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T Jake Luciani commented on CASSANDRA-8729: ------------------------------------------- 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. -- This message was sent by Atlassian JIRA (v6.3.4#6332)