View and configure runtime parameters

What are runtime parameters?

Runtime parameters are variables that can be set at runtime to configure the behavior of RisingWave. They are also known as session variables.

How to view runtime parameters?

You can use the SHOW ALL command to view the runtime parameters, their current settings, and some notes about these parameters.

SHOW ALL;

For example, you may see a table similar to this:

Runtime Parameters

          Name                  |     Setting     |        Description
--------------------------------+-----------------+--------------------------------------
 implicit_flush                 | false           | If set to `true`, every INSERT/UPDATE/DELETE statement will block until the entire dataflow is refreshed.
 create_compaction_group_for_mv | false           | If set to `true`, RisingWave will create dedicated compaction groups when creating these materialized views.
 query_mode                     | auto            | A temporary config variable to force query running in either local or distributed mode. If the value is auto, the system will decide for you automatically.
 ...

Below is the detailed information about the parameters you may see after using the SHOW ALL command:

Name	Values or examples	Description
implicit_flush	true/false	If set to true, every INSERT/UPDATE/DELETE statement will block until the entire dataflow is refreshed. In other words, every related table & MV will be able to see the write.
create_compaction_group_for_mv	true/false	If set to true, RisingWave will create dedicated compaction groups when creating these materialized views.
query_mode	auto	A temporary config variable to force query running in either local or distributed mode. The default value is auto which means let the system decide to run batch queries in local or distributed mode automatically.
extra_float_digits	1	Set the number of digits displayed for floating-point values. See here for details.
application_name	psql	Set the application name to be reported in statistics and logs. See here for details.
datestyle	DMY	It is typically set by an application upon connection to the server. See here for details.
batch_enable_lookup_join	true/false	Force the use of lookup join instead of hash join when possible for local batch execution.
batch_enable_sort_agg	true/false	Enable usage of sortAgg instead of hash agg when order property is satisfied in batch execution.
batch_enable_distributed_dml	true/false	Enable distributed DML, allowing INSERT/UPDATE/DELETE statements to be executed in a distributed way, such as running on multiple compute nodes. Defaults to false.
batch_expr_strict_mode	true/false	Control whether to let the entire query fail or fill NULL values for expression evaluation failures.
max_split_range_gap	8	The max gap allowed to transform small range scan into multi point lookup.
search_path	”$user”, public	Set the order in which schemas are searched when an object (table, data type, function, etc.) is referenced by a simple name with no schema specified. See here for details.
visibility_mode	default	If VISIBILITY_MODE is all, we will support querying the latest uncommitted data, and consistency is not guaranteed between the tables.
transaction_isolation	read committed	See here for details.
query_epoch	0	Select as of specific epoch. Sets the historical epoch for querying data. If 0, querying latest data.
timezone	UTC	Session timezone. Defaults to UTC.
streaming_parallelism	ADAPTIVE/0,1,2,…	If STREAMING_PARALLELISM is non-zero, CREATE MATERIALIZED VIEW/TABLE/INDEX will use it as streaming parallelism.
streaming_enable_delta_join	true/false	Enable delta join for streaming queries. Defaults to false.
streaming_enable_bushy_join	true/false	Enable bushy join for streaming queries. Defaults to true.
streaming_use_arrangement_backfill	true/false	Enable arrangement backfill for streaming queries. Defaults to true.
streaming_use_snapshot_backfill	true/false	Enable snapshot backfill for streaming queries. Defaults to false.
enable_join_ordering	true/false	Enable join ordering for streaming and batch queries. Defaults to true.
enable_two_phase_agg	true/false	Enable two phase agg optimization. Defaults to true. Setting this to true will always set FORCE_TWO_PHASE_AGG to false.
force_two_phase_agg	true/false	Force two phase agg optimization whenever there’s a choice between optimizations. Defaults to false. Setting this to true will always set ENABLE_TWO_PHASE_AGG to false.
enable_share_plan	true/false	Enable sharing of common sub-plans. This means that DAG structured query plans can be constructed, rather than only tree structured query plans.
force_split_distinct_agg	true/false	Enable split distinct agg.
intervalstyle	postgres	Set the display format for interval values. It is typically set by an application upon connection to the server. See here for details.
batch_parallelism	0	If BATCH_PARALLELISM is non-zero, batch queries will use this parallelism.
server_version	9.5.0	The version of PostgreSQL that Risingwave claims to be.
server_version_num	90500	The version of PostgreSQL that Risingwave claims to be.
client_min_messages	notice	See here for details.
client_encoding	UTF8	See here for details.
sink_decouple	default	Enable decoupling sink and internal streaming graph or not.
synchronize_seqscans	true/false	See here for details. Unused in RisingWave, support for compatibility.
statement_timeout	3600	Abort query statement that takes more than the specified amount of time in sec. If log_min_error_statement is set to ERROR or lower, the statement that timed out will also be logged. The default value is 1 hour.
lock_timeout	0	See here for details. Unused in RisingWave, support for compatibility.
cdc_source_wait_streaming_start_timeout	30	For limiting the startup time of a shareable CDC streaming source when the source is being created. Unit: seconds.
row_security	true/false	See here for details. Unused in RisingWave, support for compatibility.
standard_conforming_strings	on	See here for details.
source_rate_limit	default/positive integer/0	Set the maximum number of records per second per source, for each parallelism. This parameter is applied when creating new sources and tables with sources. The value can be default, 0, or a positive integer. Set it to 0 will pause the source read for sources. Set it to default will remove the rate limit. Setting this variable will only affect new DDLs within the session, but not change the rate limits of existing jobs. Use ALTER to change the rate limits in existing sources and tables that have source. Note that the total throughput of a streaming job is determined by multiplying the parallelism with the throttle rate. To obtain the parallelism value for a streaming job, you can refer to the streaming_parallelism runtime parameter in this table.
backfill_rate_limit	default/positive integer/0	Set the maximum number of records per second per parallelism for the backfill process of materialized views, sinks, and indexes. This parameter is applied when creating new jobs, and throttles the backfill from upstream materialized views and sources. The value can be default, 0, or a positive integer. Set it to 0 will pause the backfill. Set it to default will remove the backfill rate limit. Setting this variable will only affect new DDLs within the session, but not change the rate limits of existing jobs. Use ALTER to change the backfill rate limits in existing materialized views and CDC tables. Note that the total throughput of a streaming job is determined by multiplying the parallelism with the throttle rate. To obtain the parallelism value for a streaming job, you can refer to the streaming_parallelism runtime parameter in this table.
dml_rate_limit	positive integer/0	Set streaming rate limit (rows per second) for each parallelism for table DML. Set it to -1 will disable rate limit. Set it to 0 will pause the DML.
sink_rate_limit	positive integer/0	Set sink rate limit (rows per second) for each parallelism for external sink. Set it to -1 will disable rate limit. Set it to 0 will pause the sink.
streaming_over_window_cache_policy	full	Cache policy for partition cache in streaming over window. Can be full, recent, recent_first_n or recent_last_n.
background_ddl	true/false	Run DDL statements in background.
server_encoding	UTF8	Show the server-side character set encoding. At present, this parameter can be shown but not set, because the encoding is determined at database creation time.
bytea_output	hex	Set the output format for values of type bytea. Valid values are hex (the default) and escape (the traditional PostgreSQL format). The bytea type always accepts both formats on input, regardless of this setting.
iceberg_engine_connection	string	Specifies the connection information for the Iceberg engine tables. Create an Iceberg connection and set this variable before creating Iceberg engine tables. The format should be schema_name.connection_name.

If you just want to view a specific parameter’s value, you can also use the SHOW command.

SHOW parameter_name;

How to configure runtime parameters?

You can use SET command or the set_config() function to change the setting of a runtime parameter.

The syntax of the SET command is:

SET parameter_name { TO | = } { value | 'value' | DEFAULT};

Where parameter_name is the name of the parameter, and value or 'value' is the new value of the parameter. DEFAULT can be written to specify resetting the parameter to its default value.

For details about the set_config() function, see System administration functions, and for details about the SET command, see SET.

SET applies only to the current session.

You can also use the ALTER SYSTEM SET command to set a system-wide default value for a runtime parameter. This configuration will then be applied to every new session.

ALTER SYSTEM SET takes effect in new sessions. The value of the runtime parameter remains unchanged in the current session.

Syntax

ALTER SYSTEM SET session_param_name TO session_param_value;