zero-copy buffer reader -- slice buffer

[jeffreye]

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see also #2173

Here are some performance results

db.PIPELINE GET.requests - 10000 db.PIPELINE GET.size - 128 db.clients - 1 db.loop - 5 Loaded keys - 1918458 Connections Formed PIPELINE GET Performance Total Req - 1280000 P50 (ms) - 2.35 Avg (ms) - 2.6 P90 (ms) - 3.28 P95 (ms) - 3.81 P99 (ms) - 7.24 OPS - 49167 Time Taken (s) for loop 0 is - 26.95 PIPELINE GET Performance Total Req - 1280000 P50 (ms) - 2.3 Avg (ms) - 2.84 P90 (ms) - 3.12 P95 (ms) - 3.56 P99 (ms) - 6.65 OPS - 45027 Time Taken (s) for loop 1 is - 29.26 PIPELINE GET Performance Total Req - 1280000 P50 (ms) - 2.33 Avg (ms) - 2.52 P90 (ms) - 3.16 P95 (ms) - 3.55 P99 (ms) - 6.01 OPS - 50826 Time Taken (s) for loop 2 is - 25.97 PIPELINE GET Performance Total Req - 1280000 P50 (ms) - 2.32 Avg (ms) - 2.49 P90 (ms) - 3.13 P95 (ms) - 3.47 P99 (ms) - 5.8 OPS - 51426 Time Taken (s) for loop 3 is - 25.65 PIPELINE GET Performance Total Req - 1280000 P50 (ms) - 2.34 Avg (ms) - 2.54 P90 (ms) - 3.18 P95 (ms) - 3.65 P99 (ms) - 6.55 OPS - 50337 Time Taken (s) for loop 4 is - 26.2

db.PIPELINE GET.requests - 10000 db.PIPELINE GET.size - 128 db.clients - 1 db.loop - 5 Loaded keys - 1918458 Connections Formed PIPELINE GET Performance Total Req - 1280000 P50 (ms) - 1.81 Avg (ms) - 2.08 P90 (ms) - 2.55 P95 (ms) - 3.02 P99 (ms) - 6.02 OPS - 61661 Time Taken (s) for loop 0 is - 21.69 PIPELINE GET Performance Total Req - 1280000 P50 (ms) - 1.76 Avg (ms) - 1.93 P90 (ms) - 2.24 P95 (ms) - 2.56 P99 (ms) - 4.48 OPS - 66164 Time Taken (s) for loop 1 is - 20.18 PIPELINE GET Performance Total Req - 1280000 P50 (ms) - 1.77 Avg (ms) - 1.96 P90 (ms) - 2.28 P95 (ms) - 2.69 P99 (ms) - 5.2 OPS - 65170 Time Taken (s) for loop 2 is - 20.44 PIPELINE GET Performance Total Req - 1280000 P50 (ms) - 1.75 Avg (ms) - 1.93 P90 (ms) - 2.22 P95 (ms) - 2.57 P99 (ms) - 5.09 OPS - 66303 Time Taken (s) for loop 3 is - 20.07 PIPELINE GET Performance Total Req - 1280000 P50 (ms) - 1.77 Avg (ms) - 1.94 P90 (ms) - 2.25 P95 (ms) - 2.61 P99 (ms) - 4.81 OPS - 65856 Time Taken (s) for loop 4 is - 20.19