Normally performance refers to the speed with which a system completes operations. This general consists of response time and throughput either of which could be more critical in a given situation. A system will have to meet certain performance criteria to be judged useful, and from this perspective has a subjective aspect.
Database systems often have issues with performance arising from queries with suboptimal plans that generate excessive I/O traffic. Where this happens it may be necessary to tune the system by modifying queries, adding indexes to the database or adjusting the memory allocation policies of the system. In more extreme cases the database structure may need to be modified or moved to an appropriate hardware platform.