postgresql psql explain選項使用示例介紹

postgresql psql explain選項使用示例介紹

explain

postgres=# explain select count(*) from pgbench_accounts ;
                                                   QUERY PLAN                                                    
-----------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=2854.29..2854.30 rows=1 width=8)
   ->  Index Only Scan using pgbench_accounts_pkey on pgbench_accounts  (cost=0.29..2604.29 rows=100000 width=0)
(2 rows)

postgres=#

explain analyze

postgres=# explain analyze select count(*) from pgbench_accounts ;
                                                                           QUERY PLAN                                                                            
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=2854.29..2854.30 rows=1 width=8) (actual time=26.809..26.809 rows=1 loops=1)
   ->  Index Only Scan using pgbench_accounts_pkey on pgbench_accounts  (cost=0.29..2604.29 rows=100000 width=0) (actual time=0.033..14.879 rows=100000 loops=1)
         Heap Fetches: 0
 Planning time: 0.099 ms
 Execution time: 26.877 ms
(5 rows)

explain (analyze,buffers)

聯合使用analyze和buffers選項

注意：buffers必須跟analyze一起使用，只用真實執行SQL才能獲取緩衝區信息），可通過實際執行SQL查看實際的代價和緩衝區命中的情況，

postgres=# explain (analyze,buffers) select count(*) from pgbench_accounts ;
                                                                           QUERY PLAN                                                                            
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=2854.29..2854.30 rows=1 width=8) (actual time=28.387..28.387 rows=1 loops=1)
   Buffers: shared hit=276
   ->  Index Only Scan using pgbench_accounts_pkey on pgbench_accounts  (cost=0.29..2604.29 rows=100000 width=0) (actual time=0.019..14.825 rows=100000 loops=1)
         Heap Fetches: 0
         Buffers: shared hit=276
 Planning time: 0.129 ms
 Execution time: 28.438 ms
(7 rows)

postgres=# 

explain (analyze,verbose,buffers,costs,timing)

postgres=# explain (analyze,verbose,buffers,costs,timing) select count(*) from pgbench_accounts ;
                                                                               QUERY PLAN                                                                               
------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=2854.29..2854.30 rows=1 width=8) (actual time=28.262..28.262 rows=1 loops=1)
   Output: count(*)
   Buffers: shared hit=276
   ->  Index Only Scan using pgbench_accounts_pkey on public.pgbench_accounts  (cost=0.29..2604.29 rows=100000 width=0) (actual time=0.019..14.475 rows=100000 loops=1)
         Output: aid
         Heap Fetches: 0
         Buffers: shared hit=276
 Planning time: 0.171 ms
 Execution time: 28.297 ms
(9 rows)

參考

1. explain (analyze,verbose,buffers,costs,timing) select
2. Postgresql explain的analyze和buffers選項