djspiewak

Quick Tips for Fast Code on the JVM

I was talking to a coworker recently about general techniques that almost always form the core of any effort to write very fast, down-to-the-metal hot path code on the JVM, and they pointed out that there really isn't a particularly good place to go for this information. It occurred to me that, really, I had more or less picked up all of it by word of mouth and experience, and there just aren't any good reference sources on the topic. So… here's my word of mouth.

This is by no means a comprehensive gist. It's also important to understand that the techniques that I outline in here are not 100% absolute either. Performance on the JVM is an incredibly complicated subject, and while there are rules that almost always hold true, the "almost" remains very salient. Also, for many or even most applications, there will be other techniques that I'm not mentioning which will have a greater impact. JMH, Java Flight Recorder, and a good profiler are your very best friend! Mea

LeCoupa

# Redis Cheatsheet
# All the commands you need to know


redis-server /path/redis.conf  # start redis with the related configuration file
redis-cli                      # opens a redis prompt


# Strings.

JonCole

Some of the Redis best practices content has moved

This content from this markdown file has moved a new, happier home where it can serve more people. Please check it out : https://docs.microsoft.com/azure/azure-cache-for-redis/cache-best-practices.

NOTE: Client specific guidance listed below is still valid and should still be considered. I will update this document once all content has been moved.

tristanfisher

Working with ansible-vault

---

I've been using a lot of Ansible lately and while almost everything has been great, finding a clean way to implement ansible-vault wasn't immediately apparent.

What I decided on was the following: put your secret information into a vars file, reference that vars file from your task, and encrypt the whole vars file using ansible-vault encrypt.

Let's use an example: You're writing an Ansible role and want to encrypt the spoiler for the movie Aliens.

wvuong

package com.willvuong.foodie.controller;

import com.willvuong.foodie.dao.PlaceRepository;
import com.willvuong.foodie.domain.Place;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

tmatilai

knife[:solo_path] = 'chef-solo' # relative to $HOME, but can be '/tmp/chef-solo' etc.

# knife-solo sets the KNIFE_SOLO variable when runnin on the work station
solo_path = ENV['KNIFE_SOLO'] ? knife[:solo_path] : File.expand_path(File.dirname(__FILE__))

data_bag_path             File.join(solo_path, 'data_bags')
encrypted_data_bag_secret File.join(solo_path, 'data_bag_key')
cookbook_path             [ File.join(solo_path, "site-cookbooks"),
                            File.join(solo_path, "cookbooks") ]
role_path                 File.join(solo_path, "roles")

jboner

Latency Comparison Numbers (~2012)
----------------------------------
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        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

puppybits

#!/bin/sh
# Examples:
# ./image64.sh myImage.png 
#   outputs: data:image/png;base64,xxxxx
# ./image64.sh myImage.png -img
#   outputs: <img src="data:image/png;base64,xxxxx">

filename=$(basename $1)
xtype=${filename##*.}
append=""

naaman

Hot Swapping With Maven, Jetty and IntelliJ

Based on Configuring Jetty, Maven, and Eclipse together with Hot Swap

I've always been a bit jealous when it comes to the Play! framework and the great dev mode they have for hot swapping classes at runtime. Jetty has a configuration setting, scanIntervalSeconds, that mimics this when working with a more traditional WAR, but does so by looking for changes to a file and restarting the server.

Fortunately, Jetty also provides the ability to rapidly test code with hot swapping. No more server restarts. The trick to getting hot swapping to work is to attach a remote debugger to your Jetty process. The following instructions outline how to do this in IntelliJ (tested with IDEA 10.5 CE).

Modify your jetty-maven-plugin to ignore the scan interval

1. Open your pom and locate the plugins section