Configuring Key Parameters for SQL Optimization

enable_nestloop=off

Specifies how the optimizer uses Nest Loop Join. If this parameter is set to on, the optimizer preferentially uses Nest Loop Join. If it is set to off, the optimizer preferentially uses other methods, if any.

1

SET enable_nestloop to off;

Disabling this parameter does not affect the index nested-loop join operator (corresponding to the enable_index_nestloop parameter). During real-world optimization, it is important to assess whether to disable this parameter based on the specific circumstances. Three types of joins are supported: nested loops, merge joins, and hash joins. Specifically, nested loops are best suited for scenarios with small data volumes or indexes, while hash joins are ideal for big data analysis.

enable_index_nestloop=on

Specifies whether to enable the index nested-loop join operator.

1

SET enable_index_nestloop to off;

Differences between enable_index_nestloop and enable_nestloop: enable_index_nestloop helps manage scenarios where the inner table undergoes index scans, and the outer table supplies index condition parameters for the inner table.

enable_bitmapscan=on

Specifies whether the optimizer uses bitmap scan. If the value is on, bitmap scan is used. If the value is off, it is not used.

1

SET enable_bitmapscan to off;

The bitmap scan applies only in the query condition where a > 1 and b > 1 and indexes are created on columns a and b. However, the performance of bitmapscan is sometimes inferior to that of indexscan. During optimization, if the query performance is poor and bitmapscan operators are in the execution plan, set this parameter to off and check whether the performance is improved.

enable_hashagg=on

Specifies whether the optimizer uses hash aggregate plans.

enable_hashjoin=on

Specifies whether the optimizer uses hash join plans.

enable_mergejoin=on

Specifies whether the optimizer uses merge join plans.

enable_indexscan=on

Specifies whether the optimizer uses index scan plans.

enable_indexonlyscan=on

Specifies whether the optimizer uses index-only scan plans.

enable_seqscan=on

Specifies whether the optimizer uses sequential scan plans. It is impossible to suppress sequential scans entirely, but setting this variable to off encourages the optimizer to choose other methods if available.

enable_sort=on

Specifies the optimizer sorting order. It is impossible to fully suppress explicit sorting, but setting this variable to off encourages the optimizer to choose other methods if available.

rewrite_rule

Specifies whether the optimizer enables the LAZYAGG, MAGICSET, PARTIALPUSH, DISABLEREP, UNIQUECHECK, INTARGETLIST, PREDPUSH, PREDPUSHFORCE, PREDPUSHNORMAL, DISABLE_PULLUP_EXPR_SUBLINK, ENABLE_SUBLINK_PULLUP_ENHANCED, DISABLE_PULLUP_NOT_IN_SUBLINK, DISABLE_ROWNUM_PUSHDOWN, DISABLE_WINDOWAGG_PUSHDOWN rewriting, or GROUPBY_PUSHDOWN_SUBQUERY rule.

sql_beta_feature

Specifies whether the optimizer enables the SEL_SEMI_POISSON, SEL_EXPR_INSTR, PARAM_PATH_GEN, RAND_COST_OPT, PARAM_PATH_OPT, PAGE_EST_OPT, CANONICAL_PATHKEY, PREDPUSH_SAME_LEVEL, PARTITION_FDW_ON, DISABLE_BITMAP_COST_WITH_LOSSY_PAGES, ENABLE_UPSERT_EXECUTE_GPLAN, or DISABLE_FASTPATH_INSERT beta feature.

var_eq_const_selectivity

Specifies whether the optimizer uses histograms to calculate the selectivity of integer constants.

partition_page_estimation

Specifies whether to optimize page estimation of partitioned table pages based on the pruning result. Only the partitioned table pages and local index pages are included. The global index pages are not included. The estimation formula is as follows:

Number of pages after estimation = Total number of pages in the partitioned table x (Number of partitions after pruning/Total number of partitions)

partition_iterator_elimination

Specifies whether to eliminate the partition iteration operators to improve execution efficiency when the partition pruning result of a partitioned table is a partition.

enable_functional_dependency

Specifies whether functional dependency statistics are used.

Setting this parameter to on will enable the following functions:

1. The statistics about multiple columns generated by ANALYZE contain functional dependency statistics.
2. Function dependency statistics are used to calculate the selectivity.

Setting this parameter to off will disable the following functions:

1. The statistics about multiple columns generated by ANALYZE do not contain functional dependency statistics.
2. Function dependency statistics are not used to calculate the selectivity.

Functional dependency statistics are applicable to the where a = 1 and b = 1 condition, in which a and b must be attributes of the same table subject to equivalent constraints and the constraints are connected by AND. There are at least two constraints.

enable_seqscan_fusion

Specifies whether to enable the sequential scan noise floor elimination function.

enable_inner_unique_opt

Specifies whether the optimizer uses Inner Unique.