graph1zzlle

/**
  * https://github.com/binance-exchange/binance-official-api-docs/blob/master/web-socket-streams.md#how-to-manage-a-local-order-book-correctly
  * @param asset
  * @param getSnaptshot
  */
class OrderBookFlow(
    asset: Asset,
    getSnaptshot: Asset => Future[OrderBook]
) extends GraphStage[FlowShape[OrderBookUpdateEvent, OrderBook]] {

graph1zzlle

(defn compute-percentile
  ; This function compute a percentile over a sequence of numbers.
  [percentile coll]
  {:pre [(number? percentile) (> percentile 0) (< percentile 1) (not (empty? coll))]}
  (let [sorted (sort coll)
        length (count coll)
        index (* percentile length)]
    (if (== (int index) index)
      (let [first (nth sorted (- index 1))
            second (nth sorted index)]

graph1zzlle

;; SCENARIO: Be able to detect high heap pressure on service. 
;; -> If during the last x minutes, "heap.usage" values are > 0.70, then alert... 
;; Riemann API http://riemann.io/api.html

(defn slack-this-shit [message]
  (slack slack-alert-channel {:username "Not so friendly Riemann bot",
                             :formatter (fn [ev] {:text (str "*"(:service ev)"*" " is in *" (:state ev) "* state on hosts: *" (:host ev) "*. " message),
                                                  :icon ":x:"})}))

(def tracking-jvm-pressure-stream

graph1zzlle

Yesterday I upgraded our running elasticsearch cluster on a site which serves a few million search requests a day, with zero downtime. I've been asked to describe the process, hence this blogpost.

To make it more complicated, the cluster was running elasticsearch version 0.17.8 (released 6 Oct 2011) and I upgraded it to the latest 0.19.10. There have been 21 releases between those two versions, with a lot of functional changes, so I needed to be ready to roll back if necessary.

Our setup:

• elasticsearch

We run elasticsearch on two biggish boxes: 16 cores plus 32GB of RAM. All indices have 1 replica, so all data is stored on both boxes (about 45GB of data). The primary data for our main indices is also stored in our database. We have a few other indices whose data is stored only in elasticsearch, but are updated once daily only. Finally, we store our sessions in elasticsearch, but active sessions are cached in memcached.

graph1zzlle

;; Fix for the compiling problem on IntelliJ with La-Clojure:
;; Settings -> Compiler -> Clojure Compiler -> Copy Clojure source files to output...


(filter odd? [1 2 3 4 5 6])        ;; => 1 3 5
(first(filter odd? [1 2 3 4 5 6])) ;; => 1

(first '(1 2 3))                   ;; => 1
(first [1 2 3])                    ;; => 1
;(first (1 2 3))                   ;; => error ! because (1 2 3) is not interpreted as a list here

graph1zzlle

var thing = require('./thing.js');

/*****************************************************
 * CLASS DEFINITION
 ****************************************************/
function someManager() {
  
    this.thing = thing;
    this.otherThing = {};
};

graph1zzlle

Notes are actually on:

• callbacks
• objects
• prototype
• namespaces

graph1zzlle

As I want to kickstart javascript development very fast, I have found those roadmaps. They are freshly updated with latest stuff. I will complete my learning with SPA course from [http://singlepageappbook.com/][spa-url]:

1. http://javascriptissexy.com/how-to-learn-javascript-properly/

2. http://javascriptissexy.com/learn-intermediate-and-advanced-javascript/

3. // learn angular.js

4. http://javascriptissexy.com/learn-node-js-completely-and-with-confidence/