Redundancy and Replication PDF

107 Redundancy and Replication [ Redundancy ]()...is the duplication of critical components or functions of a system with the intention of increasing * * ***...

107 Redundancy and Replication [ Redundancy ]()...is the duplication of critical components or functions of a system with the intention of increasing * * *** *** the reliability of the system, usually in the form of a backup or fail-safe, or to improve actual system *** *** *** *** *** *** * performance. * * For example, if there is only one copy of a file stored on a single server, then losing that server * *** *** * * * * * means losing the file. Since losing data is seldom a good thing, we can create duplicate or * * redundant copies of the file to solve this problem. * *** Redundancy plays a key role in removing the single points of failure in the system and provides *** * backups if needed in a crisis. ** ** * * For example, if we have two instances of a service running in production and one fails, the * *** *** * * system can failover to the other one. * * Database replication...is the process of copying and synchronizing data from one database to one or more additional * * *** *** databases. This is commonly used in distributed systems where multiple copies of the same data are * * required to ensure data availability, * * * fault tolerance, * and scalability. * * Replication is widely used in many database management systems (DBMS), usually with a primary- * * *** replica relationship between the original and the copies. *** * ** ** ** ** * 1. The primary server gets all the updates, which then ripple through to the replica servers. * * * * * * * * 2. Each replica outputs a message stating that it has received the update successfully, thus allowing * * * * the sending of subsequent updates. * *  * Here are the top three typical database replication strategies: * **~* Synchronous replication * ~**...is a type of database replication where changes made to the primary database are immediately * * *** replicated to the replica databases before the write operation is considered complete. In other *** *** *** * words, the primary database waits for the replica databases to confirm that they have received * == *** *** and processed the changes before the write operation is acknowledged. == == * In synchronous replication, there is a strong consistency between the primary and replica * *** *** * databases, as all changes made to the primary database are immediately reflected in the replica * * databases. This ensures that the data is consistent across all databases and reduces the risk of data *== == * * * * * loss or inconsistency. * == ~* Asynchronous replication * ~...is a type of database replication where changes made to the primary database are not immediately * ** ** replicated to the replica databases. Instead, the changes are queued and replicated to the replicas * * * *** at a later time. *** == * In asynchronous replication, there is a delay between the write operation on the primary database * *** *** *** ** * and the update on the replica databases. This delay can result in temporary inconsistencies * * *** *** between the primary and replica databases, as the data on the replica databases may not *** immediately reflect the changes made to the primary database. *** == * However, asynchronous replication can also have performance benefits, * * * == as write operations can be completed quickly without waiting for confirmation from the *** *** replica databases. == == * In addition, if one or more replica databases are unavailable, the write operation can still be * * * * completed on the primary database, ensuring that the system remains available. * * *== ~* Semi-synchronous replication * ~...is a type of database replication that combines elements of both synchronous and asynchronous *** ** replication. In semi-synchronous replication, changes made to the primary database are * *** immediately replicated to at least one replica database, while other replicas may be updated *** *** asynchronously. *** In semi-synchronous replication, the write operation on the primary is not considered complete until * * * * * ** ** ** at least one replica database has confirmed that it has received and processed the changes. This ** * == * ensures that there is some level of strong consistency between the primary and replica databases, * *** *** * while also providing improved performance compared to fully synchronous replication. * ==