索引使用的前提

首先，是前面提到的Access Method, 然后是使用的operator class, 以及opc中定义的operator或function；
其次，遵循CBO的选择
#seq_page_cost = 1.0
#random_page_cost = 4.0
#cpu_tuple_cost = 0.01
#cpu_index_tuple_cost = 0.005
#cpu_operator_cost = 0.0025
#effective_cache_size = 128MB
最后，遵循完CBO的选择, 还需要符合当前配置的Planner 配置
#enable_bitmapscan = on
#enable_hashagg = on
#enable_hashjoin = on
#enable_indexscan = on
#enable_material = on
#enable_mergejoin = on
#enable_nestloop = on
#enable_seqscan = on
#enable_sort = on
#enable_tidscan = on