Arthur Gay

This plugin allows user to know if his username is available while typing. No further need to hit the “submit” button to check username availability. Each times the user types a character in the username textfield, an ajax request is send to a php script which check username availability.
<h3>Credits</h3>
Images by Pixel Mixer – www.pixel-mixer.com

Live username availability checking

A plugin for live username availability checking.

Automattic

Matt Mullenweg

Peter Westwood

Michael Adams (mdawaffe)

Ryan Boren

Andy Skelton

Barry

vnsavage

WordPress VIP

HyperDB is a very advanced database class that replaces a few of the WordPress built-in database functions. The main differences are: 
* HyperDB can be connect to an arbitrary number of database servers, 
* HyperDB inspects each query to determine the appropriate database.
It supports:
<ul>
<li>Read and write servers (replication)</li>
<li>Configurable priority for reading and writing</li>
<li>Local and remote datacenters</li>
<li>Private and public networks</li>
<li>Different tables on different databases/hosts</li>
<li>Smart post-write master reads</li>
<li>Failover for downed host</li>
<li>Advanced statistics for profiling</li>
<li>WordPress Multisite</li>
</ul>
It is based on the code currently used in production on WordPress.com with many MySQL servers spanning multiple datacenters.

HyperDB

HyperDB is a amazing feature.


	You want to make two websites share a (user) table? OK!
	You want to make a website use two databases so we can create a development workflow to "deploy" content in the same time we persist production data? OK!
	And so on...


Of course is unnecessary to talk about how it can help in scaling... Just perfect.


It's just amazing!

This plugin works very well with AWS RDS and read replica.

Works very well with RDS and read Replica

Maybe this plugin is not so popular because many WordPress users are just not technical users, but I truly glad the plugin is here, and hopefully the WordPress team still always have a time to maintenance this :)

Kudos! 

A hidden gem

HyperDB is an advanced database class that supports replication, failover, load balancing, and partitioning.

Live username availability checking vs HyperDB