synchronous_commit参数是WAL相关配置参数,用于指定当数据库提交事务时是否需要等待WAL日志写入硬盘后才向客户端返回成功,这个参数可选值多(on、off、local、remote_write、remote_apply 五种),参数值在单实例和主从复制场景下含义也不尽相同。恰好看pg大会ppt的时候发现有描述参数含义不错的图,结合之前看过的文章整理...
PostgreSQL were to crash, but notifthe standby suffers an operating-system-level crash, since the data has not necessarily reached stable storageonthe standby. Finally, the setting local causes commits to waitforlocal flush to disk, but notforreplication. Thisisnot usually desirable when synchrono...
local: local含义和on类似,表示提交事务时需要等待本地wal写入后才向客户端返回成功。 流复制环境 on: 表示流复制主库提交事务时,需等待备库接收主库发送的wal日志流并写入wal文件,之后才向客户端返回成功,简单的说on表示本地wal已落盘,备库的wal也已落盘,有两份持久化的wal,但备库此时还没有完成重做。 这个...
通过简单实验可以看出 fsync 由 on 设置为 off 时,性能有大概 15% 的提升。虽然性能提高了,但是风险加大了。 synchronous_commit 由 on 设置为 off 时,性能提升并不是特别明显。
关于同步参数synchronous_commit,下列说法正确的是: ()A.当设置为off时,则不能保证数据库的数据一致性B.如果存在备库,当设置为on时,则返回成功时,可以保证至少有2份持久化的WALC.当设置为remote_write时,主库会在备库完成WAL持久化之后才返回成功D.如果不存在备库
Uncomment only one, leave it on its own line: bug feature What happened: synchronous_commit设置为off时,持续给主机进行插入事务,事务间隔性阻塞1-2s What you expected to happen: synchronous_commit设置为off时,持续给主机进行插入事务,主机事务不阻塞 ...
设置为remote_apply时，主库会在所有备库完成WAL持久化之后就返回成功（）
To illustrate the impact of synchronous commit, take a simple INSERT command initiated on a database at the primary replica. That insert must be hardened on the transaction log file of the primary replicaandof the transaction log file on the secondary replica and then acknowledgement ...
Troubleshooting High HADR_SYNC_COMMIT wait type with AlwaysOn Availability Groupshttps://blogs.msdn.microsoft.com/sql_server_team/troubleshooting-high-hadr_sync_commit-wait-type-with-always-on-availability-groups/ SQL Server 2012 AlwaysOn – Part 12 – Performance Asp...
Hot on the heels of the last analysis showing the performance hit for a synchronous SQL Server AlwaysOn cluster, re-running the same tests show a distinct performance boost when asynchronous commits are used. In fact it’s nearly the same as standalone at that point, which ...