Characterizing File Accesses in Android Applications and Caching Implications

In this paper, we explore Android applications’ file access characteristics, and find out that smartphone file accesses are different from traditional desktop applications in terms of the following aspects. 1) There exist a limited number of hot blocks, which are accessed consistently during the entire execution of an application. 2) Block accesses in Android are highly biased such that the top 20% blocks account for 80% of total accesses. 3) Hot blocks of the top 100 rankings are mostly involved in SQLite. 4) Unlike desktop applications, file accesses in Android applications are write-intensive. 5) In predicting future file accesses in Android applications, frequency is a better estimator than temporal locality. 6) The effect of traditional buffer cache is limited in Android as file I/O in Android has a lot of synchronous writes, which incurs immediate storage flushing. Based on these analyses, this paper presents the implication of buffer cache management in Android. Specifically, we add a small non-volatile write buffer and present how this write buffer can be managed efficiently. Experimental results show that the proposed scheme improves the storage write traffic by an average of 21.7% and a maximum of 48.1% compared to the conventional buffer cache system.