Question

set cpu_tuple_cost=0.01;  
set cpu_index_tuple_cost = 0.005;  
set cpu_operator_cost = 0.0025;  
set seq_page_cost= 1.0;  
set random_page_cost = 4.0; 

set session enable_seqscan = off;
explain (analyze,verbose,costs,buffers,timing)select c_bh,c_xzdm,c_jgid,c_ajbm from t_test where d_slrq >='2018-03-18'

Bitmap Heap Scan on db.t_test  (cost=4.17..10.31 rows=3 width=96) (actual time=0.033..0.039 rows=5 loops=1)
  Output: c_bh, c_xzdm, c_jgid, c_ajbm
  Recheck Cond: (t_test.d_slrq >= '2018-03-18'::date)
  Heap Blocks: exact=2
  Buffers: shared hit=3
  ->  Bitmap Index Scan on idx_ttjaj_dslrq  (cost=0.00..4.17 rows=3 width=0) (actual time=0.014..0.014 rows=6 loops=1)
        Index Cond: (t_test.d_slrq >= '2018-03-18'::date)
        Buffers: shared hit=1
Planning time: 0.265 ms
Execution time: 0.079 ms

db_jcxx=# select relpages,reltuples from pg_class where relname ='t_test';
 relpages | reltuples 
----------+-----------
        7 |       141

db_jcxx=# select relpages,reltuples from pg_class where relname ='idx_ttjaj_dslrq';
 relpages | reltuples 
----------+-----------
        2 |       141

最终费用= 10.31是如何计算的？不知道我还需要提供更多信息吗？

postgresql：如何计算索引扫描的成本？

0 个答案: