Oracle Database 11g shoots the moon
Oracle's enormous 11g release rumbles with an impressive array of performance and management aids, elegant application testing, standbys that earn their keep, and the promise of lower storage requirementsFollow @infoworld
You would expect from Advanced Compression that different tables and different data will behave differently, and this is just what my two tests showed. Two tables in the Oracle Test Kit not only compressed to a quarter of their original size, but reaped big gains in query performance and even improvements in write speeds. The TCP-C database tables compressed far less, ranging from 15 to 57 percent savings, and saw no benefit to query or write performance. In fact, performance took a hit. (See details of the two tests and tables of the results.)
Naturally, the results I got in my tests, and the results that Oracle gets in its tests, will not be the same as the results you get in your tests. Expect your compression results to differ from one table to another as well, sometimes dramatically. And be aware that making changes to the base-level table can change your compression ratio. If business or reporting requirements change (as they often do) and you have to order your table differently, you could lose a good deal of your compression. Worst-case scenario, you might suddenly find that you no longer have enough disk space.
Also note that Advanced Compression could impose a cost in system resources. When I set up the read tests for the TCP-C data, I ordered the tables to cluster all the like data together and then queried from that data specifically. I expected that clustering like data would greatly improve scan performance. But that's not what happened. So unless you test thoroughly and with your real production data, you may be surprised by the results.
Advanced Compression can be a huge asset for the smart DBA who manages it correctly and has the forethought to pull it off and maintain it well, but it adds a level of complexity to making changes that you have to be careful about. And even before you implement it, you'll need to do plenty of regression testing to ensure that your apps will work as before.
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