db_file_multiblock_read_count 对cost的影响-优快云博客

本文链接：https://blog.youkuaiyun.com/iteye_8576/article/details/82271796

db_file_multiblock_read_count = 32

実行計画
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   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=35 Card=1 Bytes=13)
   1    0   SORT (AGGREGATE)
   2    1     TABLE ACCESS (FULL) OF 'T1' (TABLE) (Cost=35 Card=9872 Bytes=128336)


db_file_multiblock_read_count = 16
実行計画
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=39 Card=1 Bytes=13)
   1    0   SORT (AGGREGATE)
   2    1     TABLE ACCESS (FULL) OF 'T1' (TABLE) (Cost=39 Card=9872 Bytes=128336)


db_file_multiblock_read_count = 8
実行計画
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=48 Card=1 Bytes=13)
   1    0   SORT (AGGREGATE)
   2    1     TABLE ACCESS (FULL) OF 'T1' (TABLE) (Cost=48 Card=9872 Bytes=128336)


db_file_multiblock_read_count = 4
実行計画
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=66 Card=1 Bytes=13)
   1    0   SORT (AGGREGATE)
   2    1     TABLE ACCESS (FULL) OF 'T1' (TABLE) (Cost=66 Card=9872 Bytes=128336)