LSMs need to be squashed once in a while, and it's less work to fold an LSM into a B-tree than it is to write the whole DB. I think LSMs work great as indexed

LSMs need to be squashed once in a while, and it's less work to fold an LSM into a B-tree than it is to write the whole DB. I think LSMs work great as indexed write-ahead logs. Like, the ZIL is essentially a write-ahead log, but it's not indexed. The ZIL should have been indexed so that if you crash you don't have to process the ZIL into the ZFS tree, instead you just run with it (this might also reduce the amount of RAM ZFS needs to track open transactions).