to private memory, and then pad the write with 0s at the end so it is page (4k) aligned before writing to a file.
> The commit log would benefit from being refactored into something that looks more like a pipeline with incoming requests receiving private memory to write in, completed buffers being submitted to a  parallelized compression/checksum step, followed by submission to another thread for writing to a file that preserves the order.



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