[anorwell]

I'm not sure I understand this. The claim is that "we dramatically improve the performance of insertions without hurting the IO cost of queries" by writing to the root's event log. However, it seems to me that this is only delaying the eventual write to the leaf node, not avoiding it. As more items are written, eventually the log will overflow and write to its children, and so on, until it is written to the leaf. This is what would happen in a regular B+ tree anyway, so what has been gained?

What am I missing?

[dgrnbrg]

It's not just the root's event log--it's all the event logs. The deferrals allow us to batch writes in an optimized way, and do so with a fully incremental algorithm. In the IO cost model, each "block" read or costs 1 IOP to perform, so we can reduce the IOP cost of writes by a factor of 100-1000x, but reads will still have the same # of nodes to fetch. The event logs augmenting the tree are an effective IO optimization on a B+ tree.

[anorwell]

Thanks, makes sense.