摘要

關(guān)系數(shù)據(jù)庫(kù)很重要的一個(gè)方面是查詢速度。查詢速度的好壞，直接影響一個(gè)系統(tǒng)的好壞。

查詢速度一般需要通過(guò)查詢規(guī)劃來(lái)窺視執(zhí)行的過(guò)程。

查詢路徑會(huì)選擇查詢代價(jià)最低的路徑執(zhí)行。而這個(gè)代價(jià)是怎么算出來(lái)的呢。

主要關(guān)注的參數(shù)和表

參數(shù):來(lái)自postgresql.conf文件，可以通過(guò)show 來(lái)查看

seq_page_cost = 1.0 # measured on an arbitrary scale
random_page_cost = 4.0 # same scale as above
cpu_tuple_cost = 0.01 # same scale as above
cpu_index_tuple_cost = 0.005 # same scale as above
cpu_operator_cost = 0.0025 # same scale as above
parallel_tuple_cost = 0.1 # same scale as above
parallel_setup_cost = 1000.0 # same scale as above