Rajaneesh Rajaneeshs

HOWTO avoid 'too many connections'

Ask postgresql where is the configuration file

$ psql postgres
 psql (9.2.2)
   Type "help" for help.

tmux shortcuts & cheatsheet

start new:

tmux

start new with session name:

tmux new -s myname

tmux cheat sheet

(C-x means ctrl+x, M-x means alt+x)

Prefix key

The default prefix is C-b. If you (or your muscle memory) prefer C-a, you need to add this to ~/.tmux.conf:

remap prefix to Control + a

How Fast is Git?

The web is full of benchmarks showing the supernatural speed of Git even with very big repositories, but unfortunately they use the wrong variable. Size is not important, but the number of files in the repository really is!

Why is that? Well, that's because Git works in a very different way compared to Synergy. You don't have to checkout a file in order to edit it; Git will do that for you automatically. But at what price?

The price is that for every Git operation that requires to know which files changed (git status, git commmit, etc etc) an lstat() call will be executed for every single file

Wow! So how does that perform on a fairly large repository? Let's find out! For this example I will use an example project, which has 19384 files in 1326 folders.

Using strace and lsof to debug blocked processes

You can use strace on a specific pid to figure out what a specific process is doing, e.g.:

strace -fp <pid>

You might see something like:

select(9, [3 5 8], [], [], {0, 999999}) = 0 (Timeout)

	#!/usr/bin/php
	<?php
	/*
	* Convert JSON file to CSV and output it.
	*
	* JSON should be an array of objects, dictionaries with simple data structure
	* and the same keys in each object.
	* The order of keys it took from the first element.
	*
	* Example:

	-- show running queries (pre 9.2)
	SELECT procpid, age(clock_timestamp(), query_start), usename, current_query
	FROM pg_stat_activity
	WHERE current_query != '<IDLE>' AND current_query NOT ILIKE '%pg_stat_activity%'
	ORDER BY query_start desc;

	-- show running queries (9.2)
	SELECT pid, age(clock_timestamp(), query_start), usename, query
	FROM pg_stat_activity
	WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%'

	#!/usr/bin/env python

	import sys
	import boto
	import pprint

	del_flag = ''
	if len(sys.argv) > 1:
	del_flag = sys.argv[1]