将全表的数据在逻辑上划分成接近指定大小的若干分片,返回这些分片之间的分割点以及分片所在机器的提示。一般用于计算引擎规划并发度等执行计划。
请求结构
message ComputeSplitPointsBySizeRequest {
required string table_name = 1;
required int64 split_size = 2; // in 100MB
}
- 类型:string。
- 是否必要参数:是
- 要切分的数据所在的表名。
- 类型:int64
- 是否必要参数:是
- 每个分片的近似大小,以百兆为单位。
响应消息结构
message ComputeSplitPointsBySizeResponse {
required ConsumedCapacity consumed = 1;
repeated PrimaryKeySchema schema = 2;
/**
* Split points between splits, in the increasing order
*
* A split is a consecutive range of primary keys,
* whose data size is about split_size specified in the request.
* The size could be hard to be precise.
*
* A split point is an array of primary-key column w.r.t. table schema,
* which is never longer than that of table schema.
* Tailing -inf will be omitted to reduce transmission payloads.
*/
repeated bytes split_points = 3;
/**
* Locations where splits lies in.
*
* By the managed nature of TableStore, these locations are no more than hints.
* If a location is not suitable to be seen, an empty string will be placed.
*/
message SplitLocation {
required string location = 1;
required sint64 repeat = 2;
}
repeated SplitLocation locations = 4;
}
- 类型:ConsumedCapacity
- 本次请求消耗的服务能力单元。
- 类型:PrimaryKeySchema
- 该表的 Schema,与建表时给出的 Schema 相同。
- 类型:repeated bytes
- 分片之间的分割点。分割点之间保证单调增。每个分割点都是以Plainbuffer编码的行,并且只有primary-key项。为了减少传输的数据量,分割点最后的-inf不会传输。
- 类型:repeated SplitLocation
- 分割点所在机器的提示。可以为空。
举个例子,如果有一张表有三列主键,其中首列主键类型为string。调用这个API后得到5个分片,分别为(-inf,-inf,-inf)
到("a",-inf,-inf)
、("a",-inf,-inf)
到("b",-inf,-inf)
、("b",-inf,-inf)
到("c",-inf,-inf)
、("c",-inf,-inf)
到("d",-inf,-inf)
和("d",-inf,-inf)
到(+inf,+inf,+inf)
。前三个落在"machine-A",后两个落在"machine-B"。那么,split_points为(示意)[("a"),("b"),("c"),("d")]
,而locations为(示意)"machine-A"*3, "machine-B"*2
。
服务能力单元消耗
消耗的读服务能力单元数量与分片的数量相同。不消耗写服务能力单元。