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Optimizer Method Configuration

These configuration parameters provide a crude method of influencing the query plans chosen by the query optimizer. If the default plan chosen by the optimizer for a particular query is not optimal, a temporary solution is to use one of these configuration parameters to force the optimizer to choose a different plan. Better ways include adjusting the optimizer cost constants, manually running ANALYZE, increasing the value of the default_statistics_target configuration parameter, and adding the statistics collected in a specific column using ALTER TABLE SET STATISTICS.

enable_bitmapscan

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

Type: USERSET

Value range: Boolean

  • on indicates the query optimizer uses the bitmap-scan plan type.
  • off indicates the query optimizer does not use the bitmap-scan plan type.

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 the query optimizer uses the Hash aggregation plan type.
  • off indicates the query optimizer does not use the Hash aggregation plan type.

Default value: on

enable_hashjoin

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

Type: USERSET

Value range: Boolean

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

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 the query optimizer uses the index-scan plan type.
  • off indicates the query optimizer does not use the index-scan plan type.

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 the query optimizer uses the index-only-scan plan type.
  • off indicates the query optimizer does not use the index-only-scan plan type.

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 the query optimizer uses materialization.
  • off indicates the query optimizer does not use materialization.

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 the query optimizer uses the merge-join plan type.
  • off indicates the query optimizer does not use the merge-join plan type.

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 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: 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: on

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 the query optimizer uses the sequential scan plan type.
  • off indicates the query optimizer does not use the sequential scan plan type.

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 the query optimizer uses the sort method.
  • off indicates the query optimizer does not use the sort method.

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 the query optimizer uses the TID scan plan type.
  • off indicates the query optimizer does not use the TID scan plan type.

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_operator

Parameter description: Controls whether the query optimizer uses streams.

Type: USERSET

Value range: Boolean

  • on indicates the query optimizer uses streams.
  • off indicates the query optimizer does not use streams.

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

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 the query optimizer uses the vectorized executor.
  • off indicates the query optimizer does not use the vectorized executor.

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 the query optimizer uses the broadcast distribution method.
  • off indicates the query optimizer does not use the broadcast distribution method.

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: SUSET

Value range: Boolean

  • on indicates the optimizer excludes internal table running costs when selecting the Hash Join cost path.
  • off indicates the optimizer does not exclude internal table running costs when selecting the Hash Join cost path.

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 the query optimizer uses streams.
  • off indicates the query optimizer does not use streams.

Default value: off

best_agg_plan

Parameter description: The query optimizer generates three plans for the aggregate operation under the stream:
  1. hashagg+gather(redistribute)+hashagg
  2. redistribute+hashagg(+gather)
  3. hashagg+redistribute+hashagg(+gather).

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

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.
  • Node group name (when 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.
  • Node Group name (when enable_nodegroup_debug is set to on): A specific Node Group is used as the computing Node Group.

Default value: query

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

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

Parent topic: Query Planning