Deep Dive into AlwaysOn Availability Groups.

1. AlwaysOn Availability
Groups
Way Too Deep
Joey D’Antoni
SQL Saturday #164 Cleveland
18 August 2012

2. About Me
 Principal Architect SQL Server, Comcast Cable
 @jdanton
 Joedantoni.wordpress.com (Slides will be here and on SQL Sat site)
 jdanton1@yahoo.com

3. Agenda
 Overview of AlwaysOn
 Extended Events Briefly
 What Happens When?
 Turn on AlwaysOn
 We Build an Availability Group
 We add data to a Primary DB
 We backup the transaction log on the secondary
 We query the secondary DB

4. Warning
 You are going to see a few things that aren’t fully
documented
 We aren’t touching anything—just looking to see what’s
going on
 I’m telling you what I think is happening, I’m still trying to
get answers on some of it

5. Availability Groups

6. Extended Events
 Eventual Replacement for SQL Profiler Tracing
 612 Events in SQL 2012
 A significant portion of these deal with AlwaysOn (HADR)

7. What Happens When…
 We enable AlwaysOn

8. Enable AlwaysOn
 Demo

9. HADR_WSFC_CHANGE_NOTIFIER_STATUS

10. Creating an Availability Group
 Object in AD and DNS Gets Created (Listener)
 Database(s) get restored onto secondary
 Lots of Metadata gets created to Manage the Availability
Group

11. Building Availability Groups
 Demo

12. Moving Data
 Database Mirroring used a single thread per database to move data
 Always On is different—it uses a request pool that is shared between all
AlwaysOn Databases
 On the primary messages the active log scanner is the log pole.
 When a secondary is ready to receive log blocks a message is sent to the
primary to start the log scanning.
 This message is handled by a worker in the HadrThreadPool.

13. Moving Data

14. Moving Data
 Demo

15. Transaction Log Backup on Secondary
 One of the new features of 2012
 Allows us to flush the log on the primary database by backing up on the
secondary

16. Secondary Log Backup
 Demo

17. Querying Secondary Instance
 Another Big Feature of AlwaysOn Replicas
 Runs in Snapshot Isolation Transaction Level to Minimize Blocking Issues
 Creates Secondary Stats where missing—in TempDB

18. Stats on Secondary

19. Stats on Secondaries
 Demo

20. Summary
 AlwaysOn is pretty cool
 It’s clear a lot of work went into this
 It’s fairly complicated, but the good news is that it’s easy to work on

21. Questions

22. Contact
 @jdanton
 jdanton1@yahoo.com
 Joedantoni.wordpress.com