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Example for parallelScanAsStream #266

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@robertkossendey

Hello,

I am running parallelScanAsStream to dump a whole DynamoDB table to S3. It is awfully slow though, slower than running sequential scan. Running it locally I am getting results like:

Config: {"concurrency":16,"chunkSize":1000,"highWaterMark":1000}
Total items: 167744, Duration: 92.73s
Throughput: 1808.91 items/second

Config: {"concurrency":32,"chunkSize":2000,"highWaterMark":2000}
Total items: 167744, Duration: 108.71s
Throughput: 1543.01 items/second

Config: {"concurrency":64,"chunkSize":5000,"highWaterMark":5000}
Total items: 167744, Duration: 109.73s
Throughput: 1528.67 items/second

My code looks the following:

const agent = new https.Agent({
    maxSockets: 100
});

const dynamodbClient = new DynamoDBClient({
    requestHandler: new NodeHttpHandler({
        httpsAgent: agent
    })
});

const stream = await parallelScanAsStream(
        { TableName: event.tableName },
        {
            concurrency: 100,
            chunkSize: 200,
            client: dynamodbClient
        }
    );

    for await (const items of stream) {
        const records = items.map((item: any) => {
            return {
                Data: Buffer.from(
                    JSON.stringify(item,
                        (_, v) => (typeof v === 'bigint' ? v.toString() : v)
                    ) + '\n'
                )
            };
        });

        await aysncProcessingFunction(records);
    }
}

The asyncProcessing function itself is not the problem.
Does anyone see something obvious that I am doing wrong? Or can someone provide me some examples?

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