Anti-Freeze for Large and Complex Spreadsheets: Asynchronous Formula Computation

Spreadsheet systems enable users to store and analyze data in an intuitive and flexible interface. Yet the scale of data being analyzed often leads to spreadsheets hanging and freezing on small changes. We propose a new asynchronous formula computation framework: instead of freezing the interface we return control to users quickly to ensure interactivity, while computing the formulae in the background. To ensure consistency, we indicate formulae being computed in the background via visual cues on the spreadsheet. Our asynchronous computation framework introduces two novel challenges: (a) How do we identify dependencies for a given change in a bounded time? (b) How do we schedule computation to maximize the number of spreadsheet cells available to the user over time? We bound the dependency identification time by compressing the formula dependency graph lossily, a problem we show to be NP-Hard. A compressed dependency table enables us to quickly identify the spreadsheet cells that need recomputation and indicate them as such to users. Finding an optimal computation schedule to maximize cell availability is also NP-Hard, and even merely obtaining a schedule can be expensive-we propose an on-the-fly scheduling technique to address this. We have incorporated asynchronous computation in DataSpread, a scalable spreadsheet system targeted at operating on arbitrarily large datasets on a spreadsheet frontend.