> col.ensureIndex({a:0}, {background: true});
 m31001| 2014-02-22T23:31:26.171-0800 [repl writer worker 1] build index on: server12844.server12844 properties: { v: 1, key: { _id: 1 }, name: "_id_", ns: "server12844.server12844" }
 m31001| 2014-02-22T23:31:26.171-0800 [repl writer worker 1] 	 added index to empty collection
 m31000| 2014-02-22T23:31:26.176-0800 [conn1] build index on: server12844.server12844 properties: { v: 1, key: { a: 0.0 }, name: "a_0", ns: "server12844.server12844", background: true }
 m31000| 2014-02-22T23:31:26.176-0800 [conn1] 	 building index in background
 m31000| 2014-02-22T23:31:26.180-0800 [conn1] build index done.  scanned 1000 total records. 0.004 secs
> assert.eq(2, col.getIndexes().length);
> 
> sleep(5000);
 m31001| 2014-02-22T23:31:26.218-0800 [repl writer worker 1] build index on: server12844.server12844 properties: { v: 1, key: { a: 0.0 }, name: "a_0", ns: "server12844.server12844", background: true }
 m31001| 2014-02-22T23:31:26.218-0800 [repl writer worker 1] index build failed. spec: { v: 1, key: { a: 0.0 }, name: "a_0", ns: "server12844.server12844", background: true } error: 13130 can't start bg index b/c in recursive lock (db.eval?)