Read data from a Lastpoint index

Use Tablestore SDK for Java to read the latest data point of each time series from a Lastpoint index by primary key range.

Prerequisites

Install the Tablestore SDK for Java and initialize a client. Lastpoint indexes require version 5.17.1 or later. We recommend that you use the latest version.

Description

A Lastpoint index can be read as a data table. Call getRange and specify a primary key range to read the latest data points in the range. For a time series table that uses the default time series identifiers, the Lastpoint index contains the _#h, _m_name, _data_source, and _tags primary key columns in this order.

public GetRangeResponse getRange(GetRangeRequest getRangeRequest) throws TableStoreException, ClientException

The following example sets the start values of the four primary key columns to INF_MIN and the end values to INF_MAX. The example then reads all data from example_lastpoint_index across multiple pages.

RangeRowQueryCriteria criteria =
        new RangeRowQueryCriteria("example_lastpoint_index");

PrimaryKey startPrimaryKey = PrimaryKeyBuilder.createPrimaryKeyBuilder()
        .addPrimaryKeyColumn("_#h", PrimaryKeyValue.INF_MIN)
        .addPrimaryKeyColumn("_m_name", PrimaryKeyValue.INF_MIN)
        .addPrimaryKeyColumn("_data_source", PrimaryKeyValue.INF_MIN)
        .addPrimaryKeyColumn("_tags", PrimaryKeyValue.INF_MIN)
        .build();
PrimaryKey endPrimaryKey = PrimaryKeyBuilder.createPrimaryKeyBuilder()
        .addPrimaryKeyColumn("_#h", PrimaryKeyValue.INF_MAX)
        .addPrimaryKeyColumn("_m_name", PrimaryKeyValue.INF_MAX)
        .addPrimaryKeyColumn("_data_source", PrimaryKeyValue.INF_MAX)
        .addPrimaryKeyColumn("_tags", PrimaryKeyValue.INF_MAX)
        .build();

criteria.setInclusiveStartPrimaryKey(startPrimaryKey);
criteria.setExclusiveEndPrimaryKey(endPrimaryKey);
criteria.setMaxVersions(1);

while (true) {
    GetRangeResponse response =
            client.getRange(new GetRangeRequest(criteria));
    response.getRows().forEach(System.out::println);

    if (response.getNextStartPrimaryKey() == null) {
        break;
    }
    criteria.setInclusiveStartPrimaryKey(
            response.getNextStartPrimaryKey());
}

Parameters

GetRangeRequest contains the following parameter.

Name	Type	Description
rangeRowQueryCriteria (required)	`RangeRowQueryCriteria`	The range read criteria.

Range read criteria

rangeRowQueryCriteria contains the following parameters.

Name	Type	Description
tableName (required)	`String`	The Lastpoint index name.
inclusiveStartPrimaryKey (required)	`PrimaryKey`	The inclusive start primary key. Specify all primary key columns in the order defined in the index.
exclusiveEndPrimaryKey (required)	`PrimaryKey`	The exclusive end primary key. Specify all primary key columns in the order defined in the index.
maxVersions (required)	`int`	The maximum number of versions to return for each column. A Lastpoint index retains only the latest value of each field. Set this parameter to `1`.
columnsToGet (optional)	`Set<String>`	The attribute columns to return. If this parameter is not specified, all attribute columns are returned.
direction (optional)	`Direction`	The read direction. Valid values: `FORWARD` and `BACKWARD`. Default value: `FORWARD`.
limit (optional)	`int`	The maximum number of rows to return in a request. The value must be greater than `0`. If this parameter is not specified, the SDK default of `-1` is used.

Response

GetRangeResponse contains the following operation-specific fields.

Field	Type	Description
`rows`	`List<Row>`	Call `getRows()` to obtain the Lastpoint rows returned by the request.
`nextStartPrimaryKey`	`PrimaryKey`	Call `getNextStartPrimaryKey()` to obtain the start primary key for the next request. A value of `null` indicates that all data in the specified range is returned.

Lastpoint row schema

For a time series table that uses the default time series identifiers, each Lastpoint row contains the following fields.

Field	Type	Description
`_#h`	`String`	The system-generated partition key for the time series.
`_m_name`	`String`	The measurement name.
`_data_source`	`String`	The data source.
`_tags`	`String`	The time series tags.
`_time`	`long`	The timestamp of the latest data point, in microseconds.
Data fields	`ColumnValue`	The data fields and values in the latest data point.