SELECT HINT

Function

SELECT HINT sets GUC parameters related to query optimization that take effect during the query execution. This section describes the enhanced SELECT HINT syntax of Dolphin. For details about the hints supported by the kernel, see Plan Hint Optimization.

Syntax

set_var(param = value)

Parameters

• param

  Parameter name.

  Currently, the following parameters can be set and take effect by using hints:

  • Boolean

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

  • Integer

    query_dop

  • Floating point

    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

    try_vector_engine_strategy

  • Character string

    dolphin.optimizer_switch

• value

  Value of a parameter.