On 11/04/2011 11:21 AM, Phillip Susi wrote: > Given how a transaction is committed, why is there a tree-log? When > modifying the tree, either the super block is still pointing to the > old tree root, or the new generation has been fully committed, so how > can there ever be an intermediate state that needs a log to recover? tree-log is for improving the preformance of fsync and and O_SYNCs. Btrfs has an expensive "commit transaction", if we commit a transaction every time we fsync, the performance is not that good. Instead of this, we introduce a write-ahead log to make our fsync faster. So if you do fsync for your data, it means your data is safely in the log tree, then if a crash takes place, the data can be recovered from log. More details are in tree-log.c. thanks, liubo -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
