Eddie Corrigall eddiecorrigall

AWS MySQL Debugging

This tutorial provides a means to enable slow query logs on MySQL.

Setting Up Parameters

Enable these on AWS RDS Parameter Groups.

slow_query_log: 1
long_query_time: 10

Python Socket Timeout

The Problem

It is well known that the standard python socket library has no default timeout (returns None).

[ec2-user@worker-node ~]$ python
>>> import socket
>>> socket.getdefaulttimeout()

Java

Polymorphism
- the ability of a variable, function, or object to take multiple forms
- to define one interface with multiple implementations
- compile-time: - using the same method name, but different signature
- run-time: - using a reference type to control which method is called
@Override Annodation
- Runtime polymorphism
Java determins which version super/sub class method to execute based on reference type of call

Unit test ideas

Deterministic VS Stocastic

Unit tests should always be deterministic / reproducable. It is hard to debug when tests might fail randomly.

Assign a seed to the RNG

Avoid conditional-statements

Unit tests should always follow the same execution path, and hit all asserts regardless of the global or local state. This ensures consistent behaviour and that there is no assumptions on whether conditional control flows have been accurately written.

Create fixtures from database not datasets

Blogs

highscalability.com
softwareengineeringdaily.com
news.ycombinator.com
martinfowler.com
jacquesmattheij.com
kitchensoap.com
scotch.io
techspot.zzzeek.org

Schedule

Day 1: Unix 101

Homebrew, Coreutils
Tools: ssh, nc, awk, grep, vim, cut, sort, tmux, less, tail, cut, ssh, htop, psql
Dotfiles: Configs: ~/.bashrc, ~/.pgpass, ~/.s3cfg, ~/.psqlrc, ~/ssh/config
What is
- source /data/virtualenv/default/bin/activate
- ssh deploy@::1
SSH tunnels
Reverse tunnel

Python Greenlets

Tutorial: http://mauveweb.co.uk/posts/2014/07/gevent-asynchronous-io-made-easy.html

Exception example: RuntimeError('application not registered on db instance and no application bound to current context',)

The app context is not transfered between threads / greenlets. Please see:

Software Engineering Tools

Efficient data transfer through zero copy

What is?

IO bound work

	#!/bin/bash

	# Usage: threaddump.sh <thread count threshold> <process name>

	# Example:
	# Run this command `nohup sh threaddump.sh 500 tomcat7 &` to capture a thread
	# dump when httpd connections exceeds 500.
	#
	# Logs are written to `nohump.out` in the users home directory.
	# Thread dump for tomcat will be written to `/var/log/tomcat7/catalina.out`.

	AWSTemplateFormatVersion: 2010-09-09
	Resources:
	VPC:
	Type: 'AWS::EC2::VPC'
	Properties:
	CidrBlock: 10.0.0.0/16
	InternetGateway:
	Type: 'AWS::EC2::InternetGateway'
	GatewayToInternet:
	Type: 'AWS::EC2::VPCGatewayAttachment'