There's a test for internal pages with a single child in the row-store search function:

/*
 * Fast-path internal pages with one child, a common case for
 * the root page in new trees.
 */
if (pindex->entries == 1) {
        descent = pindex->index[0];
        goto descend;
}

michael.cahill, you put this code in https://github.com/wiredtiger/wiredtiger/commit/875c10c72b6f5bdb53a8e14fc7e15f7491d6b412, do you remember where this made a difference?

It seems to me it's only useful until we split the root, and then it's wasted from that point on, was there a benchmark that triggered this?