btree index pre-reading

[Martin Pool]

It's a good explanation and seems like a reasonable strategy to
pursue.  I don't have any suggestions without experimenting with it
myself.

At one point s/there/their/

> 2. Only expand within a layer. The problem is that with a 100:1 fan-out, but   only a 10:1 expansion policy, it is unlikely that we will happen to read the   next layer pages that we are interested in. Note that this doesn't hold true   when a layer has "recently split", so we may want to revisit this.

But since the size of the layers is not constant or predictable, it's
not obvious to me how you'll achieve this.

> I'll also note that small differences are probably not significant, as I'm doing this over the internet, with lots of variation.

You should try setting up netem as in the smart push analysis wiki
page or my recent mail.  It's very easy to set up and gives you more
reproducible results.

The numbers do look promising.

-- 
Martin <http://launchpad.net/~mbp/>