目录
环境
系统平台：N/A
版本：4.1.1
症状
应用方反映业务量不大的情况下服务器负载较高，执行SQL的速度明显感觉缓慢。检查数据库TOP SQL，发现与表test有关，查看该表的统计值，live_tuple只有91966条，dead tuple为702346条。
| highgo=# select n_live_tup,n_dead_tup from pg_stat_all_tables where relname = 'test'; n_live_tup | n_dead_tup ------------+------------ 91966 | 702346 (1 row) |
手动对该表执行VACUUM同样无法回收dead tuple，报错如下：
| highgo=# vacuum(verbose,analyze) test; INFO: 00000: vacuuming "public.test" INFO: 00000: index "index_test_content_id" now contains 146076 row versions in 698 pages DETAIL: 0 index row versions were removed. 175 index pages have been deleted, 126 are currently reusable. CPU 0.00s/0.00u sec elapsed 0.00 sec. INFO: 00000: index "test_pkey" now contains 146076 row versions in 568 pages DETAIL: 0 index row versions were removed. 77 index pages have been deleted, 68 are currently reusable. CPU 0.00s/0.00u sec elapsed 0.00 sec. INFO: 00000: "test": found 0 removable, 789485 nonremovable row versions in 10178 out of 10276 pages DETAIL: 702346 dead row versions cannot be removed yet. There were 59707 unused item pointers. Skipped 0 pages due to buffer pins. 0 pages are entirely empty. CPU 0.04s/0.15u sec elapsed 0.20 sec. INFO: 00000: vacuuming "pg_toast.pg_toast_16737" INFO: 00000: index "pg_toast_16737_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 0.13 sec. INFO: 00000: "pg_toast_16737": 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 0.59 sec. INFO: 00000: analyzing "public.test" INFO: 00000: "test": scanned 10276 of 10276 pages, containing 90959 live rows and 702346 dead rows; 30000 rows in sample, 90959 estimated total row |
问题原因
当我们开启一个事务后，为了实现多版本的控制，数据库会阻止未结束的长事务之后产生的所有dead tuple,即使与该事务无关的其他表也是如此。
- Live transactions performing a write operation in any table will prevent vacuuming dead rows
generated by commited transactions that started after first live transaction in any other table.
详细的解决方案请登录【瀚高技术支持平台】查看
https://support.highgo.com/#/index/docContent/35b88a720452d610