Consider having lsm-tree as default storage engine for wiredtiger

[dyu]

Or maybe as another variant included in the benchmark?

-static int indexing_type = 0;
+static int indexing_type = 1;

Also, rocksdb has a prefix-db variant (better random-read perf) that could be included.

[chiyoung]

Thanks for a good suggestion. We will add the LSM-tree option for WiredTiger.