SELECT HINT

Function

Set the GUC parameters related to query optimization that are in effect within this query execution. This section deals with dolphin's syntactic enhancements to select-hint. For details on kernel-supported hints, see Hint-based Tuning.

Syntax

set_var(param = value)

Parameter Description

• param

  Parameter name.

  The following parameters are currently supported to take effect using the Hint setting

  • Boolean type:

    enable_bitmapscan, enable_hashagg，enable_hashjoin, enable_indexscan，enable_indexonlyscan, enable_material，enable_mergejoin, enable_nestloop，enable_index_nestloop, enable_seqscan，enable_sort, enable_tidscan，partition_iterator_elimination，partition_page_estimation，enable_functional_dependency，var_eq_const_selectivity,

  • Integer type:

    query_dop

  • Floating point type:

    cost_weight_index、default_limit_rows、seq_page_cost、random_page_cost、cpu_tuple_cost、cpu_index_tuple_cost、cpu_operator_cost、effective_cache_size

  • Enumeration type:

    try_vector_engine_strategy

  • String type:

    dolphin.optimizer_switch

• value

  The value of the parameter.