SET STATEMENT

The SET statement is used to set system variables of OpenMLDB. At present, the system variables of OpenMLDB include session system variables and global system variables. Modifications to session variables will only affect the current session (that is, the current database connection). Modifications to global variables take effect for all sessions.

Syntax

SetStatement ::=
    'SET' variableName '=' value

variableName ::=
	sessionVariableName
	
sessionVariableName ::= '@@'Identifier | '@@session.'Identifier | '@@global.'Identifier

The following format is also equivalent.

'SET' [ GLOBAL | SESSION ] <variableName> '=' <value>

• Session system variables are usually prefixed with @session, such as SET @@session.execute_mode = “offline”. Session system variables can also be optionally prefixed with @@ directly, that is, SET @@execute_mode = "offline" is equivalent to the previous configuration statement.

• Global system variables are prefixed with @global, such as SET @@global.enable_trace = true;

• SET STATEMENT can only be used to set/modify existing (built-in) system variables.

• Variable names are case-insensitive.

Currently Supported System Variables

SESSION System Variable

SESSION System Variable	Note	Variable Value	Default Value
@@session.execute_mode｜@@execute_mode	The execution mode of OpenMDLB in the current session. Currently supports offline and online two modes. In offline execution mode, only offline data will be imported/inserted and queried. In online execution mode, only online data will be imported/inserted and queried.	offline, online"	online
@@session.enable_trace｜@@enable_trace	When the value is true, an error message stack will be printed when the SQL statement has a syntax error or an error occurs during the plan generation process. When the value is false, only the basic error message will be printed if there is a SQL syntax error or an error occurs during the plan generation process.	true, false	false
@@session.sync_job｜@@sync_job	When the value is true, the offline command will be executed synchronously, waiting for the final result of the execution. When the value is false, the offline command returns immediately. If you need to check the execution, please use SHOW JOB command.	true, false	false
@@session.sync_timeout｜@@sync_timeout	When sync_job=true, you can configure the waiting time for synchronization commands. The timeout will return immediately. After the timeout returns, you can still view the command execution through SHOW JOB.	Int	20000
@@session.spark_config｜@@spark_config	Set the Spark configuration for offline jobs, configure like ‘spark.executor.memory=2g;spark.executor.cores=2’. Notice that the priority of this Spark configuration is higer than TaskManager Spark configuration but lower than CLI Spark configuration file.	String	“”
@@session.insert_memory_usage_limit ｜@@insert_memory_usage_limit	Set server memory usage limit when inserting or importing data. If the server memory usage exceeds the set value, the insertion will fail. The value range is 0-100. 0 means unlimited	Int	“0”

Example

Set and Display Session System Variables

> SHOW VARIABLES;
 --------------- ---------
  Variable_name   Value
 --------------- ---------
  enable_trace    false
  execute_mode    offline
  job_timeout     20000
  sync_job        false
 --------------- ---------

4 rows in set
> SET @@session.execute_mode = "online";
-- SUCCEED
> SHOW VARIABLES;
 --------------- ---------
  Variable_name   Value
 --------------- ---------
  enable_trace    false
  execute_mode    online
  job_timeout     20000
  sync_job        false
 --------------- ---------

4 rows in set
> SET @@session.enable_trace = "true";
 -- SUCCEED
> SHOW VARIABLES;
  --------------- ---------
  Variable_name   Value
 --------------- ---------
  enable_trace    true
  execute_mode    online
  job_timeout     20000
  sync_job        false
 --------------- ---------

4 rows in set

Set and Display Global System Variables

> SHOW GLOBAL VARIABLES;
 --------------- ----------------
  Variable_name   Variable_value
 --------------- ----------------
  enable_trace    false
  sync_job        false
  job_timeout     20000
  execute_mode    offline
 --------------- ----------------

4 rows in set
> SET @@global.enable_trace = "true";
-- SUCCEED
> SHOW GLOBAL VARIABLES;
 --------------- ----------------
  Variable_name   Variable_value
 --------------- ----------------
  enable_trace    true
  sync_job        false
  job_timeout     20000
  execute_mode    offline
 --------------- ----------------

4 rows in set

Configure enable_trace

• Create a database db1 and create table t1.

CREATE DATABASE db1;
-- SUCCEED
USE db1;
-- SUCCEED: Database changed
CREATE TABLE t1 (col0 STRING, col1 int, std_time TIMESTAMP, INDEX(KEY=col1, TS=std_time, TTL_TYPE=absolute, TTL=30d));
--SUCCEED

• When enable_trace is false, executing an invalid SQL will generate the following information.

> set @@enable_trace = "false";
-- SUCCEED    
> select sum(col1) over w1 from t1 window w1 as (partition by col1 order by col0 rows_range between 10d preceding and current row);
-- ERROR: Invalid Order column type : kVarchar

• When enable_trace is true, executing an invalid SQL will generate the following information.

> set @@enable_trace = "true";
-- SUCCEED
> select sum(col1) over w1 from t1 window w1 as (partition by col1 order by col0 rows_range between 10d preceding and current row);
-- ERROR: Invalid Order column type : kVarchar
    (At /Users/chenjing/work/chenjing/OpenMLDB/hybridse/src/vm/sql_compiler.cc:263)
    (At /Users/chenjing/work/chenjing/OpenMLDB/hybridse/src/vm/sql_compiler.cc:166)
    (Caused by) Fail to generate physical plan batch mode
    (At /Users/chenjing/work/chenjing/OpenMLDB/hybridse/src/vm/transform.cc:1672)
    (Caused by) Fail to transform query statement
    (At /Users/chenjing/work/chenjing/OpenMLDB/hybridse/src/vm/transform.cc:103)
    (At /Users/chenjing/work/chenjing/OpenMLDB/hybridse/src/vm/transform.cc:1249)
    (At /Users/chenjing/work/chenjing/OpenMLDB/hybridse/src/vm/transform.cc:1997)

Offline Commands Configuration Details

• Set the synchronous execution for offline commands:

> SET @@sync_job = "true";

Caution

If offline sync job is longer than 30min(the default timeout for offline sync job), you should change the config of TaskManager and client.

• set server.channel_keep_alive_time bigger in TaskManager config file.

• choose one:

  • set a bigger session job_timeout, we’ll use max(session_job_timeout, default_gflag_sync_job_timeout).

  • set --sync_job_timeout of sql client, less than server.channel_keep_alive_time. SDK can’t change the config now.

• Set the waiting time for offline async commands or offline admin commands (in milliseconds):

> SET @@job_timeout = "600000";

Related SQL Statements

SHOW VARIABLES