簡單理解skywalking資料上報的span概念

簡單理解

spanType總共有三種：

1. Entry：表示整個程式的span
2. Local：表示程式內部的處理，是EntrySpan的一部分
3. Exit：表示發起一個遠端呼叫，如請求db、redis，如發起http請求、rpc呼叫

spanLayer總共有六種（和jaeger不一樣，它以span.tags陣列key=component的值來分類）：

1. Unknown：未知
2. Database：請求db
3. RPCFramework：rpc呼叫
4. Http：發起http請求（或者本身是http服務）
5. MQ：訊息服務
6. Cache：快取服務

場景一：一個http請求，處理上傳和請求db，則建立三個span
spanId=0 parentSpanId=-1 spanType=entry spanLayer=http
spanId=1 parentSpanId= 0 spanType=local spanLayer=Unknown
spanId=2 parentSpanId= 0 spanType=exit spanLayer=database

場景二：一個http請求，有http請求，則建立兩個個span
spanId=0 parentSpanId=-1 spanType=entry spanLayer=http
spanId=1 parentSpanId= 0 spanType=exit spanLayer=http

場景三：一個http請求，有訪問redis。場景二的第2個span正是訪問的它。建立兩個span（其中traceId和場景二的traceId相等）
spanId=0 parentSpanId=-1 spanType=entry spanLayer=http refs=包含場景二中第2個span的資訊
spanId=1 parentSpanId= 0 spanType=exit spanLayer=cache

原始日誌

這裡記錄一下真實的trace日誌，來證實上面說的場景二和場景三

場景二

{
    "traceId": "6763beaf2ad8a9e4c05114b978a97072.17.756430259",
    "traceSegmentId": "6763beaf2ad8a9e4c05114b978a97072.17.756430259",
    "spans": [
        {
            "spanId": 0,
            "parentSpanId": -1,
            "startTime": "1639096358706",
            "endTime": "1639096359252",
            "refs": [],
            "operationName": "/answer4/activityStyle",
            "peer": "192.168.2.119:72",
            "spanType": "Entry",
            "spanLayer": "Http",
            "componentId": 8001,
            "isError": false,
            "tags": [
                {
                    "key": "url",
                    "value": "/answer4/activityStyle"
                },
                {
                    "key": "status_code",
                    "value": "200"
                }
            ],
            "logs": [],
            "skipAnalysis": false
        },
        {
            "spanId": 1,
            "parentSpanId": 0,
            "startTime": "1639096358775",
            "endTime": "1639096359250",
            "refs": [],
            "operationName": "/op/answer4/activityStyle",
            "peer": "container-ng9272:62",
            "spanType": "Exit",
            "spanLayer": "Http",
            "componentId": 8002,
            "isError": false,
            "tags": [
                {
                    "key": "url",
                    "value": "http://container-ng9272:62/op/answer4/activityStyle"
                },
                {
                    "key": "status_code",
                    "value": "200"
                }
            ],
            "logs": [],
            "skipAnalysis": false
        }
    ],
    "service": "op",
    "serviceInstance": "ca6185b0-752c-9aab-d9f9-6796da2c0646@172.18.0.5",
    "isSizeLimited": false
}

場景三

{
    "traceId": "6763beaf2ad8a9e4c05114b978a97072.17.756430259",
    "traceSegmentId": "6763beaf2ad8a9e4c05114b978a97072.18.4224945771",
    "spans": [
        {
            "spanId": 0,
            "parentSpanId": -1,
            "startTime": "1639096358782",
            "endTime": "1639096359250",
            "refs": [
                {
                    "refType": "CrossProcess",
                    "traceId": "6763beaf2ad8a9e4c05114b978a97072.17.756430259",
                    "parentTraceSegmentId": "6763beaf2ad8a9e4c05114b978a97072.17.756430259",
                    "parentSpanId": 1,
                    "parentService": "op",
                    "parentServiceInstance": "ca6185b0-752c-9aab-d9f9-6796da2c0646@172.18.0.5",
                    "parentEndpoint": "/answer4/activityStyle",
                    "networkAddressUsedAtPeer": "container-ng9272:62"
                }
            ],
            "operationName": "/op/answer4/activityStyle",
            "peer": "container-ng9272:62",
            "spanType": "Entry",
            "spanLayer": "Http",
            "componentId": 8001,
            "isError": false,
            "tags": [
                {
                    "key": "url",
                    "value": "/op/answer4/activityStyle"
                },
                {
                    "key": "status_code",
                    "value": "200"
                }
            ],
            "logs": [],
            "skipAnalysis": false
        },
        {
            "spanId": 1,
            "parentSpanId": 0,
            "startTime": "1639096358942",
            "endTime": "1639096358966",
            "refs": [],
            "operationName": "Redis->get",
            "peer": "localhost:6379",
            "spanType": "Exit",
            "spanLayer": "Cache",
            "componentId": 7,
            "isError": false,
            "tags": [
                {
                    "key": "db.type",
                    "value": "redis"
                },
                {
                    "key": "redis.command",
                    "value": "GET answer4:opdb"
                }
            ],
            "logs": [],
            "skipAnalysis": false
        }
    ],
    "service": "op",
    "serviceInstance": "ca6185b0-752c-9aab-d9f9-6796da2c0646@172.18.0.5",
    "isSizeLimited": false
}

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