No abstract

Many optimization schemes have been proposed to reduce the overhead of checkpointing. Incremental checkpointing based on memory page protection has been one of the successful schemes used to reduce the overhead and to improve the performance of checkpointing. In this paper, we propose two checkpointing schemes, called "block encoding'' and "combined block encoding", which further reduce the checkpointing overhead. The smallest unit of checkpoint data in OUT scheme is a block, which is smaller than a pagethis reduces the amount of checkpoint data required when compared with page-based incremental checkpointing.One drawback of the proposed schemes is the possibility of aliasing in encoded words. In this paper, however, we show that the aliasing probability is near zero when an &byte encoded word is used. The performance of the proposed schemes as analyzed and measured using experiments. First. we construct a n analytic model that predicts the checkpointing overhead. B y using this model, we can estimate the block size that produces the best performance for a given target program. Next, the proposed schemes are implemented on libckpt , a general-purpose checkpointing library for Unix based system which was developed at the University of Tennessee. According to OUT experimental results, the proposed schemes reduce the overhead by 11.7% in the best case and increase the overhead by 0.5% in the worst case in comparison with page-based incremental checkpointing. In most cases, the combined block encoding scheme shows an improvement over both block encoding and page-based incremental checkpointing.

Fault-tolerant computer systems are being used increasingly in such applications as e-commerce, banking, and stock trading, where privacy and integrity of data are as important as the uninterrupted operation of the service provided. While much attention has been paid to the protection of data explicitly communicated over the Internet, there are also other sources of information leakage that must be addressed. This paper addresses one such source of information leakage caused by checkpointing, which is a common method used to provide continued operation in the presence of faults.Checkpointing requires communication of memory state information, which may contain sensitive data, over the network to a reliable backing store. Although the method of encrypting all of this memory state information can protect the data, such a simplistic method is an overkill that can result in a significant slowdown of the target application. This paper examines ways to combine the operations required to perform incremental checkpointing with those required to encrypt this memory state data. Analysis and experimentation on an actual system are used to show that the proposed secure checkpointing schemes are feasible and require a relatively low level of overhead.

Recently proposed probabilistic checkpointing has one drawback, namely aliasing. When analyzed, 64-bit signatures show negligible possibility of aliasing. But in practice, the shift-XOR signature generation function used with probabilistic checkpointing shows a high aliasing rate, which limits the practicality of probabilistic checkpointing. In this paper, two enhancements are considered to make probabilistic checkpointing more reliable. One is the signature generation function and the other is the recovery scheme. In the signature generation function part, we propose two signature generation functions: HALF for small block sizes (less than or equal to 256 bytes) and C-HALF(CRC combined HALF) for large block sizes (larger than 256 bytes), which have an aliasing probability similar to analytic results and small overhead. In the recovery scheme part, we propose a recovery scheme which ensures the safety of probabilistic checkpointing. To examine the correctness of previous checkpoints at recovery time, the proposed recovery scheme uses a spare node. We analyze the recovery scheme using a mathematical model. Also an optimal checkpoint interval is derived using the model.