PostgreSQL unlogged表

# \dt+ List of relations Schema | Name | Type | Owner | Size | Description --------------------------+------------------------+-------+----------+--------+------------- uber_geocoder_tw_15q3_v2 | compiling_info | table | postgres | 16 kB | uber_geocoder_tw_15q3_v2 | data_process_reports | table | postgres | 16 kB | uber_geocoder_tw_15q3_v2 | info | table | postgres | 16 kB | uber_geocoder_tw_15q3_v2 | twn_addr_compact | table | postgres | 774 MB | (4 rows) uber_geocoder=# \timing Timing is on.
uber_geocoder=# create table twn_addr_compact_loggod as select * from twn_addr_compact ; SELECT 258902 Time: 977250.581 ms

可以看到在新建正常表并插770M的数据的情况下耗时近16分钟

新建一张unlogged表并插入770M数据进行测试

uber_geocoder=# create unlogged table twn_addr_compact_unloggod as select * from twn_addr_compact ;
SELECT 258902
Time: 300683.321 ms

可以看到在同等条件下unlogged表的插入速度为5分钟，性能提高了三倍。

 感兴趣的可以将postgres进程kill掉，然后再启动数据库，就会发现我们刚才创建的unlogged表数据丢失。

如何查看当前数据库中所有的unlogged表

uber_geocoder=# select n.nspname as schema_name,c.relname as table_name from pg_catalog.pg_namespace n, pg_catalog.pg_class c where c.relnamespace=n.oid and n.nspname != ‘pg_toast‘ and c.relpersistence = ‘u‘;
       schema_name        |        table_name         
--------------------------+---------------------------
 edbstore                 | emp
 uber_geocoder_tw_15q3_v2 | twn_addr_compact_unloggod
(2 rows)

如果需要批量将unlogged表修改为正常的表，则执行如下

uber_geocoder=# select ‘ALTER TABLE‘||‘ ‘||concat(n.nspname,‘.‘ ,c.relname)||‘ ‘||‘SET LOGGED ;‘ AS convert_logged_sql from pg_catalog.pg_namespace n, pg_catalog.pg_class c where c.relnamespace=n.oid and n.nspname != ‘pg_toast‘ and c.relpersistence = ‘u‘;
                             convert_logged_sql                              
-----------------------------------------------------------------------------
 ALTER TABLE edbstore.emp SET LOGGED ;
 ALTER TABLE uber_geocoder_tw_15q3_v2.twn_addr_compact_unloggod SET LOGGED ;
(2 rows)

 

PostgreSQL unlogged表

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