Replication (computing)

Replication or replication ( " return " Latin replicare " repeat " ) refers to the multiple storage of the same data usually several different locations and synchronizing these data sources.

Basics

General serves replication in data processing to make data available in multiple locations. This is partly for data backup; other hand, for shortening the response times, especially for read data accesses.

The simplest form of data replication is to store a copy of a file (copy ), in expanded form copying and pasting ( copy & paste) modern operating systems.

Replication is the duplication of optical media in a press shop or using a torch.

Changing data accesses are expensive in general through replication. In the frequently encountered master / slave replication, a distinction between the "original " of the data (primary data ) and the dependent copies. In peer copies ( version control ) must be used in replication to Mergestrategien that enable the merging of the data sets (synchronization).

Sometimes it is important to know which actuality must have the replicas. Depending on the type of replication is located between the processing and creation of the primary data and their replication a certain period of time. This time, however, usually referred to as timelines, as latency.

Synchronous Replication

From synchronous replication is called when a change operation can not be concluded successfully on a data object, if it was performed on the replicas. In order to implement technically, a protocol to ensure atomicity is to be applied ( indivisibility ) of transactions, the commit protocol.

Strategies synchronous replication:

  • ROWA method
  • Voting procedures, for example, Weighted vote

Examples of synchronous replication are:

  • Hot Standby replication of SQL Server Microsoft Databases

Asynchronous replication

If there is a latency between the processing of the primary data and the replication, one speaks of asynchrony. The data is only available at the time of synchronous replication ( identical).

A simple variant of the asynchronous replication is the " File Transfer Replication ", the transfer of files via FTP or SSH.

The data of the replicas so represent only a snapshot of the primary data at a specific time dar. At the database level can so in short time intervals, the transaction log of the database to be transported from one server to another and read into the database.

Assuming an intact network latency then corresponds to the time interval in which the transaction is written.

Asynchronous replication strategies:

  • Merge Replication
  • Primary Copy
  • Snapshot replication
  • Standby replication

Advantages and disadvantages of replication

Benefits of replicas in distributed database systems:

  • Increased availability of data
  • Speeding up read access ( better response times, communication savings)
  • Better opportunities for load balancing and query optimization

Cons:

  • Increased memory footprint
  • Possible redundancy of records in case of possible networking

Applications

  • Data Warehousing
  • Balance of databases in the groupware
  • IT architecture
  • Parallel processing
  • IT security
  • Data synchronization
  • Replication ( data processing )
Merge (revision control) ACID Quorum (distributed computing)#Quorum-based techniques in distributed database systems Secure Shell Response time (technology) Integrated Authority File
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