Batch Insertion

Now if you have a massive amount of data to insert into Dynamo, I would suggest using an EMR data pipeline (theres even an example for exactly this). But if you stubborn, here is an example of inserting lots of items into Dynamo (it’s not really that complicated once you’ve read it).

What the code does is generates items (e.g. item0, item1, item2…) and writes them to a table “test” against a primary partition key called “pk” (with 5 read and 5 write units, no auto-scaling).

The batch_write_item method only takes a max of 25 items at a time, so the script computes 25 items, writes them, then does it all over again.

After Dynamo has had enough, it will start throttling you and return any items that have not been written in the response. Once the script is being throttled, it will start sleeping for 5 seconds until the failed items have been successfully written, after that it will exit.

# Boto should get credentials from ~/.aws/credentials or the environment
import asyncio

from aiobotocore.session import get_session


def get_items(start_num, num_items):
    """
    Generate a sequence of dynamo items

    :param start_num: Start index
    :type start_num: int
    :param num_items: Number of items
    :type num_items: int
    :return: List of dictionaries
    :rtype: list of dict
    """
    result = []
    for i in range(start_num, start_num+num_items):
        result.append({'pk': {'S': 'item{0}'.format(i)}})
    return result


def create_batch_write_structure(table_name, start_num, num_items):
    """
    Create item structure for passing to batch_write_item

    :param table_name: DynamoDB table name
    :type table_name: str
    :param start_num: Start index
    :type start_num: int
    :param num_items: Number of items
    :type num_items: int
    :return: dictionary of tables to write to
    :rtype: dict
    """
    return {
        table_name: [
            {'PutRequest': {'Item': item}}
            for item in get_items(start_num, num_items)
        ]
    }


async def go():
    session = get_session()
    async with session.create_client('dynamodb', region_name='us-west-2') as client:
        table_name = 'test'

        print('Writing to dynamo')
        start = 0
        while True:
            # Loop adding 25 items to dynamo at a time
            request_items = create_batch_write_structure(table_name, start, 25)
            response = await client.batch_write_item(
                RequestItems=request_items
            )
            if len(response['UnprocessedItems']) == 0:
                print('Wrote 25 items to dynamo')
            else:
                # Hit the provisioned write limit
                print('Hit write limit, backing off then retrying')
                await asyncio.sleep(5)

                # Items left over that haven't been inserted
                unprocessed_items = response['UnprocessedItems']
                print('Resubmitting items')
                # Loop until unprocessed items are written
                while len(unprocessed_items) > 0:
                    response = await client.batch_write_item(
                        RequestItems=unprocessed_items
                    )
                    # If any items are still left over, add them to the
                    # list to be written
                    unprocessed_items = response['UnprocessedItems']

                    # If there are items left over, we could do with
                    # sleeping some more
                    if len(unprocessed_items) > 0:
                        print('Backing off for 5 seconds')
                        await asyncio.sleep(5)

                # Inserted all the unprocessed items, exit loop
                print('Unprocessed items successfully inserted')
                break

            start += 25

        # See if DynamoDB has the last item we inserted
        final_item = 'item' + str(start + 24)
        print(f'Item "{final_item}" should exist')

        response = await client.get_item(
            TableName=table_name,
            Key={'pk': {'S': final_item}}
        )
        print(f'Response: {response["Item"]}')


if __name__ == '__main__':
    asyncio.run(go())