Oracle Multitenant Option is the one of the most exciting enhancements in the Oracle Database probably in the last decade. It's definitely my favorite feature since 12c due to the elegant way it simplifies database consolidation projects. For more information about Oracle Multitenant, check out my blog post: http://oracledbpro.blogspot.com/2016/10/otn-appreciation-day-oracle-multitenant.html
Oracle Multitenant 18c New Features - The Good
There are several nice Oracle Multitenant related enhancements in 18c which I believe worth mentioning in this blog post
- Refreshable PDB Switchover - In Oracle 12c Release 2, Oracle introduced the refreshable PDB feature which allows to refresh a cloned PDB either on-demand or on a scheduled frequency. You can think of it as a poor-man standby because it's not designed for failover but more for having a cloned environment updated without having to completely clone the entire database every time (which may take a while). This could be very helpful for reporting/query offloading. Oracle 18c took this feature one step ahead and now enables to perform a switchover between the 2 PDBs which could be useful for load balancing purposes (planned switchover) as well as high availability when a PDB fails. Please note that this feature is not a replacement for data guard and should not be used as a DR solution for mission critical applications
- Enhanced Data Guard Integration - In Oracle 12c, when Multitenant was configured in a data guard environment there were some challenges. Oracle 12cR2 introduced the hot clone feature which was a huge improvement as it allowed cloning a PDB with no downtime; however, when hot cloning a PDB, it was not performed on standby - in other words, it wasn't replicated also in the standby CDB (similar to specifying standbys=none). In Oracle 18c this challenge has been addressed by additional steps which required to be done. For more details, see: https://www.oracle.com/technetwork/database/multitenant/learn-more/multitenantwp18c-4396158.pdf
- Snapshot Carousel - Stores historical point in time copies of pluggable databases (up to 8 in the current 18c release). This is useful for historical debugging of data related issues as well as for point-in-time recovery of a PDB (similar to flashback database feature, but without enabling flashback database)
- CDB Fleet Management - CDB allows to manage many PDBs as one (up to 4096 PDBs in Oracle Exadata and Oracle cloud, and 252 for every other deployment) - which is the main benefit of database consolidation. Now, in Oracle 18c using this new feature it's possible to manage many CDBs as one. I personally think this could be useful for the very large enterprise companies who manage huge amount of databases)
Oracle Multitenant 18c New Features - The Bad
According to Oracle documentation, all the above features (except the enhanced data guard integration), are only available either on Oracle Exadata or Oracle cloud. Most of the Oracle customers probably don't use neither Oracle Exadata nor Oracle cloud which makes these features unavailable for most Oracle customers. I hope this will be changed in the future.
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