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https://issues.apache.org/jira/browse/CASSANDRA-8729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14305348#comment-14305348
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Joshua McKenzie commented on CASSANDRA-8729:
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While testing for CASSANDRA-6890 (debating removing mmap path), it was pretty
clear from my testing that mmap'ed I/O on Windows has a considerable advantage
over buffered to a degree that linux does not. I'm of the opinion we should
make efforts to memory-map our I/O on Windows wherever possible, with the known
caveat that it makes deleting and renaming files more complicated (all segments
have to be unmapped before either of those ops).
> 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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