make cassandra io threads configurable #4034
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thejohnfreeman
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Dec 14, 2021
mtrippled
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This commit was authored by @cjcobb23 and has been running in our reporting environments.
High Level Overview of Change
The cassandra driver uses worker threads to process requests. The number of worker threads is configurable, though previously we just set it to
std::thread::hardware_concurrency. For large machines with many cores, this is probably too much. We noticed on the large machines that under high CPU load, a large majority of the CPU time was spent in system calls. Reducing the number of io threads used by the driver brought the amount of time spent in system calls down. This commit introduces a config option to set the number of io threads, and also changes the default to 4.