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https://issues.apache.org/jira/browse/CASSANDRA-8729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14312799#comment-14312799
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T Jake Luciani commented on CASSANDRA-8729:
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I've been testing on low memory high cpu machines and have found this as a
potential major issue.
In a write heavy workload when mmapped data > ram I think there is a massive
number of page faults when writing to the CL and causes writes to stall and
spin out of control. Is there any workaround here? When I disable CL on the
same system the issues go away which makes me think it's this issue.
> 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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