exF2FS: Transaction Support in Log-Structured Filesystem

In this work, we develop a transactional log-structured filesystem. The proposed filesystem consists of three key technical ingredients; Membership-Oriented Transaction, Stealing support in the transaction, and Shadow Garbage Collection. Membership-Oriented Transaction allows the transaction to span multiple files where the application can explicitly specify the files associated with a transaction. Stealing enabled transaction allows the application to execute the transaction with a small amount of memory and to encapsulate a large number of updates, e.g., hundreds of files with tens of GByte size in total, with a single transaction. Shadow Garbage Collection allows the log-structured filesystem to perform the garbage collection without affecting the failure-atomicity of the ongoing transaction. We call a newly proposed filesystem as exF2FS, a variant of F2FS. A transaction support in exF2FS is carefully trimmed to meet the critical needs of the application while minimizing the code complexity and avoiding any performance side effect. With transaction support, exF2FS greatly simplifies the implementation of transaction that spans multiple files, e.g.~multi-file transaction in SQLite, compaction in RocksDB, and software installation. With exF2FS transaction, SQLite multi-file transaction throughput increases by 24x against the multi-file transaction of stock SQLite. RocksDB throughput increases by 87% when it implements the compaction as a filesystem transaction. exF2FS is fully compatible with F2FS.