Help Center/ GaussDB/ Developer Guide(Centralized_3.x)/ Configuring Running Parameters/ GUC Parameters/ Query Planning/ Other Optimizer Options
Updated on 2024-05-07 GMT+08:00
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Other Optimizer Options

cost_model_version

Parameter description: Specifies the version of the optimizer cost model. It can be regarded as a protection parameter to disable the latest optimizer cost model and keep consistent with the plan of the earlier version. If the value of this parameter is changed, many SQL plans may be changed. Therefore, exercise caution when performing this operation.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: 0, 1, 2, or 3

  • 0 indicates that the latest cost estimation model is used. The current version is equivalent to 3.
  • 1 indicates that the original cost estimation model is used.
  • 2: indicates that the enhanced COALESCE expression, hash join cost, and semi/anti join cost are used for estimation on the basis of 1.
  • 3: indicates that the boundary correction estimator is used to estimate the NDV on the basis of 2. The hint of indexscan can be applied to indexonlyscan.

Default value: 0

explain_dna_file

Parameter description: Sets explain_perf_mode to run to export object files in CSV format.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

The value of this parameter must be an absolute path plus a file name with the extension .csv.

Value range: a string

Default value: empty

explain_perf_mode

Parameter description: Specifies the display format of the explain command.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: normal, pretty, summary, and run

  • normal indicates that the default printing format is used.
  • pretty indicates a new format improved by using GaussDB. The new format contains a plan node ID, directly and effectively analyzing performance.
  • summary indicates that the analysis result on this information is printed in addition to the printed information specified by pretty.
  • run indicates that the system exports the printed information specified by summary as a CSV file for further analysis.

The display sequence may vary greatly according to the display format of explain. The examples of the normal and pretty formats are described as follows:

Example of the normal format:

                                                                                 QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Sort  (cost=21.23..21.23 rows=1 width=306)
   Sort Key: supplier.s_suppkey
   CTE revenue
     ->  HashAggregate  (cost=12.88..12.88 rows=1 width=76)
           Group By Key: lineitem.l_suppkey
           ->  Partition Iterator  (cost=0.00..12.87 rows=1 width=44)
                 Iterations: 7
                 ->  Partitioned Seq Scan on lineitem  (cost=0.00..12.87 rows=1 width=44)
                       Filter: ((l_shipdate >= '1996-01-01 00:00:00'::timestamp(0) without time zone) AND (l_shipdate < '1996-04-01 00:00:00'::timestamp without time zone))
                       Selected Partitions:  1..7
   InitPlan 2 (returns $3)
     ->  Aggregate  (cost=0.02..0.03 rows=1 width=64)
           ->  CTE Scan on revenue  (cost=0.00..0.02 rows=1 width=32)
   ->  Nested Loop  (cost=0.00..8.30 rows=1 width=306)
         ->  CTE Scan on revenue  (cost=0.00..0.02 rows=1 width=40)
               Filter: (total_revenue = $3)
         ->  Partition Iterator  (cost=0.00..8.27 rows=1 width=274)
               Iterations: 7
               ->  Partitioned Index Scan using supplier_s_suppkey_idx on supplier  (cost=0.00..8.27 rows=1 width=274)
                     Index Cond: (s_suppkey = revenue.supplier_no)
                     Selected Partitions:  1..7
(21 rows)

Example of the pretty format:

 id |                                  operation                                   | E-rows | E-width |    E-costs
----+------------------------------------------------------------------------------+--------+---------+----------------
  1 | ->  Sort                                                                     |      1 |     306 | 21.230..21.235
  2 |    ->  Nested Loop (3,9)                                                     |      1 |     306 | 0.000..8.303
  3 |       ->  CTE Scan on revenue                                                |      1 |      40 | 0.000..0.022
  4 |    ->  HashAggregate  [3, CTE revenue]                                       |      1 |      76 | 12.875..12.885
  5 |       ->  Partition Iterator                                                 |      1 |      44 | 0.000..12.865
  6 |          ->  Partitioned Seq Scan on lineitem                                |      1 |      44 | 0.000..12.865
  7 |    ->  Aggregate  [4, InitPlan 2 (returns $3)]                               |      1 |      64 | 0.022..0.033
  8 |       ->  CTE Scan on revenue                                                |      1 |      32 | 0.000..0.020
  9 |       ->  Partition Iterator                                                 |      1 |     274 | 0.000..8.270
 10 |          ->  Partitioned Index Scan using supplier_s_suppkey_idx on supplier |      1 |     274 | 0.000..8.270
(10 rows)

                                                         Predicate Information (identified by plan id)
---------------------------------------------------------------------------------------------------------------------------------------------------------------
   5 --Partition Iterator
         Iterations: 7
   6 --Partitioned Seq Scan on lineitem
         Filter: ((l_shipdate >= '1996-01-01 00:00:00'::timestamp(0) without time zone) AND (l_shipdate < '1996-04-01 00:00:00'::timestamp without time zone))
         Selected Partitions:  1..7
   3 --CTE Scan on revenue
         Filter: (total_revenue = $3)
   9 --Partition Iterator
         Iterations: 7
  10 --Partitioned Index Scan using supplier_s_suppkey_idx on supplier
         Index Cond: (s_suppkey = revenue.supplier_no)
         Selected Partitions:  1..7
(12 rows)

Note: The plan blocks in the preceding two formats are different display formats of the same plan. In the pretty format, the parts in bold are the CET and InitPlan plan blocks, which may be inserted in the middle of the Join connection block. When reading the Join block, skip the CTE and InitPlan blocks to find the internal table of the corresponding Join block.

Default value: pretty

analysis_options

Parameter description: Specifies whether to enable function options in the corresponding options to use the corresponding location functions, including data verification and performance statistics. For details, see the options in the value range.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: a string

  • HASH_CONFLICT indicates that the log in the pg_log directory of the database node process displays the statistics of the hash table, including the hash table size, hash link length, and hash conflict.
  • STREAM_DATA_CHECK indicates that a CRC check is performed on data before and after network data transmission.

Default value: ALL,on(),off(HASH_CONFLICT,STREAM_DATA_CHECK), which indicates that no location function is enabled.

cost_param

Parameter description: Specifies use of different estimation methods in specific customer scenarios, allowing estimated values approximating to onsite values. This parameter can control various methods simultaneously by performing AND (&) on the bit of each method. A method is selected if the result value is not 0.

When cost_param & 1 is set to a value other than 0, an improved mechanism is used for connecting the selection rate of non-equi-joins. This method is more accurate for estimating the selection rate of joins between two identical tables. At present, cost_param & 1=0 is not used. That is, a better formula is selected for calculation.

When cost_param & 2 is set to a value other than 0, the selection rate is estimated based on multiple filter criteria. The lowest selection rate among all filter criteria, but not the product of the selection rates for two tables under a specific filter criterion, is used as the total selection rate. This method is more accurate when a close correlation exists between the columns to be filtered.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 0 to INT_MAX

Default value: 0

var_eq_const_selectivity

Parameter description: Determines whether to use the new selection rate model to estimate the integer const selection rate.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the new selection rate model is used to calculate the selection rate of the integer const.
    • If an integer does not fall into the MCV, is not NULL, but falls into the histogram, the left and right boundaries of the histogram are used for estimation. If the integer does not fall into the histogram, the number of rows in the table is used for estimation.
    • If the integer is NULL or falls into the MCV, the original logic is used to calculate the selection rate.
  • off indicates that the original selection rate calculation model is used.

Default value: off

enable_partitionwise

Parameter description: Specifies whether to select an intelligent algorithm for joining partition tables.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that an intelligent algorithm is selected.
  • off indicates that an intelligent algorithm is not selected.

Default value: off

partition_page_estimation

Parameter description: Determines whether to optimize the estimation of partitioned table pages based on the pruning result.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the pruning result is used to optimize the page estimation.
  • off indicates that the pruning result is not used to optimize the page estimation.

Default value: off

partition_iterator_elimination

Parameter description: Determines whether to eliminate the partition iteration operator to improve execution efficiency when the partition pruning result of a partitioned table is a partition.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the partition iteration operator is eliminated.
  • off indicates that the partition iteration operator is not eliminated.

Default value: off

enable_functional_dependency

Parameter description: Determines whether the statistics about multiple columns generated by ANALYZE contain function dependency statistics and whether the function dependency statistics are used to calculate the selection rate.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates the following functions: 1. The statistics about multiple columns generated by ANALYZE contain function dependency statistics. 2. Function dependency statistics are used to calculate the selection rate.
  • off indicates the following functions: 1. The statistics about multiple columns generated by ANALYZE do not contain function dependency statistics. 2. Function dependency statistics are not used to calculate the selection rate.

Default value: off

rewrite_rule

Parameter description: Specifies the rewriting rule for enabled optional queries. Some query rewrite rules are optional. Enabling them cannot always improve the query efficiency. In a specific customer scenario, you can set the query rewriting rules through this GUC parameter to achieve optimal query efficiency.

This parameter can control the combination of query rewriting rules, for example, there is more than one override rule: rule1, rule2, rule3, and rule4. You can perform the following settings:

set rewrite_rule=rule1;          -- Enable query rewriting rule rule1
set rewrite_rule=rule2, rule3;     -- Enable the query rewriting rules rule2 and rule3
set rewrite_rule=none;         -- Disable all optional query rewriting rules

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: a string

  • none: Does not use any optional query rewriting rules.
  • lazyagg: Uses the Lazy Agg query rewriting rules for eliminating aggregation operations in subqueries.
  • magicset: The Magic Set query rewriting rules are used to associate subqueries which have aggregation operators with the main query in advance to reduce repeated scanning of sublinks.
  • uniquecheck: Uses the Unique Check query rewriting rules. Optimize the subquery statements in target columns without agg and check whether the number of returned rows is 1.
  • intargetlist: Uses the In Target List query rewriting rules (subquery optimization in the target column).
  • predpushnormal: Uses the Predicate Push query rewriting rule (push the predicate condition to the subquery).
  • predpushforce: Uses the Predicate Push query rewriting rules. Push down predicate conditions to subqueries and use indexes as much as possible for acceleration.
  • predpush: Selects the optimal plan based on the cost in predpushnormal and predpushforce.
  • disable_pullup_expr_sublink: The optimizer is not allowed to pull up sublinks of the expr_sublink type. For details about sublink classification and pull-up principles, see section "SQL Tuning Guide > Typical SQL Tuning Methods > Subquery Tuning" in Developer Guide.
  • enable_sublink_pullup_enhanced: Enhanced sublink query rewriting rules are used, including unrelated sublink pull-up of the WHERE and HAVING clauses and WinMagic rewriting optimization.
  • disable_pullup_not_in_sublink: The optimizer is not allowed to pull up sublinks related to NOT IN. For details about sublink classification and pull-up principles, see section "SQL Tuning Guide > Typical SQL Tuning Methods > Subquery Tuning" in Developer Guide.

Default value: magicset

The partialpush and disablerep parameters can be set but do not take effect.

enable_pbe_optimization

Parameter description: Specifies whether the optimizer optimizes the query plan for statements executed in Parse Bind Execute (PBE) mode.

This parameter is a SUSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the optimizer optimizes the query plan of the PBE statement.
  • off indicates that the optimization is not used.

Default value: on

enable_global_plancache

Parameter description: Specifies whether to share the cache for the execution plans of statements in PBE queries and stored procedures. Enabling this function can reduce the memory usage of database nodes in high concurrency scenarios.

When enable_global_plancache is enabled, the default value of local_syscache_threshold is greater than or equal to 16 MB to ensure that GPC takes effect. If the value of local_syscache_threshold is less than 16 MB, set it to 16 MB. If the value is greater than 16 MB, do not change it.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that cache sharing is enabled for the execution plans of statements in PBE queries and stored procedures.
  • off indicates no sharing.

Default value: off

gpc_clean_timeout

Parameter description: When enable_global_plancache is set to on, if a plan in the shared plan list is not used within the period specified by gpc_clean_timeout, the plan will be deleted. This parameter is used to control the retention period of a shared plan that is not used.

This is a SIGHUP parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 300 to 86400

  • The unit is second.

Default value: 1800, that is, 30 minutes

enable_global_stats

This parameter has been discarded in the current version. Do not set it.

enable_opfusion

Parameter description: Specifies whether to optimize simple addition, deletion, modification, and query operations.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

The restrictions on simple query are as follows:

  • Only indexscan and indexonlyscan are supported, and the filter criteria of all WHERE statements are on indexes.
  • Only single tables can be added, deleted, modified, and queried. Join and using are not supported.
  • Only row-store tables are supported. Partitioned tables and tables with triggers are not supported.
  • Information statistics features such as active sql and QPS are not supported.
  • Tables that are being scaled out or in are not supported.
  • The system column cannot be queried or modified.
  • Only simple SELECT statements are supported. For example: 
    SELECT c3 FROM t1 WHERE c1 = ? and c2 =10;

    Only columns in the target table can be queried. Columns c1 and c2 are index columns, which can be followed by constants or parameters. You can use for update.

  • Only simple INSERT statements are supported. For example: 
    INSERT INTO t1 VALUES (?,10,?);

    Only one VALUES is supported. The type in VALUES can be a constant or a parameter. RETURNING is not supported.

  • Only simple DELETE statements are supported. For example: 
    DELETE FROM t1 WHERE c1 = ? and c2 = 10;

    Columns c1 and c2 are index columns, which can be followed by constants or parameters.

  • Only simple UPDATE statements are supported. For example: 
    UPDATE t1 SET c3 = c3+? WHERE c1 = ? and c2 = 10;

    The values modified in column c3 can be constants, parameters, or a simple expression. Columns c1 and c2 are index columns, which can be followed by constants or parameters.

Value range: Boolean

  • on: enabled.
  • off: disabled.

Default value: on

enable_partition_opfusion

Parameter description: If this parameter is enabled when the enable_opfusion parameter is enabled, the simple query of the partitioned table can be optimized to improve the SQL execution performance. When the enable_global_plancache parameter is enabled, this parameter does not take effect even if it is set to on.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on: enabled.
  • off: disabled.

Default value: off

sql_beta_feature

Parameter description: Specifies the SQL engine's optional beta features to be enabled, including optimization of row count estimation and query equivalence estimation.

These optional features provide optimization for specific scenarios, but performance deterioration may occur in some scenarios for which testing is not performed. In a specific customer scenario, you can set the query rewriting rules through this GUC parameter to achieve optimal query efficiency.

This parameter determines the combination of the SQL engine's beta features, for example, feature1, feature2, feature3, and feature4. You can perform the following settings:

-- Enable beta feature feature1 of the SQL engine.
set sql_beta_feature=feature1;
-- Enable beta features feature2 and feature3 of the SQL engine.
set sql_beta_feature=feature2,feature3;
-- Disable all optional beta features of the SQL engine.
set sql_beta_feature=none;

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: a string

  • none: None of the beta optimizer features are used.
  • sel_semi_poisson: Uses poisson distribution to calibrate the equivalent semi-join and anti-join selection rates.
  • sel_expr_instr: Uses the matching row count to provide more accurate estimation for instr(col, 'const') > 0, = 0, = 1.
  • param_path_gen: Generates more possible parameterized paths.
  • rand_cost_opt: Optimizes the random read cost of tables that have a small amount of data.
  • param_path_opt: Uses the bloat ratio of the table to optimize the analysis information of indexes.
  • page_est_opt: Optimizes the relpages estimation for the analysis information of table indexes.
  • no_unique_index_first: Disables optimization of the primary key index scanning path first.
  • join_sel_with_cast_func: Type conversion functions are supported when the number of join rows is estimated.
  • canonical_pathkey: The regularization pathkey is generated in advance. (pathkey: a set of ordered key values of data.)

    After this parameter is enabled, the semantics of the output data of statements such as ORDER BY may be different from that of the standard ones in the case of outer join. Contact Huawei engineers to determine whether to enable this parameter.

  • index_cost_with_leaf_pages_only: Considers index leaf nodes when the index cost is estimated.
  • partition_opfusion: Enables partitioned table optimization.
  • a_style_coerce: enables the Decode type conversion rule to be compatible with O. For details, see the part related to case processing in ORA compatibility mode in section "SQL Reference > Type Conversion > UNION, CASE, and Related Constructs" in Developer Guide.
  • partition_fdw_on: SQL statements can be created for Postgres foreign tables based on partitioned tables.
  • predpush_same_level: Enables the predpush hint to control parameterized paths at the same layer.
  • enable_plsql_smp: Enables parallel execution of queries in stored procedures. Currently, only one query can be executed in parallel at a time, and no parallel execution plan is generated for cursor-related operations, autonomous transactions, and queries in exceptions.
  • disable_bitmap_cost_with_lossy_pages: Disables the computation of the cost of lossy pages in the bitmap path cost.
  • enable_upsert_execute_gplan: In the PBE scenario, if the UPDATE clause in the on duplicate key update statement contains parameters, set enable_upsert_execute_gplan to allow execution through gplan.
  • disable_merge_append_partition: Do not generate the Merge Append path for partitioned tables.

Default value: "sel_semi_poisson,sel_expr_instr,rand_cost_opt,param_path_opt,page_est_opt"

ngram_gram_size

Parameter description: Specifies the length of the ngram parser segmentation.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 1 to 4

Default value: 2

ngram_grapsymbol_ignore

Parameter description: Specifies whether the ngram parser ignores graphical characters.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on: The ngram parser ignores graphical characters.
  • off: The ngram parser does not ignore graphical characters.

Default value: off

ngram_punctuation_ignore

Parameter description: Specifies whether the ngram parser ignores punctuation marks.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on: The ngram parser ignores punctuation marks.
  • off: The ngram parser does not ignore punctuation marks.

Default value: on

default_statistics_target

Parameter description: Specifies the default statistics target for table columns without a column-specific target set via ALTER TABLE SET STATISTICS. If this parameter is set to a positive number, it indicates the number of samples of statistics information. If this parameter is set to a negative number, percentage is used to set the statistic target. The negative number converts to its corresponding percentage, for example, -5 means 5%.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from –100 to 10000

  • A larger positive number than the default value increases the time required to do ANALYZE, but might improve the quality of the optimizer's estimates.
  • Changing settings of this parameter may result in performance deterioration. If query performance deteriorates, you can:
    1. Restore to the default statistics.
    2. Use hints to force the optimizer to use the optimal query plan. For details, see section "SQL Tuning Guide > Tuning Using Plan Hints" in Developer Guide.

Default value: 100

auto_statistic_ext_columns

Parameter description: Collects statistics about multiple columns based on the first K columns of the composite index in the data table. This GUC parameter indicates K. For example, if a composite index is (a, b, c, d, e) and the GUC parameter is set to 3, statistics about multiple columns are generated on columns (a, b) and (a, b, c). Multi-column statistics can make the optimizer estimate the cardinality more accurate when querying with combined conditions.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

  • The system catalog does not take effect.
  • The statistics take effect only when the types of all columns support the comparison functions '=' and '<'.
  • System pseudocolumns in indexes, such as tableoid and ctid, are not collected.
  • By default, distinct values, MCVs without NULL, and MCVs with NULL are collected. If the AI-based cardinality estimation parameter enable_ai_stats is enabled, MCVs are not collected. Instead, models for AI-based cardinality estimation are collected.
  • If the index for creating multi-column statistics is deleted and no other index contains the multi-column combination, the multi-column statistics will be deleted in the next ANALYZE operation.
  • If the value of this parameter decreases, the new index generates multi-column statistics based on the value of this parameter. The generated multi-column statistics that exceed the value of this parameter will not be deleted.
  • If you want to disable the multi-column statistics on a specific combination only, you can retain the value of this parameter and run the ALTER TABLE tablename disable statistics ((column list)) command to disable the statistics on multiple columns in a specific combination.

Value range: an integer ranging from 1 to 4 The value 1 indicates that statistics about multiple columns are not automatically collected.

Default value: 1

constraint_exclusion

Parameter description: Specifies the query optimizer's use of table constraints to optimize queries.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: enumerated values

  • on indicates that constraints for all tables are examined.
  • off indicates that constraints for any table are not examined.
  • partition indicates that only constraints for inheritance child tables and UNION ALL subqueries are examined.

    When constraint_exclusion is set to on, the optimizer compares query conditions with the table's CHECK constraints, and omits scanning tables for which the conditions contradict the constraints.

Default value: partition

Currently, constraint_exclusion is enabled by default only for cases that are often used to implement table partitioning. Turning this feature on for all tables imposes extra planning on simple queries, and provides no benefit for simple queries. If you have no partitioned tables, set it to off.

cursor_tuple_fraction

Parameter description: Specifies the optimizer's estimated fraction of a cursor's rows that are retrieved.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: a floating point number ranging from 0.0 to 1.0

Smaller values of this setting bias the optimizer towards using fast start plans for cursors, which will retrieve the first few rows quickly while perhaps taking a long time to fetch all rows. Larger values put more emphasis on the total estimated time. At the maximum setting of 1.0, cursors are planned exactly like regular queries, considering only the total estimated time and how soon the first rows might be delivered.

Default value: 0.1

from_collapse_limit

Parameter description: Specifies whether the optimizer merges sub-queries into upper queries based on the resulting FROM list. The optimizer merges sub-queries into upper queries if the resulting FROM list would have no more than this many items.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 1 to INT_MAX

Smaller values reduce planning time but may lead to inferior execution plans.

Default value: 8

join_collapse_limit

Parameter description: Specifies whether the optimizer rewrites JOIN constructs (except FULL JOIN) into lists of FROM items based on the number of the items in the result list.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 1 to INT_MAX

  • Setting this parameter to 1 prevents join reordering. As a result, the join order specified in the query will be the actual order in which the relations are joined. The query optimizer does not always choose the optimal join order. Therefore, advanced users can temporarily set this variable to 1, and then specify the join order they desire explicitly.
  • Smaller values reduce planning time but lead to inferior execution plans.

Default value: 8

plan_mode_seed

Parameter description: This is a commissioning parameter. Currently, it supports only OPTIMIZE_PLAN and RANDOM_PLAN. The value 0 (for OPTIMIZE_PLAN) indicates the optimized plan using the dynamic planning algorithm. Other values are for RANDOM_PLAN, which indicates that the plan is randomly generated. –1 indicates that users do not specify the value of the seed identifier. In this case, the optimizer generates a random integer from 1 to 2147483647 and a random execution plan based on the generated integer. A GUC parameter value from 1 to 2147483647 is regarded as the seed identifier, based on which the optimizer generates a random execution plan.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from –1 to 2147483647

Default value: 0

  • If this parameter is set to RANDOM_PLAN, the optimizer generates a random execution plan that may not be the optimal one. Therefore, to guarantee the query performance, the default value 0 is recommended during upgrade, scale-out, scale-in, and O&M.
  • If this parameter is not set to 0, the specified plan hint will not be used.

hashagg_table_size

Parameter description: Specifies the hash table size during the execution of the HASH JOIN operation.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 0 to INT_MAX/2

Default value: 0

enable_bloom_filter

Parameter description: Specifies whether the BloomFilter optimization can be used. This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the BloomFilter optimization can be used.
  • off indicates that the BloomFilter optimization cannot be used.

Default value: on

enable_extrapolation_stats

Parameter description: Specifies whether the extrapolation logic is used for data of DATE type based on historical statistics. The logic can increase the accuracy of estimation for tables whose statistics are not collected in time, but will possibly provide an overlarge estimation due to incorrect extrapolation. Enable the logic only in scenarios where the data of DATE type is periodically inserted. This parameter is a SUSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the extrapolation logic is used for data of DATE type based on historical statistics.
  • off indicates that the extrapolation logic is not used for data of DATE type based on historical statistics.

Default value: off

autoanalyze

Parameter description: Specifies whether to automatically collect statistics on tables that have no statistics when a plan is generated. autoanalyze cannot be used for foreign or temporary tables. To collect statistics, manually perform the ANALYZE operation. If an exception occurs in the database during the execution of autoanalyze on a table, after the database is recovered, the system may still prompt you to collect the statistics of the table when you run the statement again. In this case, manually perform the ANALYZE operation on the table to synchronize statistics. This parameter is a SUSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the table statistics are automatically collected.
  • off indicates that the table statistics are not automatically collected.

Default value: off

This parameter does not take effect in centralized mode.

enable_analyze_check

Parameter description: Checks whether statistics were collected about tables whose reltuples and relpages are displayed as 0 in pg_class during plan generation.

This parameter is a SUSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the tables will be checked.
  • off indicates that the tables will not be checked.

Default value: off

enable_sonic_hashagg

Parameter description: Specifies whether to use the hash aggregation operator designed for column-oriented hash tables when certain constraints are met.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the hash aggregation operator designed for column-oriented hash tables is used when certain constraints are met.
  • off indicates that the hash aggregation operator designed for column-oriented hash tables is not used.
  • When the hash aggregation operator designed for column-oriented hash tables is used, the memory usage of the query can be reduced. However, in scenarios where the performance is significantly improved based on code generation, the performance of the operator may deteriorate.
  • If enable_sonic_hashagg is enabled and the Hash Agg operator designed based on the column-oriented hash table is used when the query meets the constraint condition, the operator is displayed as Sonic Hash Aggregation in the execution plan and execution information of Explain Analyze/Performance; when the query does not meet the constraint condition, the operator is displayed as Hash Aggregation. For details, see section "SQL Tuning Guide > Introduction to the SQL Execution Plan > Description" in Developer Guide.

Default value: on

enable_sonic_hashjoin

Parameter description: Specifies whether to use the hash join operator designed for column-oriented hash tables when certain constraints are met.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the hash join operator designed for column-oriented hash tables is used when certain constraints are met.
  • off indicates that the hash join operator designed for column-oriented hash tables is not used.
  • Currently, the parameter can be used only for Inner Join.
  • If enable_sonic_hashjoin is enabled, the memory usage of query using the Hash Inner operator can be reduced. However, in scenarios where the code generation technology can significantly improve performance, the performance of the operator may deteriorate.
  • If enable_sonic_hashjoin is enabled and the Hash Join operator designed based on the column-oriented hash table is used when the query meets the constraint condition, the operator is displayed as Sonic Hash Join in the execution plan and execution information of Explain Analyze/Performance; when the query does not meet the constraint condition, the operator is displayed as Hash Join. For details, see section "SQL Tuning Guide > Introduction to the SQL Execution Plan > Description" in Developer Guide.

Default value: on

enable_sonic_optspill

Parameter description: Specifies whether to optimize the number of files to be written to disks for the Hash Join operator designed for column-oriented hash tables. If this parameter is set to on, the number of files written to disks does not increase significantly when the Hash Join operator writes a large number of files to disks.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on indicates that the optimization is enabled.
  • off indicates that the optimization is disabled.

Default value: on

plan_cache_mode

Parameter description: Specifies the policy for generating an execution plan in the prepare statement.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: enumerated values

  • auto indicates that the custom plan or generic plan is selected by default.
  • force_generic_plan indicates that the generic plan (soft parse) is forcibly used. The generic plan is a plan generated after you run a prepared statement. The plan policy binds parameters to the plan when you run the EXECUTE statement and execute the plan. The advantage of this plan is that repeated optimizer overheads can be avoided in each execution. The disadvantage is that the plan may not be optimal when data skew occurs for the bound parameters and may result in poor plan execution performance.
  • force_custom_plan indicates that the custom plan (hard parse) is forcibly used. The custom plan is a plan generated after you run a prepared statement where parameters in the EXECUTE statement are embedded. The custom plan generates a plan based on specific parameters in the EXECUTE statement. This plan generates a preferred plan based on specific parameters each time and has good execution performance. The disadvantage is that the plan needs to be regenerated before each execution, resulting in a large amount of repeated optimizer overhead.

This parameter is valid only for prepared statements. It is used when the parameterized field in a prepared statement has severe data skew.

Default value: auto

enable_hypo_index

Parameter description: Determines whether the optimizer considers virtual indexes when executing the EXPLAIN command.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on: enabled.
  • off: disabled.

Default value: off

enable_auto_explain

Parameter description: Specifies whether to enable the function of automatically printing execution plans. This parameter is used to locate slow stored procedures or slow queries and is valid only for the currently connected primary database node.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean. The value true indicates that the function is enabled, and the value false indicates that the function is disabled.

Default value: false

auto_explain_level

Parameter description: Specifies the log level for automatically printing execution plans.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: enumerated type. The value can be LOG or NOTICE. LOG indicates that the execution plan is printed in logs. NOTICE indicates that the execution plan is printed in notification mode.

Default value: LOG

auto_explain_log_min_duration

Parameter description: Specifies the minimum duration of execution plans that are automatically printed. Only execution plans whose duration is greater than the value of auto_explain_log_min_duration will be printed.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 0 to 2147483647. The unit is ms.

  • 0: All executed plans are printed.
  • 3000: All execution plans will be printed if the execution of a statement takes more than 3000 ms.

Default value: 0

query_dop

Parameter description: Specifies the user-defined degree of parallelism (DOP). This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 1 to 64 If the fixed SMP function is enabled, the system uses the fixed DOP.

After enabling concurrent queries, ensure you have sufficient CPU, memory, and network to achieve the optimal performance.

Default value: 1

enable_startwith_debug

Parameter description: Specifies whether to enable the start with or connect by parameter for debugging. If this parameter is enabled, information about all tail columns related to the start with feature is displayed.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean. The value true indicates that the function is enabled, and the value false indicates that the function is disabled.

Default value: false

enable_inner_unique_opt

Parameter description: Specifies that Inner Unique is optimized for nested loop join, hash join, and sort merge join. That is, the number of matching times is reduced when the attribute corresponding to the inner table in the join condition meets the uniqueness constraint.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on: used.
  • off: not used.

Default value: on

enable_indexscan_optimization

Parameter description: Specifies whether to optimize B-tree index scanning (IndexScan and IndexOnlyScan) in the Astore engine.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on: used.
  • off: not used.

Default value: off

immediate_analyze_threshold

Parameter description: Specifies the threshold for automatically analyzing inserted data. When the amount of inserted data reaches the original data amount multiplied by the value of immediate_analyze_threshold, and the total number of rows exceeds 100, ANALYZE is automatically triggered.

This is a SIGHUP parameter. Set it based on instructions provided in Table 1.

Value range: an integer ranging from 0 to 1000 If this parameter is set to 0, this function is disabled.

Default value: 0.

  1. This function supports only permanent and unlogged tables. Temporary tables are not supported.
  2. ANALYZE is not automatically triggered twice within 10 seconds for the same table.

enable_dynamic_samplesize

Parameter description: Specifies whether to dynamically adjust the number of sampled rows. For a large table with more than one million rows, the number of sampled rows is dynamically adjusted during statistics collection to improve statistics accuracy.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1.

Value range: Boolean

  • on: indicates that this function is enabled.
  • off: indicates that the function is disabled.

Default value: on

The function of dynamically adjusting the number of sampled rows supports only absolute sampling.

Parent topic: Query Planning