Are you ready to unlock the power of Microsoft SQL Server 2014? In this blog entry I will examine my 3 favorite new features that show how SQL Server 2014 provides high-performance OLTP, optimization of business analytics and migration of data to the cloud.
Three underlying themes categorize the SQL Server 2014 release: Mission Critical Performance, Faster Insights From Any Data and Platform for Hybrid Cloud. I have chosen one selected new feature under each theme to give a feel for the capabilities of the new release.
Selected Feature: In-Memory OLTP
It has always been true that increasing Physical Memory improves the performance of a database server. Logical I/O operations straight from physical memory are much faster than the physical I/O equivalent from storage. In SQL Server 2014, Microsoft is introducing the In-Memory OLTP database engine which essentially performs the entire I/O operation set against selected tables straight from memory. Included in the new architecture is a lock-less concurrency model plus the support for natively compiled stored procedures resulting in recorded performance gains up to 20x on the same hardware. The In-Memory OLTP option is an Enterprise-level feature and, as the name suggests, is designed specifically for typical OLTP traffic balancing read/write operations on the data with concurrent access. It has to be enabled at the database level before proceeding to create Memory-optimized tables.
To enable a database to host Memory-optimized tables, a special FILEGROUP needs to be added first to the database which CONTAINS MEMORY_OPTIMIZED_DATA. This Filegroup creates a folder to contain the memory-optimized data before it is loaded into memory.
There are various restrictions that apply to the new In-Memory OLTP feature. For instance, FOREIGN KEY constraints, DEFAULT constraints, CHECK constraints, IDENTITY columns and Triggers are not allowed on Memory-optimized Tables. However, if any of the restricted functionality is required, it can usually be coded using natively compiled Stored Procedure code. To assist with the migration to Memory-optimized tables, SQL Server Management Studio has a Table Memory Optimization Advisor which will give expert advice on the restrictions and how to work-around them, if necessary.
For instance, a table that currently has DEFAULT constraints will need to have those removed if it is to be migrated to a Memory-optimized Table. If a Stored Procedure for inserts is created, equivalent processing can be coded and the performance advantage of In-Memory OLTP can be realized. Example code is shown if you click a “Show me how” hyperlink in the Advisor.
When looking at a valid CREATE TABLE statement for a Memory-optimized table, the MEMORY_OPTIMIZED = ON clause is a requirement. The DURABILITY = SCHEMA AND DATA clause will make sure the updates are written to the Transaction Log on disk even though the access and updates to the table are made fully in memory. With the absence of locks in the new architecture, this will enable great performance gains while protecting the transactions in case of failure. In rare circumstances where the latest transactions do not need to be recoverable, DURABILITY = SCHEMA_ONLY can be used but is not recommended for obvious reasons.
I downloaded a sample from Microsoft’s www.codeplex.com code-sharing web site to test In-Memory OLTP versus the classic on-disk model with SQL Server 2014. I setup a Windows Azure VM (see later in this blog) using Windows Server 2012 R2 and SQL Server 2014 CTP2 with a predefined image from the Windows Azure Image Gallery. The sample tests out heavy duty updates using a stress testing tool OSTRESS with both memory-optimized and disk-based tables. In my limited tests, the memory-optimized tables handled 1000 transactions repeated across 100 threads yielding a 6x improvement over the equivalent disk-based tables. The disk I/O was dramatically reduced but not completely removed as the transaction log still needed to be updated on disk for durability reasons. This test was made against the upgraded AdventureWorks2012 database as a proof of concept.
Codeplex sample available at: http://msftdbprodsamples.codeplex.com/releases/view/114491
I ran my tests with a lightweight VM using a dual-core CPU and 3.5GB of memory as a simple proof-of-concept. The author of the sample used a machine with 24 logical cores and separate SSD drives for data and log files to yield an impressive 50x improvement.
Selected Feature: Clustered Columnstore Index
In SQL Server 2012, Microsoft introduced the Non-Clustered Columnstore index which was perfectly designed for large Fact tables in a Data Warehouse and provided an order of magnitude performance gain based on massive column compression and optimized “star” queries typical in such a database. The major restriction of this type of index was that a table could operate only as a read-only table while the Columnstore index was in place. Of course, in a typical Data Warehouse the data is read-only during the day while changes are applied at off-peak times. Indexes are typically dropped and recreated before and after the incremental updates so this was not a major restriction for most installations. Workarounds included the concept of a separate “Delta” table of the same structure where changes could be made and consolidated with the main table at a later time. A similar solution used Partition switching to achieve the same result. Now in SQL Server 2014 you can create a Clustered Columnstore Index which is now updateable.
In testing this out, the Clustered Columnstore Index (CCI) did yield similar performance gains (over 10x) to its Non-Clustered cousin and did accept updates as designed. However, as with all features, there is a trade-off of some sort. In this case, the CCI must be the only index on the table and it does not support Primary or Foreign Key constraints. So, in order to test this out on an existing table, I had to remove all PK and FK constraints and any other indexes first. As with all Clustered Indexes, all columns are contained in the CCI. Internally, the CCI actually manages a Delta table of its own, merging the data into the table as appropriate. Again, the transaction log makes sure all updates are durable and recoverable. As in the In-Memory OLTP solution, validation provided by PK and FK constraints can be emulated through Stored Procedure code, if necessary. There are other restrictions which are fully documented in Books Online. The Clustered Columnstore Index is an Enterprise-level feature.
Selected Feature: New Cloud Migration Wizard
Cloud-based data provides increased flexibility and “elastic” scalability, ideal for rapidly growing organizations. There are still many unanswered security-based questions, but some databases may be appropriate to host in the cloud and synchronize with sensitive “on-premises” databases. This distributed approach to our data is a growing trend in the industry. Microsoft is at the forefront of this technology with its Windows Azure platform supporting SQL Azure for databases in the cloud. Windows Azure also supports the setting up of hosted Virtual Machines (VMs) which can support the full version of SQL Server, if needed. Once again, ease of use and lower costs are Microsoft’s value propositions. SQL Azure is now compatible with SQL Server 2014 and supports a new Cloud Migration Wizard.
Windows Azure and SQL Azure can be accessed directly using http://windowsazure.com . A 30-day free trial is available. After that, a monthly fee based on storage requirements and resources used, is charged. SQL Server databases can be created and populated using the web interface or using SQL Server Management Studio remotely, accessing the database server using the fully qualified DNS name (FQDN) provided by the Windows Azure platform. SSIS packages can also extract information from SQL Azure databases using the same FQDN. SQL Azure databases must use SQL Server authentication but can be accessed using any of the SSIS Tasks provided in the SSIS Toolbox. In this way, accessing data in the cloud is essentially the same as any other data source.
To migrate a database to the cloud, you can now use the new Cloud Migration Wizard which can be launched via SQL Server Management Studio 2014. You can choose to migrate an on-premises database to SQL Azure using the Task: “Deploy Database to Windows Azure SQL Database…” against your database. The wizard will report on any restrictions, such as every table must have a Clustered Index on SQL Azure, guiding you through the process of porting your database to the cloud.
If you prefer, you can setup a VM on Windows Azure to host the full version of SQL Server and use the Task: “Deploy Database to a Windows Azure VM…”. In this case, you are not restricted to the limitations of SQL Azure as you are effectively dealing with a normal instance of SQL Server that happens to be running on a Windows Azure VM using Cloud Services. I tested this out using a Windows Azure VM with Windows Server 2012 R2 running SQL Server 2014 CTP2 and successfully migrated a SQL Server 2014 database to a SQL Azure database. Then I connected to a SQL Azure database using SSMS 2014 and was able to deploy using the “Deploy Database to a Windows Azure VM…” option. Once again, impressive technology. Microsoft has successfully incorporated the cloud as an extension of their architecture rather than as a completely separate platform and as such is allowing customers to leverage existing technologies in what is being called the Hybrid Cloud.
Microsoft SQL Server 2014 has some great new features that will allow you to develop higher performing, more scalable next-generation applications using the hybrid cloud. The fact that the features are largely incremental in nature should reassure us that Microsoft is building on the established foundation of SQL Server 2008 and 2012. Using similar architecture and management tools, we should be able to smoothly upgrade our systems and skills based on the need for the new features and according to our own schedule.
Evaluation/Pre-Release copy available at http://www.microsoft.com/sql