Cost of ensuring safety in distributed database management systems

Abstract

Generally, applications employing database management systems (DBMS) require that the integrity of the data stored in the database be preserved during normal operation as well as after crash recovery. Preserving database integrity and availability needs extra safety measures in the form of consistency checks. Increased safety measures inflict adverse effect on performance by reducing throughput and increasing response time. This may not be agreeable for some critical applications and thus, a tradeoff is needed. This study evaluates the cost of extra consistency checks introduced in the data buffer cache in order to preserve the database integrity, in terms of performance loss. In addition, it evaluates the improvement in error coverage and fault tolerance, and occurrence of double failures causing long unavailability, with the help of fault injection. The evaluation is performed on a replicated DBMS, ClustRa. The results show that the checksum overhead in a DBMS inflicted with a very high TPC-B-like workload caused a reduction in throughput up to 5%. The error detection coverage improved from 62% to 92%. Fault injection experiments shows that corruption in database image went down from 13% to 0%. This indicates that the applications that require high safety, but can afford up to 5% performance loss can adopt checksum mechanisms.