SET BACKGROUND_DDL

You can use the SET BACKGROUND_DDL command to run DDL commands in the background.

​

Syntax

SET BACKGROUND_DDL = { true | false };

• By default, BACKGROUND_DDL is set as false to disable it, meaning that DDL operations will execute in the foreground. The DDL commands will be blocking and only return until the backfill process is completed.
• When BACKGROUND_DDL is set to true, any subsequent DDL operations will be executed in the background, allowing you to proceed with other tasks.

​

Supported DDL operations

​

Persistence

For materialized views being created in the background, their table definitions persist while they are being created, even if errors occur during checkpointing. This allows the materialized view jobs to be recovered from where they left off before the failure. Their table definitions and fragments will only be dropped if the job is canceled.

For materialized views being created in the foreground, their table and fragments will be cleaned up if checkpointing fails, if the cluster is restarted, or if the stream job is canceled.

The key difference is during the creating phase of a materialized view. After a materialized view is created (i.e. backfilling has completed), both foreground and background materialized views are functionally the same.

​

Background management

​

Monitor progress

You can monitor the progress of background DDL operations using the SHOW JOBS command. The exception is for sink jobs. These are immediately marked as completed, since their output will be immediately visible.

​

Cancel jobs

Currently background_ddl only supports sink and materialized views. You can just call DROP SINK or DROP MATERIALIZED VIEW on the corresponding relation to cancel it.

​

Set concurrent jobs

The maximum number of concurrent creating streaming jobs can be adjusted using the ALTER SYSTEM SET max_concurrent_creating_streaming_jobs command.

For example, you can set the maximum concurrent creating streaming jobs to 4:

ALTER SYSTEM SET max_concurrent_creating_streaming_jobs TO 4;

​

Examples

CREATE TABLE t (v1 int);

INSERT INTO t SELECT * FROM generate_series(1, 1000000);

SET BACKGROUND_DDL=true;

CREATE MATERIALIZED VIEW m AS SELECT * FROM t;
-- The "CREATE_MATERIALIZED_VIEW" response will be returned immediately.