Optimizer Method Configuration

enable_bitmapscan

Parameter description: Controls whether the query optimizer uses the bitmap-scan plan type.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_hashagg

Parameter description: Controls whether the query optimizer uses the Hash aggregation plan type.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_mixedagg

Parameter description: Controls whether the query optimizer uses the Mixed Agg plan type. (This parameter is supported by version 8.2.0 or later clusters.)

Type: USERSET

Value range: Boolean

• on indicates that a Mixed Agg query plan is generated for the Grouping Sets statement (including Rollup or Cube) that meets certain conditions.
• off indicates it is disabled.

Default value: off

The Mixed Agg query plan can be used to improve the performance of statements dealing with a large amount of data (the data volume of a single DN table is greater than 100 GB).

Mixed Agg is not supported in the following scenarios:

• The data type of the columns in the GROUP BY clause do not support hashing.
• The aggregate function uses DISTINCT for deduplication or ORDER BY for sorting.
• The GROUPING SETS clause does not contain empty groups.

enable_hashjoin

Parameter description: Controls whether the query optimizer uses the Hash-join plan type.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_indexscan

Parameter description: Controls whether the query optimizer uses the index-scan plan type.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_indexonlyscan

Parameter description: Controls whether the query optimizer uses the index-only-scan plan type.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_material

Parameter description: Controls whether the query optimizer uses materialization. It is impossible to suppress materialization entirely, but setting this parameter to off prevents the optimizer from inserting materialized nodes.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_mergejoin

Parameter description: Controls whether the query optimizer uses the merge-join plan type.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: off

enable_nestloop

Parameter description: Controls whether the query optimizer uses the nested-loop join plan type to fully scan internal tables. It is impossible to suppress nested-loop joins entirely, but setting this parameter to off allows the optimizer to choose other methods if available.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: off

enable_index_nestloop

Parameter description: Controls whether the query optimizer uses the nested-loop join plan type to scan the parameterized indexes of internal tables.

Type: USERSET

Value range: Boolean

• on indicates the query optimizer uses the nested-loop join plan type.
• off indicates the query optimizer does not use the nested-loop join plan type.

Default value: The default value for a newly installed cluster is on. If the cluster is upgraded from R8C10, the forward compatibility is retained. If the version is upgraded from R7C10 or an earlier version, the default value is off.

enable_seqscan

Parameter description: Controls whether the query optimizer uses the sequential scan plan type. It is impossible to suppress sequential scans entirely, but setting this variable to off allows the optimizer to preferentially choose other methods if available.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_sort

Parameter description: Controls whether the query optimizer uses the sort method. It is impossible to suppress explicit sorts entirely, but setting this variable to off allows the optimizer to preferentially choose other methods if available.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_tidscan

Parameter description: Controls whether the query optimizer uses the Tuple ID (TID) scan plan type.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_kill_query

Parameter description: In CASCADE mode, when a user is deleted, all the objects belonging to the user are deleted. This parameter specifies whether the queries of the objects belonging to the user can be unlocked when the user is deleted.

Type: SUSET

Value range: Boolean

• on indicates the unlocking is allowed.
• off indicates the unlocking is not allowed.

Default value: off

enforce_oracle_behavior

Parameter description: Controls the rule matching modes of regular expressions.

Type: USERSET

Value range: Boolean

• on indicates that the ORACLE matching rule is used.
• off indicates that the POSIX matching rule is used.

Default value: on

enable_stream_concurrent_update

Parameter description: Controls the use of stream in concurrent updates. This parameter is restricted by the enable_stream_operator parameter.

Type: USERSET

Value range: Boolean

• on indicates that the optimizer can generate stream plans for the UPDATE statement.
• off indicates that the optimizer can generate only non-stream plans for the UPDATE statement.

Default value: on

enable_stream_ctescan

Parameter description: Specifies whether a stream plan supports ctescan.

Type: USERSET

Value range: Boolean

• on indicates that ctescan is supported for the stream plan.
• off indicates that ctescan is not supported for the stream plan.

Default value: off

enable_stream_operator

Parameter description: Controls whether the query optimizer uses streams.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_stream_recursive

Parameter description: Specifies whether to push WITH RECURSIVE join queries to DNs for processing.

Type: USERSET

Value range: Boolean

• on: WITH RECURSIVE join queries will be pushed down to DNs.
• off: WITH RECURSIVE join queries will not be pushed down to DNs.

Default value: on

enable_value_redistribute

Parameter description: Specifies whether to generate value redistribute plans. In 8.2.0 and later cluster versions, this parameter takes effect for rank, dense_rank, and row_number without the PARTITION BY clause.

Type: USERSET

Value range: Boolean

• on indicates that value redistribute plans are generated.
• off indicates that no value redistribute plans are generated.

Default value: on

max_recursive_times

Parameter description: Specifies the maximum number of WITH RECURSIVE iterations.

Type: USERSET

Value range: an integer ranging from 0 to INT_MAX

Default value: 200

enable_vector_engine

Parameter description: Controls whether the query optimizer uses the vectorized executor.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_broadcast

Parameter description: Controls whether the query optimizer uses the broadcast distribution method when it evaluates the cost of stream.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: on

enable_change_hjcost

Parameter description: Specifies whether the optimizer excludes internal table running costs when selecting the Hash Join cost path. If it is set to on, tables with a few records and high running costs are more possible to be selected.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: off

enable_fstream

Parameter description: Controls whether the query optimizer uses streams when it delivers statements. This parameter is only used for external HDFS tables.

This parameter has been discarded. To reserve forward compatibility, set this parameter to on, but the setting does not make a difference.

Type: USERSET

Value range: Boolean

• on indicates it is enabled.
• off indicates it is disabled.

Default value: off

enable_hashfilter

Parameter description: Controls whether hashfilters can be generated for plans that contain replication tables (including dual and constant tables). This parameter is supported by version 8.2.0 or later clusters.

Type: USERSET

Value range: Boolean

• on indicates that hashfilters can be generated.
• off indicates that no hashfilters can be generated.

Default value: on

best_agg_plan

This parameter is used to control the query optimizer to generate which type of hashagg plans.

Type: USERSET

Value range: an integer ranging from 0 to 3.

• When the value is set to 1, the first plan is forcibly generated.
• When the value is set to 2 and if the group by column can be redistributed, the second plan is forcibly generated. Otherwise, the first plan is generated.
• When the value is set to 3 and if the group by column can be redistributed, the third plan is generated. Otherwise, the first plan is generated.
• When the value is set to 0, the query optimizer chooses the most optimal plan based on the estimated costs of the three plans above.

Default value: 0

volatile_shipping_version

Parameter description: Controls the execution scope of volatile functions to be pushed down. This parameter is supported by version 8.2.0 or later clusters.

Type: USERSET

Value range: 0, 1

• If this parameter is set to 1, the nextval, uuid_generate_v1, sys_guid, and uuid functions can be completely pushed down if they are in the target column of a statement.
• If this parameter is set to 0, random functions can be completely pushed down. The nextval and uuid_generate_v1 functions can be pushed down only if INSERT contains simple query statements.

Default value: 1

agg_redistribute_enhancement

Parameter description: When the aggregate operation is performed, which contains multiple group by columns and all of the columns are not in the distribution column, you need to select one group by column for redistribution. This parameter controls the policy of selecting a redistribution column.

Type: USERSET

Value range: Boolean

• on indicates the column that can be redistributed and evaluates the most distinct value for redistribution.
• off indicates the first column that can be redistributed for redistribution.

Default value: off

enable_valuepartition_pruning

Parameter description: Specifies whether the DFS partitioned table is dynamically or statically optimized.

Type: USERSET

Value range: Boolean

• on indicates that the DFS partitioned table is dynamically or statically optimized.
• off indicates that the DFS partitioned table is not dynamically or statically optimized.

Default value: on

expected_computing_nodegroup

Parameter description: Specifies a computing Node Group or the way to choose such a group. The Node Group mechanism is now for internal use only. You do not need to set it.

During join or aggregation operations, a Node Group can be selected in four modes. In each mode, the specified candidate computing Node Groups are listed for the optimizer to select an appropriate one for the current operator.

Type: USERSET

Value range: a string

• optimal: The list of candidate computing Node Groups consists of the Node Group where the operator's operation objects are located and the DNs in the Node Groups on which the current user has the COMPUTE permission.
• query: The list of candidate computing Node Groups consists of the Node Group where the operator's operation objects are located and the DNs in the Node Groups where base tables involved in the query are located.
• bind: If the current session user is a logical cluster user, the candidate computing Node Group is the Node Group of the logical cluster associated with the current user. If the session user is not a logical cluster user, the candidate computing Node Group selection rule is the same as that when this parameter is set to query.
• Node Group name:
  • If enable_nodegroup_debug is set to off, the list of candidate computing Node Groups consists of the Node Group where the operator's operation objects are located and the specified Node Group.
  • If enable_nodegroup_debug is set to on, the specified Node Group is used as the candidate Node Group.

Default value: bind

enable_nodegroup_debug

Parameter description: Specifies whether the optimizer assigns computing workloads to a specific Node Group when multiple Node Groups exist in an environment. The Node Group mechanism is now for internal use only. You do not need to set it.

This parameter takes effect only when expected_computing_nodegroup is set to a specific Node Group.

Type: USERSET

Value range: Boolean

• on indicates that computing workloads are assigned to the Node Group specified by expected_computing_nodegroup.
• off indicates no Node Group is specified to compute.

Default value: off

stream_multiple

Parameter description: Specifies the weight used for optimizer to calculate the final cost of stream operators.

The base stream cost is multiplied by this weight to make the final cost.

Type: USERSET

Value range: a floating point number ranging from 0 to DBL_MAX

Default value: 1

This parameter is applicable only to Redistribute and Broadcast streams.

qrw_inlist2join_optmode

Parameter description: Specifies whether enable inlist-to-join (inlist2join) query rewriting.

Type: USERSET

Value range: a string

• disable: inlist2join disabled
• cost_base: cost-based inlist2join query rewriting
• rule_base: forcible rule-based inlist2join query rewriting
• A positive integer: threshold of Inlist2join query rewriting. If the number of elements in the list is greater than the threshold, the rewriting is performed.

Default value: cost_base

setop_optmode

Parameter description: Specifies whether to perform deduplication on the query branch statements of a set operation (UNION/EXCEPT/INTERSECT) without the ALL option. This parameter is supported by version 8.2.0 or later clusters.

Type: USERSET

Value range: enumerated values

• disable: The query branch does not perform deduplication.
• force: The query branch forcibly performs deduplication.
• cost: The optimizer compares the costs of query branches with and without deduplication, and choose the execution mode with lower costs.

The default value is disable.

This parameter takes effect only if the execution plan of a SQL statement meets the following conditions:

• The UNION, EXCEPT, and INTERSECT operations in the SQL statement do not contain the ALL option.
• Data redistribution has been performed on the query branches where the set operation is to be performed.

skew_option

Parameter description: Specifies whether an optimization policy is used

Type: USERSET

Value range: a string

• off: policy disabled
• normal: radical policy. All possible skews are optimized.
• lazy: conservative policy. Uncertain skews are ignored.

Default value: normal