Introduce file system and implement streaming encoding

Signed-off-by: tabokie xy.tao@outlook.com

This PR rearranges internal data access around a standard reader/writer. This way external IO logic can be embedded through the new interface FileSystem, which allows for building wrapper around said reader/writer. This interface is not ideal as it doesn't ensure implementation to actually leverage the raw IO object. More work needs to be done to factor out code dependence on LogFd and sever FileSystem as a standalone abstraction.

This PR also implements streaming encoding. LogBatch now encodes user data immediately instead of keeping a copy and encode before actual writing.

Stress results:

Master:
- Thread 1
[write]
Throughput(QPS) = 8004.80
Latency(μs) min = 70, avg = 116.66, p50 = 112, p90 = 143, p95 = 156, p99 = 204, p99.9 = 497, max = 3997
Fairness = 100.0%
Write Bandwidth = 5.9MiB/s
- Thread 2
[write]
Throughput(QPS) = 17403.63
Latency(μs) min = 61, avg = 107.43, p50 = 102, p90 = 129, p95 = 143, p99 = 189, p99.9 = 406, max = 3653
Fairness = 100.0%
Write Bandwidth = 13.0MiB/s
- Thread 4
[write]
Throughput(QPS) = 30859.47
Latency(μs) min = 63, avg = 122.39, p50 = 114, p90 = 150, p95 = 167, p99 = 324, p99.9 = 581, max = 6083
Fairness = 99.7%
Write Bandwidth = 23.1MiB/s
- Thread 8
[write]
Throughput(QPS) = 47897.03
Latency(μs) min = 67, avg = 160.13, p50 = 154, p90 = 216, p95 = 237, p99 = 299, p99.9 = 675, max = 4987
Fairness = 99.5%
Write Bandwidth = 35.7MiB/s
- Thread 16
[write]
Throughput(QPS) = 52373.21
Latency(μs) min = 70, avg = 298.32, p50 = 288, p90 = 440, p95 = 517, p99 = 729, p99.9 = 1236, max = 11711
Fairness = 99.3%
Write Bandwidth = 39.2MiB/s

Patched:
- Thread 1
[write]
Throughput(QPS) = 8918.95
Latency(μs) min = 53, avg = 91.23, p50 = 88, p90 = 113, p95 = 122, p99 = 156, p99.9 = 387, max = 6179
Fairness = 100.0%
Write Bandwidth = 6.6MiB/s
- Thread 2
[write]
Throughput(QPS) = 19137.79
Latency(μs) min = 46, avg = 85.84, p50 = 82, p90 = 103, p95 = 115, p99 = 147, p99.9 = 362, max = 4955
Fairness = 100.0%
Write Bandwidth = 14.2MiB/s
- Thread 4
[write]
Throughput(QPS) = 34229.31
Latency(μs) min = 48, avg = 98.22, p50 = 95, p90 = 121, p95 = 133, p99 = 168, p99.9 = 443, max = 8055
Fairness = 99.9%
Write Bandwidth = 25.6MiB/s
- Thread 8
[write]
Throughput(QPS) = 50313.45
Latency(μs) min = 49, avg = 140.74, p50 = 134, p90 = 197, p95 = 218, p99 = 278, p99.9 = 733, max = 6119
Fairness = 99.5%
Write Bandwidth = 37.7MiB/s
- Thread 16
[write]
Throughput(QPS) = 54520.49
Latency(μs) min = 55, avg = 274.42, p50 = 268, p90 = 406, p95 = 477, p99 = 650, p99.9 = 1113, max = 18015
Fairness = 99.7%
Write Bandwidth = 40.7MiB/s

tikv / raft-engine

Introduce file system and implement streaming encoding #91