viksit

	

     
    summer = lambda acc, val: acc+val
    maxxer = lambda acc, val: max(acc, val)
    unioner = lambda acc, val: acc.union({val})
    def log(val):
        print 'value:', val
        return val
     

viksit

;; Non recursive function
(defn fib-nr [f]
  (fn [n]
    (if (< n 2) 1
        (+ ((f f) (- n 1))
           ((f f) (- n 2))))))
           
;; A U combinator that allows a generic application function 
(defn UM [myapply f]
  (defn g [v]

viksit

Latency Comparison Numbers
--------------------------
L1 cache reference                            0.5 ns
Branch mispredict                             5   ns
L2 cache reference                            7   ns             14x L1 cache
Mutex lock/unlock                            25   ns
Main memory reference                       100   ns             20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy              3,000   ns
Send 1K bytes over 1 Gbps network        10,000   ns    0.01 ms
Read 4K randomly from SSD*              150,000   ns    0.15 ms

viksit

Setting up Flume NG, listening to syslog over UDP, with an S3 Sink

My goal was to set up Flume on my web instances, and write all events into s3, so I could easily use other tools like Amazon Elastic Map Reduce, and Amazon Red Shift.

I didn't want to have to deal with log rotation myself, so I setup Flume to read from a syslog UDP source. In this case, Flume NG acts as a syslog server, so as long as Flume is running, my web application can simply write to it in syslog format on the specified port. Most languages have plugins for this.

At the time of this writing, I've been able to get Flume NG up and running on 3 ec2 instances, and all writing to the same bucket.

Install Flume NG on instances

viksit

/**
 * http://stackoverflow.com/questions/868482/simulating-mysqls-password-encryption-using-net-or-ms-sql
 * http://dev.mysql.com/doc/refman/5.0/en/encryption-functions.html#function_password
 **/
 
public static String MySQLPassword(String plainText) throws UnsupportedEncodingException {
    byte[] utf8 = plainText.getBytes("UTF-8");
    return "*" + DigestUtils.shaHex(DigestUtils.sha(utf8)).toUpperCase();
  }
  

viksit

'xxyxxyxyx'.replace(/[xy]/g, function(c) {
    var r = Math.random()*16|0, v = c == 'x' ? r : (r&0x3|0x8);
    return v.toString(16);
});

viksit

"""
Given a sequence of stock prices, what are the 2 values to buy and sell such that loss is maximized?
"""

prices = [[1,6,0,4,9,0,10],
          [1,2,3,4,5,6,7,8],
          [15,1,2,3,4,5,6,7,0],
          [7,3,9,5,2,1,4,14,16,17],
          [291, 592, 116, 480, 861, 438, 333, 541, 505, 272],
          [25, 679, 1, 493, 593, 579, 943, 258, 104, 997]]

viksit

(def file (File. "/tmp/outfile.dat"))

(def dos (-> file java.io.FileOutputStream. java.io.DataOutputStream.))

(defn write-seqs [#^java.io.DataOutputStream dos]
  (for [i (range 0 10)]
    (.writeInt dos i)))

(write-seqs dos)

viksit

(defn level-order [f tree]
  (loop [to-do [tree]]
    (if (empty? to-do)
      :done
      (do (dorun (map (comp f :value) to-do))
          (recur (mapcat (fn [{:keys [left right]}] (remove nil? [left right]))
                         to-do))))))

(level-order println
             {:value 1

viksit

(def bt {:left {:value 3}
         :value 5
         :right {:left {:value 2}
                 :value :foo
                 :right {:left {:value :bar}
                         :value :quux
                         :right {:value 10}}}})

(loop [bt bt
       q (clojure.lang.PersistentQueue/EMPTY)]