amazon-web-services - dynamodb中原子事务的实现

Question

我在 dynamodb 中有一个表，我需要一次更新多个相关项目(由于 400kb 大小限制，我无法将所有数据放在一个项目中)。
如何确保多行更新成功或无更新。

最终目标是在更新后读取一致的数据。

Answer 1

关于 November 27th, 2018, transactions for Dynamo DB were announced. 来自链接的文章:

DynamoDB transactions provide developers atomicity, consistency, isolation, and durability (ACID) across one or more tables within a single AWS account and region. You can use transactions when building applications that require coordinated inserts, deletes, or updates to multiple items as part of a single logical business operation. DynamoDB is the only non-relational database that supports transactions across multiple partitions and tables.

新的 API 是:

• TransactWriteItems, a batch operation that contains a write set, with one or more PutItem, UpdateItem, and DeleteItem operations. TransactWriteItems can optionally check for prerequisite conditions that must be satisfied before making updates. These conditions may involve the same or different items than those in the write set. If any condition is not met, the transaction is rejected.

• TransactGetItems, a batch operation that contains a read set, with one or more GetItem operations. If a TransactGetItems request is issued on an item that is part of an active write transaction, the read transaction is canceled. To get the previously committed value, you can use a standard read.

链接的文章还有一个 JavaScript 示例:

data = await dynamoDb.transactWriteItems({
  TransactItems: [
    {
      Update: {
        TableName: 'items',
        Key: { id: { S: itemId } },
        ConditionExpression: 'available = :true',
        UpdateExpression: 'set available = :false, ' +
            'ownedBy = :player',
        ExpressionAttributeValues: {
          ':true': { BOOL: true },
          ':false': { BOOL: false },
          ':player': { S: playerId }
        }
      }
    },
    {
      Update: {
        TableName: 'players',
        Key: { id: { S: playerId } },
        ConditionExpression: 'coins >= :price',
        UpdateExpression: 'set coins = coins - :price, ' +
            'inventory = list_append(inventory, :items)',
        ExpressionAttributeValues: {
          ':items': { L: [{ S: itemId }] },
          ':price': { N: itemPrice.toString() }
        }
      }
    }
  ]
}).promise();