本文属于机器翻译版本。若本译文内容与英语原文存在差异，则一律以英文原文为准。

# $change StreamSplitLargeEvent
<a name="changeStreamSplitLargeEvent"></a>

弹性集群不支持此聚合阶段。

此阶段从亚马逊文档数据库引擎版本 8.0.2 开始可用。

`$changeStreamSplitLargeEvent`聚合阶段在 $ChangeStream 管道中用于将超过 16 MB 的事件拆分为较小的片段。它通过变更流光标按顺序返回每个片段。

**参数**

无。`$changeStreamSplitLargeEvent`舞台的输入应为空文档。

## 示例 — MongoDB 外壳
<a name="changeStreamSplitLargeEvent-examples"></a>

以下示例演示使用`$changeStreamSplitLargeEvent`舞台将超大变更事件拆分为多个片段。

**查询示例 **

```
// Insert a document
db.inventory.insertOne({ _id: 1, item: "Widget", payload: "x".repeat(9 * 1024 * 1024) })

// Open change stream with the $changeStreamSplitLargeEvent stage
var changeStream = db.inventory.aggregate([
  { $changeStream: { fullDocument: "updateLookup" } },
  { $changeStreamSplitLargeEvent: {} }
]);

// Update the document
db.inventory.updateOne({ _id: 1 }, { $set: { payload: "y".repeat(9 * 1024 * 1024) } })

// Read the change event
if (changeStream.hasNext()) {
  print(tojson(changeStream.next()));
}
```

**输出**

```
{
  _id: { _data: '...' },
  splitEvent: { fragment: 1, of: 2},
  ns: { db: 'test', coll: 'inventory' },
  clusterTime: Timestamp(4, 1789154779),
  documentKey: { _id: 1 },
  fullDocument: { _id: 1, item: 'Widget', payload: yyyyyyyy...(9437184 chars) },
  operationType: 'update',
}
{
  _id: { _data: '...' },
  splitEvent: { fragment: 2, of: 2},
  updateDescription: { updatedFields: { payload: yyyyyyyy...(9437184 chars) }, removedFields: [] }
}
```

## 代码示例
<a name="changeStreamSplitLargeEvent-code"></a>

要查看使用`$changeStreamSplitLargeEvent`聚合阶段的代码示例，请选择要使用的语言的选项卡：

------
#### [ Node.js ]

```
const { MongoClient } = require('mongodb');

async function example() {
  const client = await MongoClient.connect('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');
  const db = client.db('test');
  const collection = db.collection('inventory');

  // Insert a large document first
  await collection.insertOne({ _id: 1, item: 'Widget', payload: 'x'.repeat(9 * 1024 * 1024) });

  // Open change stream with $changeStreamSplitLargeEvent
  const changeStream = collection.watch(
    [{ $changeStreamSplitLargeEvent: {} }],
    { fullDocument: 'updateLookup' }
  );

  changeStream.on('change', (change) => {
    console.log('Change detected:', change);
  });

  // Update to trigger a split event — fullDocument + updateDescription > 16 MB
  setTimeout(async () => {
    console.log('Triggering update...');
    await collection.updateOne({ _id: 1 }, { $set: { payload: 'y'.repeat(9 * 1024 * 1024) } });
  }, 1000);

  // Keep connection open to receive changes
  // In production, handle cleanup appropriately
}

example();
```

------
#### [ Python ]

```
from pymongo import MongoClient
import threading
import time

def example():
    client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
    db = client['test']
    collection = db['inventory']

    # Insert large document first
    collection.drop()
    collection.insert_one({'_id': 1, 'item': 'Widget', 'payload': 'x' * (9 * 1024 * 1024)})

    # Open change stream with $changeStreamSplitLargeEvent
    change_stream = collection.watch(
        [{'$changeStreamSplitLargeEvent': {}}],
        full_document='updateLookup'
    )

    # Update in separate thread after delay
    def update_doc():
        collection.update_one({'_id': 1}, {'$set': {'payload': 'y' * (9 * 1024 * 1024)}})

    threading.Thread(target=update_doc).start()

    # Watch for changes
    for change in change_stream:
        print('Change detected:', change)

    client.close()

example()
```

------