It's really bad. The problem is that the swapping of pages is constantly stalling the main Redis thread, which is not built for parallelism. Redis is built around a single highly efficient thread, so stalling it for 250us to pull a page from disk instantly reduces the throughput by an order of magnitude.
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How bad is Redis with a swap file on SSD?
I would expect it to be a very reasonable middle ground that requires almost no work and it is already enough and ready for most use cases.
It's really bad. The problem is that the swapping of pages is constantly stalling the main Redis thread, which is not built for parallelism. Redis is built around a single highly efficient thread, so stalling it for 250us to pull a page from disk instantly reduces the throughput by an order of magnitude.