Log shipping
Encyclopedia
Log shipping is the process of automating the backup of a database
and transaction log
files on a primary (production) database server, and then restoring them onto a standby server. This technique is supported by Microsoft SQL Server
and PostgreSQL
. Similar to replication
, the primary purpose of log shipping is to increase database availability by maintaining a backup server that can replace production server quickly.
Although the actual failover
mechanism in log shipping is manual, this implementation is often chosen due to its low cost in human and server resources, and ease of implementation. As comparison, SQL server clusters enable automatic failover, but at the expense of much higher storage and license costs. Compared to database replication, log shipping does not provide as much in terms of reporting capabilities, but backs up also system tables along with data tables, and locks standby server from users' modifications. A replicated server can be modified (e.g. view
s) and therefore is not suitable for failover purposes.
Database
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
and transaction log
Transaction log
In the field of databases in computer science, a transaction log is a history of actions executed by a database management system to guarantee ACID properties over crashes or hardware failures...
files on a primary (production) database server, and then restoring them onto a standby server. This technique is supported by Microsoft SQL Server
Microsoft SQL Server
Microsoft SQL Server is a relational database server, developed by Microsoft: It is a software product whose primary function is to store and retrieve data as requested by other software applications, be it those on the same computer or those running on another computer across a network...
and PostgreSQL
PostgreSQL
PostgreSQL, often simply Postgres, is an object-relational database management system available for many platforms including Linux, FreeBSD, Solaris, MS Windows and Mac OS X. It is released under the PostgreSQL License, which is an MIT-style license, and is thus free and open source software...
. Similar to replication
Replication (computer science)
Replication is the process of sharing information so as to ensure consistency between redundant resources, such as software or hardware components, to improve reliability, fault-tolerance, or accessibility. It could be data replication if the same data is stored on multiple storage devices, or...
, the primary purpose of log shipping is to increase database availability by maintaining a backup server that can replace production server quickly.
Although the actual failover
Failover
In computing, failover is automatic switching to a redundant or standby computer server, system, or network upon the failure or abnormal termination of the previously active application, server, system, or network...
mechanism in log shipping is manual, this implementation is often chosen due to its low cost in human and server resources, and ease of implementation. As comparison, SQL server clusters enable automatic failover, but at the expense of much higher storage and license costs. Compared to database replication, log shipping does not provide as much in terms of reporting capabilities, but backs up also system tables along with data tables, and locks standby server from users' modifications. A replicated server can be modified (e.g. view
View (database)
In database theory, a view consists of a stored query accessible as a virtual table in a relational database or a set of documents in a document-oriented database composed of the result set of a query or map and reduce functions...
s) and therefore is not suitable for failover purposes.
External links
- Log Shipping, MS SQL Server implementation
- Hot Standby, PostgreSQL implementation