DejaView: a personal virtual computer recorder

As users interact with the world and their peers through their computers, it is becoming important to archive and later search the information that they have viewed. We present DejaView, a personal virtual computer recorder that provides a complete record of a desktop computing experience that a user can playback, browse, search, and revive seamlessly. DejaView records visual output, checkpoints corresponding application and file system state, and captures displayed text with contextual information to index the record. A user can then browse and search the record for any visual information that has been displayed on the desktop, and revive and interact with the desktop computing state corresponding to any point in the record. DejaView combines display, operating system, and file system virtualization to provide its functionality transparently without any modifications to applications, window systems, or operating system kernels. We have implemented DejaView and evaluated its performance on real-world desktop applications. Our results demonstrate that DejaView can provide continuous low-overhead recording without any user noticeable performance degradation, and allows browsing, search and playback of records fast enough for interactive use

Furaldehyde substrate specificity and kinetics of Saccharomyces cerevisiae alcohol dehydrogenase 1 variants

Background A previously discovered mutant of Saccharomyces cerevisiae alcohol dehydrogenase 1 (Adh1p) was shown to enable a unique NADH-dependent reduction of 5-hydroxymethylfurfural (HMF), a well-known inhibitor of yeast fermentation. In the present study, site-directed mutagenesis of both native and mutated ADH1 genes was performed in order to identify the key amino acids involved in this substrate shift, resulting in Adh1p-variants with different substrate specificities. Results In vitro activities of the Adh1p-variants using two furaldehydes, HMF and furfural, revealed that HMF reduction ability could be acquired after a single amino acid substitution (Y295C). The highest activity, however, was reached with the double mutation S110P Y295C. Kinetic characterization with both aldehydes and the in vivo primary substrate acetaldehyde also enabled to correlate the alterations in substrate affinity with the different amino acid substitutions. Conclusions We demonstrated the key role of Y295C mutation in HMF reduction by Adh1p. We generated and kinetically characterized a group of protein variants using two furaldehyde compounds of industrial relevance. Also, we showed that there is a threshold after which higher in vitro HMF reduction activities do not correlate any more with faster in vivo rates of HMF conversion, indicating other cell limitations in the conversion of HMF

Speculative Memory Checkpointing

High-frequency memory checkpointing is an important tech-nique in several application domains, such as automatic error recovery (where frequent checkpoints allow the sys-tem to transparently mask failures) and application debug-ging (where frequent checkpoints enable fast and accurate time-traveling support). Unfortunately, existing (typically incremental) checkpointing frameworks incur substantial per-formance overhead in high-frequency memory checkpointing applications, thus discouraging their adoption in practice. This paper presents Speculative Memory Checkpointing (SMC), a new low-overhead technique for high-frequency memory checkpointing. Our motivating analysis identifies key bottlenecks in existing frameworks and demonstrates that the performance of traditional incremental checkpoint-ing strategies in high-frequency checkpointing scenarios is not optimal. To fill the gap, SMC relies on working set estimation algorithms to eagerly checkpoint the memory pages that belong to the writable working set of the run-ning program and only lazily checkpoint the memory pages that do not. Our experimental results demonstrate that SMC is effective in reducing the performance overhead of prior solutions, is robust to variations in the workload, and incurs modest memory overhead compared to traditional incremental checkpointing