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Dbvisit Product Comparison: Standby or Replicate?
- Oracle Business Continuity solution
- Performs physical database duplication - the secondary is exactly the same as the primary, both in terms of data and structure
- Enables DR functions such as Graceful Switchover and Failover, along with creation of the standby database
- Allows use of standby database in Read-Only mode (when recovery mode is turned off)
- Replicates selected Oracle database environments for the purposes of Data Migration, Reporting, Real-time Business Decisions, ETL extract solution
- Performs logical database replication - the target can be a subset of data, and the structure can be different
- Enables replication between different Oracle versions and operating systems, and the target database can be non Oracle (SQL Server and MySQL).
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Key distinctions between physical and logical replication:
- Physical replication is a binary copy of the primary or source database. Changes are applied at the lowest level available within the DBMS, ensuring that the target or standby database is an exact replica of the primary database, including all internal database indexes, pointers and tables.
- A logical replicated database is an independent database that is kept in sync by a replication mechanism that applies updates at the logical level (e.g. via SQL statements). This means that while the data within a logical target database may be the same as that in the primary or source database, the internal database-level structures will be different. This may have implications for some applications, and for the usage of the logical replicated database in the event of a failure. This is important as the database must be viewed not only as a repository of application data, but also a container with its own management and administrative data. For example, if a password is changed in the source database it is not updated in the target, then when it comes to failover the system will not work because of an old password. It also means that, although internal linkages that support referential integrity may be in place in the standby database, these may be physically different than at the primary site, and as a result, may have an impact on the application (e.g. different automatically created foreign key values).
- Physical replication is all or nothing. Either 100% of the database is replicated or nothing at all.
- With logical replication it is possible to only replicate a subset of the database in the database (100% replication is also possible).
- Physical replication is analogous with using a tool such as rsync to synchronize Word document, with rsync replicating the file at the binary file level.
- A logical standby database is analogous with manually updating a Word document by scanning for changes in the source file and copying them to the right location within the standby file.
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