我应该如何构建我的 MongoDB 复合索引？

Question

我有一个由以下字段组成的 mongo 图像元数据集合：camera_name(str)、photographer_name(str)、resolution(str)、image_size(int in MB, rounded) 和 timestamp(10 digit UNIX timestamp)

我只想运行 2 个查询：

1. 给定 camera_name，返回时间戳 <= 1639457261 的记录（示例 UNIX 时间戳）。 记录必须按降序排序
2. 给定相机名称、摄影师名称、分辨率、图像大小和时间戳，我想检索记录，按输入的时间戳的降序排序。

我创建了 2 个索引：

1. { "camera_name": 1, "timestamp": -1 }
2. { "camera_name": 1, "photographer_name": 1, "resolution": 1, "image_size": 1, "timestamp": -1}

第一个索引有效，但是当我对第二个索引运行查询时，没有返回任何记录。 我确信集合中存在记录，并且我希望在运行第二个查询时至少获得 10 条记录，但它返回一个空列表。

索引的配置方式有问题吗？ 谢谢

这是示例数据：

{"camera_name": "Nikon", "photographer_name": "Aaron", "resolution": "1920x1080", "image_size": "3", "timestamp": 1397232415}
{"camera_name": "Nikon", "photographer_name": "Paul", "resolution": "1920x1080", "image_size": "4", "timestamp": 1717286853}
{"camera_name": "Nikon", "photographer_name": "Beth", "resolution": "720x480", "image_size": "1", "timestamp": 1503582086}
{"camera_name": "Nikon", "photographer_name": "Aaron", "resolution": "1920x1080", "image_size": "4", "timestamp": 1500628458}
{"camera_name": "Nikon", "photographer_name": "Paul", "resolution": "1920x1080", "image_size": "6", "timestamp": 1407580951}
{"camera_name": "Canon", "photographer_name": "Beth", "resolution": "1920x1080", "image_size": "5", "timestamp": 1166049453}
{"camera_name": "Canon", "photographer_name": "Paul", "resolution": "720x480", "image_size": "2", "timestamp": 1086317569}
{"camera_name": "Canon", "photographer_name": "Beth", "resolution": "720x480", "image_size": "1", "timestamp": 1400638926}
{"camera_name": "Canon", "photographer_name": "Aaron", "resolution": "720x480", "image_size": "1", "timestamp": 1345248762}
{"camera_name": "Canon", "photographer_name": "Paul", "resolution": "1920x1080", "image_size": "5", "timestamp": 1462360853}
{"camera_name": "Fuji", "photographer_name": "Beth", "resolution": "720x480", "image_size": "2", "timestamp": 1815298047}
{"camera_name": "Fuji", "photographer_name": "Shane", "resolution": "720x480", "image_size": "3", "timestamp": 1666493455}
{"camera_name": "Fuji", "photographer_name": "Beth", "resolution": "1920x1080", "image_size": "5", "timestamp": 1846677247}
{"camera_name": "Fuji", "photographer_name": "Beth", "resolution": "1920x1080", "image_size": "5", "timestamp": 1630996389}
{"camera_name": "Fuji", "photographer_name": "Shane", "resolution": "720x480", "image_size": "2", "timestamp": 1816829362}

我执行的查询：

1. camera_name=Nikon and timestamp<=1503582086 应该返回 4 条记录
2. camera_name='Fuji',photographer_name='Beth', resolution='1920x1080', image_size='5' and timestamp<=1900000000 应该返回 2 条记录，但我得到 0 条记录

Answer 1

索引不会“过滤”结果，它们允许您通过扫描索引树而不是扫描原始文档来更快地访问数据。

这意味着如果第二个查询“不返回任何内容”，它与您构建的任何索引都无关，但您使用的实际查询与数据库中的任何文档都不匹配。

我还将提到您的第二个索引可能会更小（取决于某些假设，如规模和数据分布），这可以帮助更新/插入性能，同时额外减少存储大小。 但是，从原始数据的外观来看，我认为这些并不是您的紧迫考虑。