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_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
Important
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: on
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_redistribute¶
Parameter description: Controls whether the query optimizer uses the local redistribute or split redistribute distribution method when estimating the cost of streams. This parameter is supported only by clusters of version 8.2.1.300 or later.
Type: USERSET
Value range: Boolean
on indicates that either of the distribution methods is used.
off indicates that none of the distribution methods is used.
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¶
Parameter description: The query optimizer generates three plans for the aggregate operation under the stream:
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
index_selectivity_cost¶
Parameter description: controls the cost calculation (selection rate > 0.001) of cbtree during the scan of column-store table indexes. This parameter is supported only by clusters of version 8.2.1.100 or later.
Type: USERSET
Value range: a floating point, which can be -1 or ranges from 0 to 1000.
If this parameter is set to 0, the index selection rate is not affected by the threshold 0.001.
If the value is -1, the value is affected by disable_cost.
When it is set to other values, the value is the coefficient for cbtree cost calculation.
Default value: -1
index_cost_limit¶
Parameter description: threshold for disabling the cost calculation of cbtree during column-store table index scanning. This parameter is supported only by clusters of version 8.2.1.100 or later.
Type: USERSET
Value range: an integer ranging from 0 to 2147483647
If the value is 0, the parameter does not take effect.
If this parameter is set to other values and the number of rows in a table is less than the value of this parameter, the table is not affected by the index selection rate threshold 0.001.
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: an integer ranging from 0 to 3.
At value 3, in addition to the capabilities of value 2, inline CTEs can be pushed down if referenced only once. This value is supported only by clusters of version 8.2.1.105 or later.
At value 2, besides the features of value 1, pushdown is enabled for CTEs containing VOLATILE functions in the target column.
At value 1, along with the functionalities of value 0, the nextval, uuid_generate_v1, sys_guid, and uuid functions can be fully pushed down if they appear in the target column.
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: 3
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
Important
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.
Important
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
prefer_hashjoin_path¶
Parameter description: whether to preferentially generate hashjoin paths so that other paths with high costs can be pre-pruned to shorten the overall plan generation time. This parameter is supported only by clusters of version 8.2.1 or later.
Type: USERSET
Value range: Boolean
off: disables the optimizations generated in advance in the hashjoin path.
on: enables the optimizations generated in advance in the hashjoin path.
Default value: on
enable_hashfilter_test¶
Parameter description: whether to add hash filters to columns for base table scan to check whether the results meet expectations. In addition, this parameter determines whether to check the DN accuracy when data is inserted (that is, whether the current data should be inserted into the current DN). This parameter is supported only by clusters of version 8.2.1.300 or later.
Type: USERSET
Value range: Boolean
off indicates that hash filters are not added to columns for base table scan, and the DN accuracy is not verified during data insertion.
on indicates that hash filters are added to columns for base table scan, and the DN accuracy is verified during data insertion.
Default value: on
Important
This parameter is valid only for tables distributed in hash mode.
If this parameter is set to on, DN accuracy is verified during data insertion, affecting data insertion performance.