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A step between RAM and SSD could be "Your data fits in RAM in compressed form". LZ4 compression is takes 3-4x longer than memcpy. LZ4 decompression is only 50% [1] slower. 2-3 GB/s per core.

[1]: Your mileage may vary.

If it's slower both in and out what's the benefit?

To guy below me: Ah, thanks. I thought the guy above was trying to say it's slower than paging to disk. : )

Basically, parsing the percentages, using compressed data in RAM is ~1 order of magnitude slower to get into memory, and less than 1 order of magnitude slower to read from RAM. That is still around 2 (or more depending on setup) orders of magnitude faster than the hit to go to SSD / SSD RAID.

Useful knowledge on latency: https://gist.github.com/jboner/2841832

Because it's so much faster than having to go to disk.

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