add timelines for slow log

[iosmanthus]

Feature Request

Is your feature request related to a problem? Please describe:
For now, the format of the slow log is hard to read and comprehend.

{
    "start": "15:35:31.156",
    "end": "15:35:32.733",
    "duration": "1577ms",
    "func": "get",
    "key": "indexInfo_:_pf01_:_APD01_:_0202250000062470157",
    "spans": [
        {
            "name": "callWithRetry pdpb.PD/GetStore",
            "start": "15:35:31.156",
            "end": "15:35:31.623",
            "duration": "467ms"
        },
        {
            "name": "gRPC pdpb.PD/GetStore",
            "start": "15:35:31.156",
            "end": "15:35:31.156",
            "duration": "0ms"
        },
        {
            "name": "backoff BoPDRPC",
            "start": "15:35:31.156",
            "end": "15:35:31.239",
            "duration": "83ms"
        },
        {
            "name": "gRPC pdpb.PD/GetStore",
            "start": "15:35:31.240",
            "end": "15:35:31.240",
            "duration": "0ms"
        },
        {
            "name": "backoff BoPDRPC",
            "start": "15:35:31.240",
            "end": "15:35:31.375",
            "duration": "135ms"
        },
        {
            "name": "gRPC pdpb.PD/GetStore",
            "start": "15:35:31.376",
            "end": "15:35:31.376",
            "duration": "0ms"
        },
        {
            "name": "backoff BoPDRPC",
            "start": "15:35:31.376",
            "end": "15:35:31.622",
            "duration": "246ms"
        },
        {
            "name": "gRPC pdpb.PD/GetStore",
            "start": "15:35:31.622",
            "end": "15:35:31.622",
            "duration": "0ms"
        },
        {
            "name": "backoff BoPDRPC",
            "start": "15:35:31.622",
            "end": "N/A",
            "duration": "N/A"
        },
        {
            "name": "backoff BoRegionMiss",
            "start": "15:35:31.623",
            "end": "15:35:31.643",
            "duration": "20ms"
        },
        ...
    ]
}

However, the timeline graph will be more illustrated:

Describe the feature you'd like:
Add a tool to produce a simple timeline graph while given a log file.

Describe alternatives you've considered:
Use tracing for the future, slow log can't trace the event relationship.

Teachability, Documentation, Adoption, Migration Strategy:

[zz-jason]

compared with a timeline tool to be displayed in the terminal, maybe a better replacement is a request stats which can analyze the grpc and backoff total time and order all the items in a specific order like the following:

the python script

#!/usr/bin/env python3
#!coding:utf-8

import re
import json
import argparse

def main():
    pattern = r'.*SlowLog.*'
    slowstr = "SlowLog:"

    args = parse_args()
    items = []
    with open(args.slowlog, encoding = 'utf-8') as f:
        for line in f.readlines():
            matched = re.match(pattern, line, re.M|re.I)
            if matched is not None:
                log = json.loads(line[(line.index(slowstr) + len(slowstr)):])
                item = {
                    'req': log['func'],
                    'start': log['start'],
                    'total latency': int(log['duration'][:len(log['duration'])-2]),
                    'total grpc latency': 0,
                    'total backoff latency': 0,
                }
                for span in log['spans']:
                    if 'gRPC tikvpb.Tikv' in span['name'] and span['duration'] != 'N/A':
                        item['total grpc latency'] += int(span['duration'][:len(span['duration'])-2])
                    if 'backoff ' in span['name'] and span['duration'] != 'N/A':
                        item['total backoff latency'] += int(span['duration'][:len(span['duration'])-2])

                items.append(item)

        if args.order == "total":
            items = sorted(items, key=lambda d: d['total latency'], reverse=True)
        elif args.order == "grpc":
            items = sorted(items, key=lambda d: d['total grpc latency'], reverse=True)
        elif args.order == "backoff":
            items = sorted(items, key=lambda d: d['total backoff latency'], reverse=True)
        else:
            print("unsupported order field, use default value: total")
            items = sorted(items, key=lambda d: d['total latency'], reverse=True)

    fmtStr = "{:<12} {:<14} {:<14} {:<20} {:<20}"
    print(fmtStr.format("Request", "Start", "Total Lat(ms)", "Total gRPC Lat(ms)", "Total Backoff Lat(ms)"))
    for item in items:
        print(fmtStr.format(item['req'], item['start'], item['total latency'], item['total grpc latency'], item['total backoff latency']))

def parse_args():
    parser = argparse.ArgumentParser(description="rstats: A TiKV Java Client Request Stats Analyzer")
    parser.add_argument(
            "--slowlog",
            dest="slowlog",
            help="slowlog file, default: slow.log",
            default="slow.log")
    parser.add_argument(
            "--order",
            dest="order",
            help="sort the output, default: total. Accepted value: total, grpc, backoff",
            default="total")
    return parser.parse_args()

if __name__ == '__main__':
    main()

➜ ./rstat.py --order grpc
Request      Start          Total Lat(ms)  Total gRPC Lat(ms)   Total Backoff Lat(ms)
putIfAbsent  22:50:36.364   868            751                  116
putIfAbsent  22:50:36.945   625            571                  46
get          05:23:05.893   11             11                   0
putIfAbsent  05:23:10.665   23             0                    21