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SQL Server for Linux gets closer -- Windows database adds HA traits

SQL Server for Linux has gained added features on its way to general availability as part of the almost-ready SQL Server 2017. Meanwhile, its Windows-based brother is upping its high availability quotient.

The formal release of SQL Server for Linux moved closer to reality last week, as Microsoft rolled out SQL Server 2017 Release Candidate 1. The release includes elements that fill out the SQL Server port to Linux, an operating system that was once persona non grata within the confines of Microsoft's Redmond, Wash., campus.

The release candidate software follows a number of community technology previews, and checks off a few checkboxes on its way to general availability, which is expected this year.

SQL Server 2017 RC1 is notable for supporting Active Directory authentication, transparent layer security for encryption of client-server transmission over networks, and tweaks to cluster node settings.

While one-to-one function parity between the Windows and Linux versions of SQL Server is not immediately on tap, the new Linux version offers a sizable portion of what is familiar in SQL Server for Windows.

Some advanced software development is behind the port to Linux. The company tapped into Microsoft Research project Drawbridge to provide a Platform Abstraction Layer (PAL), and some limited changes to its underlying SQL Server engine, to allow existing Windows dependencies to be used without change for Linux.

SQL Server for Linux in context

"I have a lot of confidence in the stability, scalability and capability of SQL Server for Linux, simply because I have seen it on Windows and in Azure already," said John Martin, a Microsoft MVP and product manager at SentryOne, a maker of performance monitoring and optimization software for Microsoft SQL Server and other platforms.

Martin credits Microsoft's use of the PAL for its port of the SQL Server codebase for a Linux version of SQL Server. A lot of added work has gone into running SQL Server for Linux, he noted.

[SQL Server for Linux] is not a second-class citizen.
Allan Hirtmanaging partner, SQLHA LLC

"Tier 1 features like failover cluster instances and availability groups shows this is a serious move," he said. Microsoft's move to feature parity between Standard and Enterprise SQL Server editions is another plus, Martin said.

While SQL Server 2017 is coming quickly on the heels of SQL Server 2016, and many of the enhancements are minor, "Linux support in itself is enough to justify the release," according to Michael Otey, consultant, author and contributor to SearchSQLServer.com.

That Linux support will be important, especially in large organizations that have heterogeneous deployments, Otey said, adding that the move "dovetails nicely" with other Microsoft efforts to expand support of open source software.

Not surprisingly, the first Linux version of SQL Server lags its big server brother in several areas. Just a partial list of unsupported features that contrast SQL Server for Windows with SQL Server for Linux includes Stretch Database, PolyBase, Analysis Services and Master Data Services. Still, the mere fact that Microsoft is not shunning Linux is significant.

"Microsoft SQL Server for Linux is not full featured. But you really wouldn't expect that, considering it is the first release," Otey said.

Beyond the Linux port

Although they are somewhat less vivid than changes in last year's SQL Server 2016 release, there are important new elements beyond often highlighted Linux support.

For Allan Hirt, managing partner of SQL Server consulting firm SQLHA LLC, which is especially focused on mission-critical implementations, attention to the new Linux version of SQL Server should not obscure advances in the Windows version of the database server.

An advance particularly useful for high availability, he said, is full support of the Always On Availability Groups feature in SQL Server 2017 for applications using the Microsoft Distributed Transaction Coordinator.

There are other availability improvements, including the introduction of cluster types for availability groups, the ability to control behavior for synchronous replicas in an availability group, and support for the major availability features on Linux, he said.

This is valuable, Hirt said, because IT shops of all sizes are putting increasing emphasis on availability for their data no matter what platform it resides on.

Gaining high availability, or HA, "is not all about SQL Server," he adds. "These new capabilities are only part of the story, because your entire solution has to work in concert to make sure you have availability."

SQL Server DBAs will encounter different challenges in setting up highly available database servers on Linux than they did on Windows, he said. But challenges they encounter will mainly be due to the differences between the operating systems, especially when it comes to clustering.

"In either case, availability groups are availability groups. And failover is failover. At its core, it's just SQL Server whether you are running on Windows Server or Linux," Hirt said.

Still, SQL Server for Linux is an important step, and the level of support from Microsoft is significant. In Hirt's words, "It is not a second-class citizen."

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