Configuring Key Parameters for SQL Optimization

enable_nestloop=off

Specifies how the optimizer uses nested-loop join. If this parameter is set to on, the optimizer preferentially uses nested-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. Generally, among the three join modes (Nested Loop, Merge Join, and Hash Join), Nested Loop is applicable to scenarios with small data volume or indexes, and Hash Join is applicable to big data analysis scenarios.

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_fast_query_shipping=on

Specifies whether the optimizer uses a distribution framework to execute quick execution plans. If the value is on, the execution plan is generated on both CNs and DNs. If the value is off, the distribution framework is used, that is, the execution plan is generated on the CN and then sent to the DN for execution.

1

SET enable_fast_query_shipping to off;

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.

enable_broadcast=on

Specifies whether the optimizer uses data broadcast. In data broadcast, a large amount of data is transferred on the network. When the number of transmission nodes (stream) is large and the estimation is inaccurate, set this parameter to off and check whether the performance is improved.

rewrite_rule

Specifies whether the optimizer enables the rewriting rules LAZYAGG, MAGICSET, PARTIALPUSH, UNIQUECHECK, DISABLEREP, INTARGETLIST, PREDPUSHNORMAL, PREDPUSHFORCE, PREDPUSH, DISABLE_PULLUP_EXPR_SUBLINK, DISABLE_PULLUP_NOT_IN_SUBLINK, and ENABLE_SUBLINK_PULLUP_ROWNUM.

sql_beta_feature

Specifies whether the optimizer enables the beta features of SEL_SEMI_POISSON, NO_UNIQUE_INDEX_FIRST, JOIN_SEL_WITH_CAST_FUNC, SEL_EXPR_INSTR, PARAM_PATH_GEN, RAND_COST_OPT, PARAM_PATH_OPT, PAGE_EST_OPT, CANONICAL_PATHKEY, INDEX_COST_WITH_INDEX_COST_WITH_LEAF_PAGES_ONLY, PREDPUSH_SAME_LEVEL, PARTITION_FDW_ON, and DISABLE_BITMAP_COST_WITH_LOSSY_PAGES.