[PostgreSQL] How to create read-only standby replica (follower)

This link and this link explain it really well and concise

Useful commands for observe running JVM process

$ jcmd

List running processes

$ jinfo 

Get details of a process

$ jps -lvm

List running processes with params

Clojure how to get JVM options from inside application

(.getInputArguments (java.lang.management.ManagementFactory/getRuntimeMXBean))

Credit: How to get vm arguments from inside of java application?

Clojure has lesser typing error problems than the others well-known dynamic typing languages

Give these snippets a try.

// JS
function foo () {
  bar(1)
}

# Ruby
def foo
  bar(1)
end

; Clojure
(defn foo [] 
  (bar 1))

As you can see from the images below, Clojure doesn't allow you to refer to an undeclared symbol. I believe this takes away quite a bit of typing error issues.

Config number of file descriptors on Linux

Check file descriptor limit for a process. Vary depending on owner of the process

$ cat /proc/{process-id}/limits

Check current number of file descriptors of a process

$ sudo ls /proc/{process-id}/fd | wc -l

Set file descriptors limit for a user at /etc/security/limits.conf

*    soft nofile 64000
*    hard nofile 64000
root soft nofile 64000
root hard nofile 64000

Check system file descriptor limit

$ cat /proc/sys/fs/file-max

Check current number of system file descriptors

$ cat /proc/sys/fs/file-nr 

Credits:

• Raising the Maximum Number of File Descriptors (Open Files) on Ubuntu 14.04 Trusty
• https://unix.stackexchange.com/a/104405

Increase video volume

$ ffmpeg -i input -vcodec copy -af "volume=20dB" output

Credit: How to increase volume in a video without re-encoding the video 

Convert .ts to .mp4

$ ffmpeg -i input.ts -acodec copy -vcodec copy out.mp4

Credit: http://stackoverflow.com/a/17916418/1032449