skreebydba

"Any sufficiently advanced technology is indistinguishable from magic." -Arthur C. Clarke

In this morning's keynote session at PASS Summit 2018, public preview of a new feature in Azure SQL Database and SQL Server 2019 called Accelerated Database Recovery (ADR) was announced.  This changes the way that SQL Server handles recovery of a SQL Server instance on start up.

Historically, instance recovery runs three phases.  Phase one - Analysis - scans the transaction log for each database looking for two types of transactions:

• Transactions that committed prior to instance shutdown but did not harden the associated data pages to the data file on disk
• Transaction that started prior to instance shutdown without committed

Phase two - Redo - rolls forward the transactions identified in the first bullet point.

Phase three -Undo - rolls back uncommitted transactions identified in the second bullet point.

If long-running transactions need to be rolled forward or back, database recovery can take a long time.  In my experience, six hours is the longest recovery I have seen, but I know people who have seen much longer.

This leads me to Accelerated Database Recovery and the Arthur C. Clarke quote above.  ADR is not magic, and you can learn more about it at the link above, but it is a huge leap in SQL Server behavior and will pay huge dividends in database and instance availability.

I will continue my series on Managed Instance after returning from Summit, and will post more information about ADR once I get a chance to play with it.