SAP ADAPTIVE SERVER ENTERPRISE SP130, CLUSTER EDITION

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Peter Thawley

Vice-President & Chief Technology Advisor CTO Office, SAP Global Customer Operations

TABLE OF CONTENTS

IN SEARCH OF CONTINUOUS AVAILABILITY ... 3

ADAPTIVE SERVER ENTERPRISE CLUSTER EDITION ... 4

DEPLOYMENT SCENARIOS FOR ASE CLUSTER EDITION... 5

Two Node, Active-Passive (1+1) ... 5

Multi-Node, Active-Passive (N+1) ... 5

Multi-Node, Active-Active Consolidation ... 6

SAP Adaptive Server® Enterprise SP130, Cluster Edition

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Business executives know that today’s Darwinian business climate favors lean, efficient

organizations. Given Information Technology (IT) often accounts for a significant portion of an enterprise’s budget, CxO’s are increasingly scrutinizing IT costs. Gone are the days when ROI could be proven by soft, fluffy metrics. Today’s IT projects simply don’t get approved unless they materially contribute to top-line or bottom-line growth. Consequently, IT executives are focused on looking at ways to contribute to these business imperatives. Although every business

approaches these mandates somewhat differently, there are clearly some common priorities the vendor community is being driven to help solve.

The first priority, Consolidating and Standardizing IT’s Infrastructure, has been has been underway for several years. For many, this has meant moving small applications servicing a limited set of people off their own small servers onto a larger server platform which have sufficient capacity to host many different applications. Although this resulted in dramatically less servers to manage, the ROI was at times questionable because the cost of these larger Symmetric

Multiprocessor (SMP) UNIX® servers was significantly higher. With the rapidly increasing

performance of commodity hardware, this trend is growing but shifting away from proprietary SMP because of the cost savings from Intel® based hosts.

The second priority, Improving IT Continuity and Security, can also be considered a “work-in-progress” since the Internet became an important channel for businesses and customers to

communicate. Yet, achieving “five nines” (99.999% uptime) requires more than just hardware and high availability. The 24x7 nature of the global businesses dictate systems provide continuous availability. Businesses missing this mark often risk losing more than their customers’ patience – they risk losing their customers altogether! The cold hard fact is that customer loyalty is virtually non-existent for many businesses because of global competition. At the first hint of trouble, many people simply go to the next vendor. In essence, with your customers’ just one click away from your competition, service-levels are more important than ever.

The third priority, Instituting a More Flexible IT Infrastructure, is grounded in some very appealing, albeit sometimes over-hyped, ideas. Fifteen years ago, the buzz around grid

computing and utility computing was the focus. Of course now we talk about this priority in the context of virtualization and cloud computing. One of the greatest interests to today’s IT

Executives is the ability to utilize multiple, independent computer resources as a shared resource where workload can be shifted around and augmented as needed in support of service-level agreements (SLAs) to the business.

With more applications requiring continuous availability and data centers being overtaxed for power, cooling and space, IT requires innovative, practical, and dependable solutions. To that end, SAP has invested heavily to further enhance SAP ASE Cluster Edition to help IT organizations make tangible and practical gains with these important priorities.

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ASE Cluster Edition, first released in 2009, supports shared disk cluster hardware configurations to provide concurrent access to one or more databases from multiple server hosts. Many of today’s deployments utilize clusters of 4-8 nodes. Figure 1 to the right depicts a representative deployment environment for ASE Cluster Edition.

Figure 1 – ASE Cluster Edition Environment

Clustered database systems present themselves as a single system to applications which provides significant advantages for both continuous availability and operational flexibility. ASE Cluster Edition provides patent-pending Virtualized Resource Management™ (VRM) to maximize availability by enabling applications to transparently fail-over and fail-back during both planned and unplanned outages as well as improving the systems’ ability to cope with higher than normal peak load requirements by enabling on-line migration of workloads from one node to another. While some vendors argue that clustered databases are the “best” solution for scale-out of a single application, Sybase (now an SAP Company) is the only RDBMS vendor to have built out both shared-nothing and shared-disk cluster databases. I will tell you from personal experience that linear scalability across even a modest number of cluster nodes for a single high performance OLTP enterprise application is effectively impossible, unless some of the “ACID” tenants of database processing are ignored as are done in the NoSQL/NewSQL database engines used in some of the “web-scale” scenarios such as the Amazon’s and Facebook’s of the world.

Linear scalability of enterprise OLTP databases is constrained by the requirement to ensure the integrity of the data in-memory across multiple physical hosts. While this issue, known in computer science as “distributed cache coherency”, can be minimized in some use-cases and businesses through careful data partitioning, it is very complex and filled with risk. More

realistically, it is unnecessary in 99% of applications today because performance requirements are not that high!

While ASE Cluster Edition technically supports scale-out processing, our customers find the complexity and processing overhead outweigh the benefits. Even for the remaining 1% of applications that truly require such extreme performance, hardware vendors are scaling the amount of CPU and memory in a single symmetric multiprocessing server to levels that most of these can be serviced from a single database server. For example in today’s commodity hardware, a single server costing about US$60,000 supports 120 cores and 2 terabytes of memory. How many of your applications need that many cores and that much memory?

In ASE Cluster Edition SP130, we have specifically optimized for the mainstream use cases of continuous availability and operational flexibility. DBA’s can choose to configure a database such that processing requests from applications are always serviced by one cluster node at a time. Known as “single instance databases”, this characteristic allows ASE Cluster Edition to eliminate a hugely expensive code path to support distributed locking and memory management across nodes. Using this approach does not preclude any of the core functionality around fail-over / fail-back across nodes or online workload migration.

SAP Adaptive Server® Enterprise SP130, Cluster Edition

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Shared-disk cluster databases are ideally suited to applications having any of the following characteristics:

 A low tolerance for downtime;

 Business requirements for near instantaneous fail-over of database processing upon an unplanned outage (i.e., an HA requirement for zero-data-loss and an RTO close to zero);

 Small or non-existent maintenance windows with which to handle planned downtime activities like upgrading hardware or patching operating systems;

 Requirements for a more cost-effective or application-aware high availability solution than traditional operating system based cluster-ware solutions provide;

 You support a large number of small applications, many of which run on their own servers today.

With these characteristics in mind, we expect the following deployments patterns for ASE Cluster Edition.

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Despite the marketing hype and advertisements depicting clusters as 100’s of database servers in a grid being the next generation mainframe, many HA deployments today are simple two-node configurations with an active node performing all the work and a passive standby node waiting in case the active node dies for any reason. Although not a cost-effective, its’ simplicity to set up and manage make it more popular than traditional cold failover techniques. The main drawback of this approach is its’ cost effectiveness – having a passive standby node idle, producing little except an electricity bill, does not make CFO’s happy.

Figure 2 – Active-Passive Database Cluster

MULTI-NODE, ACTIVE-PASSIVE (N+1 AND N+M)

passive “standby” node across a number of separate database servers. This model greatly improves the economics of a cluster by

amortizing the cost of the additional standby node used in fail-over over a larger set of systems running on the cluster. The main drawback of this approach is that if multiple nodes fail, a single standby may become overloaded quickly. The easiest solution to this would be to add multiple passive fail-over nodes to cover a multiple failure scenario in more of a N+M Availability model (“N” Active Nodes and “M” Passive Nodes).

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When one looks across an enterprise’s IT portfolio, it is clear that there is a wide variety of applications supported. While each of us have some number of “tier 1” applications which have significant SLAs around performance and availability, there are also a significantly larger

number of applications that either relatively small or have less stringent SLA’s. Several years ago, there was a significant effort to consolidate these many small systems onto larger multi-core servers. While this approach certainly delivers on the first priority noted at the top of this paper to “consolidate and standardize IT infrastructure”, it misses the mark entirely on either providing improved business continuity or a more flexible IT infrastructure.

This is where ASE Cluster Edition has the greatest potential to provide significant business value. Not only can ASE Cluster Edition provide a shared database platform on which to

consolidate many applications and their associated databases, but it can automatically provide a level of high availability without additional cost to all applications running on it. This is achieved through transparent fail-over of applications connections to the database and faster database fail-over with an optimized shared disk database cluster than traditional HA models. In Figure 4 below, we see how eight different ASE Servers, each running on their own host, could be consolidated onto half as many hosts while still leaving sufficient capacity on each host to provide fail-over support for other instances. Effectively, this means IT can provide high availability support to applications as additional benefit without additional cost or effort.

SAP Adaptive Server® Enterprise SP130, Cluster Edition

Reaching the bar of Continuous Availability while still maintaining the manageability and ease of use for which ASE is known takes a lot more than just ultra-fast failover. ASE Cluster Edition allows the cluster to grow and shrink dynamically as needed to ensure business service levels can be met whenever necessary as well as sophisticated load balancing and workload management facility that allows DBAs to move workload from one cluster node to another. This is facilitated by a patent-pending connection redirection and context migration capability where network

connections can be moved from one host to another at points in the application workload (e.g., after transactions’ commit) that make sense.

Perhaps the most significant area of innovation in ASE Cluster Edition to help you protect your business service levels, maximize resource utilization as well as reduce your IT infrastructure costs is the Virtualized Resource Management™ technology. Figure 5 below depicts an example where an application “A” experiences a higher than average peak load. Rather than impact the SLAs to both this application and other applications on that instance (B), a DBA could simply choose to move the running application B to another host temporarily, providing extra capacity to application A while ensuring application B isn’t impacted. By allowing DBAs to associate specific cluster nodes to applications, not only can you allocate capacity based on business priorities, but it also provides the foundation to dynamically shift resources between applications as needed.

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ASE Cluster Edition builds on ASE’s reputation for reliability and lower costs by delivering a

database infrastructure that enables IT to reduce data center costs through better utilization, drive application availability much closer towards 100%, and create a flexible data infrastructure for future business growth. The recently released ASE SP130 Cluster Edition adds significant

optimizations to the underlying interconnect layer that eliminates the overhead typically associated with clustered databases solutions. This innovation opens the door for IT organizations to

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