I don't have a good understanding of TokuDB, but I'm not sure the buffers are necessarily in memory. The problem the buffers solve is the cost of rebuilding the

I don't have a good understanding of TokuDB, but I'm not sure the buffers are necessarily in memory. The problem the buffers solve is the cost of rebuilding the index when you insert or delete data -- buffers allow you to delay the rebuild so as to batch many updates together. Even if the buffers were in memory, you'd still have the old (inconsistent) index on disk (presumably the index is marked inconsistent until the writes in the buffers are applied). You just need to rebuild it to match the new data.