Live Activation

Live activation of replication followed. This approach ran smoothly at the beginning but, unfortunately, further problems gradually arose during continued production. These were minor bugs in Windows and a bigger problem in the context of CLOBs that were not replicated cleanly. These obstacles had to be worked through step by step.

Because the provision of the HA environment was not ensured at this time, a standby database was set up in parallel with Dbvisit Standby. This was not a problem regarding either performance aspects or a license. Dbvisit provided the Standby license free of charge for as long as the problems with replication were not solved.

All in all, a number of checks and procedures need to be established for the regular operation and a possible switchover, as well as for the failover, to ensure smooth replication and a secure HA environment. Difficulties, complexities, and limitations resulted in an unexpected solution at the end of this project. Together with Dbvisit Standby, a double strategy, so to speak, was implemented that benefitted from the advantage of both solutions: All restrictions regarding non-replicated DDLs, SYS and SYSTEM schemes, and data types using Dbvisit Standby were bypassed, which allowed losses of actual production data to remain as low as possible using replication.

Another advantage is seen in the ease of handling Dbvisit Standby during a switchover. The replication is simply suspended. When a failover occurs (i.e., a total failure of the primary server), the standby database can be activated and, in case of doubt, lost data that has reached the other side via replication, can be imported using a DB Compare.

Conclusions

Is logical replication therefore suitable for implementing a high-availability environment? Sadly, the unsatisfactory answer is: It depends. A standby database provides the advantage of close integration in the database architecture. However, it is static, but very robust, when it is installed correctly.

In this case, several problems and all the options in Oracle Database Standard Edition bring the logical replication to its limits. The more complex the database structure, the less advisable it becomes to rely solely on logical replication. With additional goals, such as a user-friendly switchover, the IT manager must opt for the simpler standby solution with time offset or accept additional costs in the Enterprise Edition and Data Guard (or other products).