Managing CDM Job Configuration

Maximum Concurrent Extractors

Maximum number of concurrent extraction tasks in a cluster

This parameter is also available on the Cluster Configuration page. You can change its value either on this page or the Cluster Configuration page.

By setting appropriate values for the Concurrent Extractors and Maximum Concurrent Extractors parameters, you can accelerate migration.

1. You are advised to set Maximum Concurrent Extractors to twice the number of vCPUs. For details, see Table 1.

   Table 1 Recommended maximum number of concurrent extractors for a CDM cluster

   Flavor	vCPUs/Memory	Recommended Maximum Concurrent Extractors
   cdm.large	8 vCPUs, 16 GB	16
   cdm.xlarge	16 vCPUs, 32 GB	32
   cdm.4xlarge	64 vCPUs, 128 GB	128

2. Configure the number of concurrent extractors based on the following rules:
   1. When data is to be migrated to files, CDM does not support multiple concurrent tasks. In this case, set a single process to extract data.
   2. If each row of the table contains less than or equal to 1 MB data, data can be extracted concurrently. If each row contains more than 1 MB data, it is recommended that data be extracted in a single thread.
   3. Set Concurrent Extractors for a job based on Maximum Concurrent Extractors for the cluster. It is recommended that the value of Concurrent Extractors is less than that of Maximum Concurrent Extractors.
   4. If the migration source is Hive and JDBC is used to read data, CDM does not support multi-concurrency. In this case, set the number of concurrent extractors to 1.
   5. If the destination is DLI, you are advised to set the number of concurrent extractors to 1. Otherwise, data may fail to be written.

Scheduled Backup/Restoration

This function depends on the OBS service. Backup files cannot be automatically aged. You need to manually delete backup files on a regular basis.

• Prerequisites

  An OBS link has been created. For details, see OBS Link Parameters.

• Scheduled backup

  On the Job Management page, click Settings and configure Scheduled Backup and its related parameters.

  Table 2 Scheduled backup parameters

  Parameter	Description	Example Value
  Scheduled Backup	Whether to enable automatic backup. This function is used to back up jobs but not links.	Enable
  Backup Policy	All jobs: CDM backs up all table/file migration jobs and entire DB migration jobs regardless of the job statuses. However, historical jobs are not backed up. All jobs by groups: You select one or more job groups to back up.	All jobs
  Backup Cycle	Select the backup cycle. Day: The backup is performed daily at 00:00:00. Week: The backup is performed at 00:00:00 every Monday. Month: The backup is performed at 00:00:00 on the first day of each month.	Day
  OBS Link for Writing Backups	Link used to back up jobs to OBS buckets. Select a link you have created on the Links page.	obslink
  OBS Bucket	OBS bucket where backup files are stored	cdm
  Backup Data Directory	Directory where backup files are stored	/cdm-bk/

• Restoring jobs

  If automatic backup has been performed, the backup list is displayed on the Configuration Management tab page. The OBS buckets where the backup files reside, backup paths, and backup time are displayed.

  You can click Restore Backup in the Operation column of the backup list to restore the CDM jobs.

Environment Variables of Job Parameters

When creating a migration job on CDM, the parameter (such as the OBS bucket name or file path) that can be manually configured, a field in a parameter, or a character in a field can be configured as a global variable, so that you can change parameter values in batches, or batch replace certain characters after jobs are exported or imported.

The following describes how to batch replace the OBS bucket name in a migration job.

1. On the Job Management page, click the Configuration Management tab and configure environment variables.

   bucket_1=A
   bucket_2=B

   Variable bucket_1 indicates bucket A, and variable bucket_2 indicates bucket B.

2. On the page for creating a CDM migration job, migrate data from bucket A to bucket B.

   Set the source bucket name to ${bucket_1} and destination bucket name to ${bucket_2}.

   Figure 1 Setting the bucket names to environment variables
   
3. If you want to migrate data from bucket C to bucket D, you do not need to change the job parameters. You only need to change the environment variables on the Configuration Management tab page as follows:

   bucket_1=C
   bucket_2=D