Question

我有一个gps跟踪应用程序。它有一个名为gps_vehicle_data的表，其中经常存储传入的gps数据。我频繁地查询该表来处理它，因为它只包含原始数据。最近，我目睹了在桌面上执行select语句的长时间延迟。以下是EXPLAIN的结果。我也试过做VACUUM＆amp;粘贴下面的结果。可能是什么原因？

EXPLAIN (ANALYZE, BUFFERS) select * from gps_vehicle_data;

                                                           QUERY PLAN                                                            
---------------------------------------------------------------------------------------------------------------------------------
 Seq Scan on gps_vehicle_data  (cost=0.00..130818.81 rows=1400881 width=1483) (actual time=209.129..62488.822 rows=9635 loops=1)
   Buffers: shared hit=13132 read=103678 dirtied=67 written=25
 Planning time: 0.050 ms
 Execution time: 62500.850 ms

VACUUM OUTPUT。

VACUUM (VERBOSE,ANALYSE) gps_vehicle_data;
INFO:  vacuuming "public.gps_vehicle_data"
INFO:  index "gps_vehicle_data_pkey" now contains 1398939 row versions in 10509 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.07s/0.09u sec elapsed 9.38 sec.
INFO:  index "gps_vehicle_data_status_idx" now contains 1398939 row versions in 4311 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.03s/0.04u sec elapsed 4.50 sec.
INFO:  index "gps_vehicle_data_url_data_idx" now contains 1399004 row versions in 98928 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.76s/0.88u sec elapsed 82.74 sec.
INFO:  index "gps_vehicle_data_createdon_idx" now contains 1399007 row versions in 3946 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.02u sec elapsed 1.92 sec.
INFO:  "gps_vehicle_data": found 0 removable, 1402484 nonremovable row versions in 116884 out of 116884 pages
DETAIL:  1401490 dead row versions cannot be removed yet.
There were 143431 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 1.70s/2.38u sec elapsed 200.61 sec.
INFO:  vacuuming "pg_toast.pg_toast_17296"
INFO:  index "pg_toast_17296_index" now contains 0 row versions in 1 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.01 sec.
INFO:  "pg_toast_17296": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.01 sec.
INFO:  analyzing "public.gps_vehicle_data"
INFO:  "gps_vehicle_data": scanned 30000 of 116884 pages, containing 335 live rows and 359656 dead rows; 335 rows in sample, 1042851 estimated total rows
VACUUM

Answer 1

你读取超过100000个块来获得大约10000行，这意味着你的表几乎完全没有任何东西（它正在遭受 table bloat ）。

该表必须在某个时间包含更多数据，并且大部分数据已被删除，这导致了膨胀。

正如@a_horse_with_no_name所提到的，有些行无法回收，因为有一些旧事务会阻止它们，但是VACUUM将释放死行，它不会重新组织表以消除膨胀。< / p>

在这种情况下，正确的解决方案是使用VACUUM (FULL, ANALYZE) gps_vehicle_data（ANALYZE只是为了很好的衡量，因为看起来你的表统计信息已关闭），这将重新组织表。但是，请注意，VACUUM (FULL)正在运行时，对表的所有访问都会被阻止。

Postgres表选择查询太慢了

1 个答案: