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Presentation
Software Fault-Tolerance with Off-the-Shelf SQL Servers |
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With off-the-shelf software, software fault tolerance is almost the only means available for assuring better dependability than the off-the-shelf software offers, without the much higher costs of bespoke development or extra V&V. We report our experience with an experimental setup we have developed with off-the-shelf SQL database servers. First, we describe the use of a protective wrapper to mask the effects of a bug in one of the servers, without depending on an adequate fix from the vendors. We then discuss how to combine the diverse off-the-shelf servers into a diverse modular redundant configuration (N-version software or N-self-checking software). A wrapper guarantees the consistency between the diverse replicas of the database, serving multiple clients, by restricting the concurrency between the client transactions. We thus show that diverse modular redundancy with protective wrapping is a viable way of achieving fault-tolerance with even complex off-the-shelf components, like database servers. | ||||||||||||||||||||||
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