Set Granularity for Time Series Data设置时间序列数据的粒度

Retrieve the Current Bucketing Parameters检索当前Bucketing参数

To retrieve current collection values, use the listCollections command:要检索当前集合值，请使用listCollections命令：

db.runCommand( { listCollections: 1 } )

For time series collections, the output contains granularity, bucketMaxSpanSeconds, and bucketRoundingSeconds parameters, if present.对于时间序列集合，输出包含granularity、bucketMaxSpanSeconds和bucketRoundingSeconds参数（如果存在）。

{
    cursor: {
       id: <number>,
       ns: 'test.$cmd.listCollections',
       firstBatch: [
         {
            name: <string>,
            type: 'timeseries',
            options: {
               expireAfterSeconds: <number>,
               timeseries: {
                  timeField: <string>,
                  metaField: <string>,
                  granularity: <string>,
                  bucketMaxSpanSeconds: <number>,
                  bucketRoundingSeconds: <number>
               }
            },
            ...
         },
         ...
       ]
    }
 }

Set the "granularity" Parameter设置“粒度”参数

The following example sets the granularity of a weather24h collection to minutes:以下示例将weather24h集合的granularity设置为minutes：

db.createCollection(
    "weather24h",
    {
       timeseries: {
          timeField: "timestamp",
          metaField: "metadata",
          granularity: "minutes"
       },
       expireAfterSeconds: 86400
    }
)

Using Custom Bucketing Parameters使用自定义桶参数

In MongoDB 6.3 and later, instead of granularity, you can set bucket boundaries manually using the two custom bucketing parameters. Consider this approach if you expect to query data for fixed time intervals, such as every 4 hours starting at midnight. 在MongoDB 6.3及更高版本中，您可以使用两个自定义桶参数手动设置桶边界，而不是granularity。如果您希望查询固定时间间隔的数据，例如从午夜开始的每4小时一次，请考虑这种方法。Ensuring buckets don't overlap between those periods optimizes for high query volume and insert operations.确保桶在这些时段之间不重叠，可以优化高查询量和insert操作。

To use custom bucketing parameters, set both parameters to the same value, and do not set granularity:要使用自定义bucketing参数，请将这两个参数设置为相同的值，并且不要设置granularity：

• bucketMaxSpanSeconds sets the maximum time between timestamps in the same bucket. Possible values are 1-31536000.设置同一桶中时间戳之间的最大时间间隔。可能的值为1-31536000。
• bucketRoundingSeconds sets the time interval that determines the starting timestamp for a new bucket. When a document requires a new bucket, MongoDB rounds down the document's timestamp value by this interval to set the minimum time for the bucket.设置确定新桶的开始时间戳的时间间隔。当文档需要一个新的桶时，MongoDB会按此间隔对文档的时间戳值进行四舍五入，以设置桶的最小时间。

For the weather station example, if you generate summary reports every 4 hours, you could adjust bucketing by setting the custom bucketing parameters to 14400 seconds instead of using a granularity of "minutes":以气象站为例，如果您每4小时生成一次摘要报告，则可以通过将自定义桶参数设置为14400秒而不是使用granularity:"minutes"来调整分组：

db.createCollection(
   "weather24h",
   {
      timeseries: {
         timeField: "timestamp",
         metaField: "metadata",
         bucketMaxSpanSeconds: 14400,
         bucketRoundingSeconds: 14400
      }
   }
)

If a document with a time of 2023-03-27T16:24:35Z does not fit an existing bucket, MongoDB creates a new bucket with a minimum time of 2023-03-27T16:00:00Z and a maximum time of 2023-03-27T19:59:59Z.如果时间为2023-03-27T16:24:35Z的文档不适合现有的桶，MongoDB将创建一个最小时间为2023:03-27T16:00:00Z、最大时间为2023-103-27T19:59:59Z的新桶。

Change Time Series Granularity更改时间序列粒度

You can increase timeseries.granularity from a shorter unit of time to a longer one using a collMod command.您可以使用collMod命令将timeseries.granularity从较短的时间单位增加到较长的时间单位。

db.runCommand( {
   collMod: "weather24h",
   timeseries: { granularity: "seconds" | "minutes" | "hours" }
} )

If you are using the custom bucketing parameters bucketRoundingSeconds and bucketMaxSpanSeconds instead of granularity, include both custom parameters in the collMod command and set them to the same value:如果使用自定义桶参数bucketRoundingSeconds和bucketMaxSpanSeconds而不是粒度，请在collMod命令中包含这两个自定义参数并将其设置为相同的值：

db.runCommand( {
   collMod: "weather24h",
   timeseries: {
      bucketRoundingSeconds: 86400,
      bucketMaxSpanSeconds: 86400
   }
} )

You cannot decrease the granularity interval or the custom bucketing values.您不能减小粒度间隔或自定义桶值。