track_io_timing

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• 9.6
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• 9.3
• 9.2

将 track_io_timing 与 EXPLAIN 一起使用

postgres=# SET track_io_timing = ON;
SET

postgres=# EXPLAIN (BUFFERS, ANALYZE) SELECT COUNT(*) FROM object;
                                                  QUERY PLAN                                                  
--------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=87.40..87.41 rows=1 width=8) (actual time=48.855..48.874 rows=1 loops=1)
   Buffers: shared read=30
   I/O Timings: read=1.411
   ->  Seq Scan on object  (cost=0.00..75.92 rows=4592 width=0) (actual time=0.338..25.602 rows=4477 loops=1)
         Buffers: shared read=30
         I/O Timings: read=1.411
 Planning Time: 5.024 ms
 Execution Time: 49.186 ms
(8 rows)

请注意，在执行上述查询后，数据将被缓存，再次执行将不涉及 I/O，并且 EXPLAIN 输出中不会包含 "I/O Timings" 值。

postgres=# EXPLAIN (BUFFERS, ANALYZE) SELECT COUNT(*) FROM object;
                                                  QUERY PLAN                                                  
--------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=87.40..87.41 rows=1 width=8) (actual time=53.178..53.196 rows=1 loops=1)
   Buffers: shared hit=30
   ->  Seq Scan on object  (cost=0.00..75.92 rows=4592 width=0) (actual time=0.043..26.705 rows=4477 loops=1)
         Buffers: shared hit=30
 Planning Time: 0.174 ms
 Execution Time: 53.295 ms
(6 rows)

尝试以非超级用户的身份设置 track_io_timing

postgres=*> SET track_io_timing TO on;
ERROR:  permission denied to set parameter "track_io_timing"

• PostgreSQL 文档: track_io_timing

• track_io_timing - malisper 于 2017 年 6 月的文章