我正在尝试遍历DynamoDB表中的所有项目. (我知道这是一个效率低下的过程,但我这样做是为了构建一个索引表.)

据我所知,DynamoDB的scan()函数返回1MB或提供的限制中的较小者.为了弥补这一点,我编写了一个函数来查找“LastEvaluatedKey”结果,并从LastEvaluatedKey开始重新查询以获取所有结果.

不幸的是,似乎每次我的函数循环,整个数据库中的每一个键都被扫描,快速耗尽我分配的读取单位.这非常慢.

这是我的代码：

def search(table,scan_filter=None,range_key=None,attributes_to_get=None,limit=None):
    """ Scan a database for values and return
        a dict.
    """

    start_key = None
    num_results = 0
    total_results = []
    loop_iterations = 0
    request_limit = limit

    while num_results < limit:
        results = self.conn.layer1.scan(table_name=table,attributes_to_get=attributes_to_get,exclusive_start_key=start_key,limit=request_limit)
        num_results = num_results + len(results['Items'])
        start_key = results['LastEvaluatedKey']
        total_results = total_results + results['Items']
        loop_iterations = loop_iterations + 1
        request_limit = request_limit - results['Count']

        print "Count: " + str(results['Count'])
        print "Scanned Count: " + str(results['ScannedCount'])
        print "Last Evaluated Key: " + str(results['LastEvaluatedKey']['HashKeyElement']['S'])
        print "Capacity: " + str(results['ConsumedCapacityUnits'])
        print "Loop Iterations: " + str(loop_iterations)

    return total_results

调用函数：

db = DB()
results = db.search(table='media',limit=500,attributes_to_get=['id'])

我的输出：

Count: 96
Scanned Count: 96
Last Evaluated Key: kBR23QJNAwYZZxF4E3N1crQuaTwjIeFfjIv8NyimI9o
Capacity: 517.5
Loop Iterations: 1
Count: 109
Scanned Count: 109
Last Evaluated Key: ATcJFKfY62NIjTYY24Z95Bd7xgeA1PLXAw3gH0KvUjY
Capacity: 516.5
Loop Iterations: 2
Count: 104
Scanned Count: 104
Last Evaluated Key: Lm3nHyW1KMXtMXNtOSpAi654DSpdwV7dnzezAxApAJg
Capacity: 516.0
Loop Iterations: 3
Count: 104
Scanned Count: 104
Last Evaluated Key: iirRBTPv9xDcqUVOAbntrmYB0PDRmn5MCDxdA6Nlpds
Capacity: 513.0
Loop Iterations: 4
Count: 100
Scanned Count: 100
Last Evaluated Key: nBUc1LHlPPELGifGuTSqPNfBxF9umymKjCCp7A7XWXY
Capacity: 516.5
Loop Iterations: 5

这是预期的行为吗？或者,我做错了什么？