Help Center/ MapReduce Service/ Component Operation Guide (Normal)/ Using CarbonData (for MRS 3.x or Later)/ CarbonData Syntax Reference/ DML/ SET/RESET
Updated on 2022-09-15 GMT+08:00
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SET/RESET

Function

This command is used to dynamically add, update, display, or reset the CarbonData properties without restarting the driver.

Syntax

  • Add or Update parameter value:

    SET parameter_name=parameter_value

    This command is used to add or update the value of parameter_name.

  • Display property value:

    SET parameter_name

    This command is used to display the value of parameter_name.

  • Display session parameter:

    SET

    This command is used to display all supported session parameters.

  • Display session parameters along with usage details:

    SET -v

    This command is used to display all supported session parameters and their usage details.

  • Reset parameter value:

    RESET

    This command is used to clear all session parameters.

Parameter Description

Table 1 SET parameters

Parameter

Description

parameter_name

Name of the parameter whose value needs to be dynamically added, updated, or displayed

parameter_value

New value of parameter_name to be set

Precautions

The following table lists the properties which you can set or clear using the SET or RESET command.

Table 2 Properties

Property

Description

carbon.options.bad.records.logger.enable

Whether to enable bad record logger.

carbon.options.bad.records.action

Operations on bad records, for example, force, redirect, fail, or ignore. For more information, see •Bad record handling.

carbon.options.is.empty.data.bad.record

Whether the empty data is considered as a bad record. For more information, see Bad record handling.

carbon.options.sort.scope

Scope of the sort during data loading.

carbon.options.bad.record.path

HDFS path where bad records are stored.

carbon.custom.block.distribution

Whether to enable Spark or CarbonData block distribution.

enable.unsafe.sort

Whether to use unsafe sort during data loading. Unsafe sort reduces the garbage collection during data loading, thereby achieving better performance.

carbon.si.lookup.partialstring

If this is set to TRUE, the secondary index uses the starts-with, ends-with, contains, and LIKE partition condition strings.

If this is set to FALSE, the secondary index uses only the starts-with partition condition string.

carbon.input.segments

Segment ID to be queried. This property allows you to query a specified segment of a specified table. CarbonScan reads data only from the specified segment ID.

Syntax:

carbon.input.segments. <database_name>. <table_name> = < list of segment ids >

If you want to query a specified segment in multi-thread mode, you can use CarbonSession.threadSet instead of the SET statement.

Syntax:

CarbonSession.threadSet ("carbon.input.segments. <database_name>. <table_name>","< list of segment ids >");

NOTE:

You are advised not to set this property in the carbon.properties file because all sessions contain the segment list unless session-level or thread-level overwriting occurs.

Examples

  • Add or Update:

    SET enable.unsafe.sort=true

  • Display property value:

    SET enable.unsafe.sort

  • Show the segment ID list, segment status, and other required details, and specify the segment list to be read:

    SHOW SEGMENTS FOR TABLE carbontable1;

    SET carbon.input.segments.db.carbontable1 = 1, 3, 9;

  • Query a specified segment in multi-thread mode:

    CarbonSession.threadSet ("carbon.input.segments.default.carbon_table_MulTI_THread", "1,3");

  • Use CarbonSession.threadSet to query segments in a multi-thread environment (Scala code is used as an example): 
    def main(args: Array[String]) {
 Future {              CarbonSession.threadSet("carbon.input.segments.default.carbon_table_MulTI_THread", "1")
      spark.sql("select count(empno) from carbon_table_MulTI_THread").show()
    }
}
  • Reset:

    RESET

System Response

  • Success will be recorded in the driver log.
  • Failure will be displayed on the UI.
Parent topic: DML