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 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_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
In clusters prior to 8.1.3.333, this parameter is automatically enabled. However, in newly installed 8.1.3.333 clusters, this parameter is disabled by default. In upgrade scenarios, this parameter is forward compatible, meaning that its default value remains the same as the cluster's default value before the upgrade.
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
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
best_agg_plan
- hashagg+gather(redistribute)+hashagg
- redistribute+hashagg(+gather)
- 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.
- 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
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