Category: Teradata

Cloud Computing and Data Warehousing: Part 1 – The Architectural Issues

My apologies… I was playing with the iPad version of WordPress and accidentally published a very rough outline/first draft of this post. I immediately un-published it… but not before subscribers were notified that there was a new post.

I wonder about the idea that data warehousing is suited to operate in the cloud? This was prompted by Paraccel‘s venture to deploy on the Amazon EC2 cloud infrastructure. Lets work through the architectural implications…

Here are the assumptions I’ll take into this exploration:

  1. A shared-nothing architecture is required to scale.
  2. Cloud infrastructure is cost-effective when the infrastructure is under-utilized and workloads can be consolidated to achieve full utilization… and not so cost-effective when the infrastructure is highly utilized. This is because applications can easily share underutilized resources in the Cloud.
  3. Cloud infrastructure is justified when the workload is inconsistent and either CPU or storage requirements fluctuate widely over the business cycle. This is because a Cloud is elastic and can easily flex as the requirements fluctuate. Cloud computing may not be well suited to static workload requirements.

You can probably see where I’m going with this from the assumptions.

In the end I’ll suggest that there is a database architecture that is suited to warehousing and cloud computing… but let me build to that.

Before I start let me also be clear that I am talking about the database infrastructure… not the application/BI infrastructure required for data warehousing. The BI and ETL components are perfectly suited to cloud computing… they reflect a workload that, in general, runs on under-utilized hardware with BI running during the day and ETL running at night. I have suggested this to my current employer… but alas, I am neither King nor a member of Court.

So in Part 1 let me discuss my first two assumptions and the implications… In Part 2 I’ll discuss data warehousing and elasticity… In Part 3 I’ll consider the Paraccel/Amazon collaboration and in Part 4 I’ll wrap up and consider several new things coming that may change the equations.
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I’ll not work too hard to justify my first assumption… I think that it is well-understood that a shared-nothing architecture provides the best possible approach to scale out. Google and others use this approach to scale to hundreds of petabytes of data and Teradata, Greenplum, Netezza, Paraccel, SAP HANA, and others use it in the data warehouse space. Exadata uses a hybrid approach that scales I/O in a shared-nothing-like storage subsystem… but fails to scale as it passes data to the RAC layer (see Kevin Closson here on the subject).

But the implications are significant for our cloud discussion. First, cloud infrastructure is designed to support general client-server or web-server based commercial computing requirements. A shared-nothing database cluster is a specialized infrastructure optimized for database processing. Implementing the specialized problem on the generalized infrastructure is possible, but sub-optimal. Next, cloud computing requires, more or less, a shared storage subsystem. A shared-nothing architecture shares nothing. Implementing a shared-nothing database on a shared storage subsystem is possible, but sub-optimal.

I believe that the second assumption is also pretty straightforward. The primary rationale for cloud computing comes from the recognition that many data centers deployed applications on servers that were not fully utilized. By virtualizing the hardware on a cloud platform the data center could better service the applications with fewer hardware resources and therefore less cost.

So… in order for cloud computing to be a perfect fit we need to observe a data warehouse database workload with underutilized hardware infrastructure… You might ask yourself… are there underutilized hardware resources upon which my EDW is built? In most cases I believe that the answer to this question will be “no”. Almost every EDW I’ve seen is over-burdened… stretched… with users demanding more and more resource… more data, more users, more queries, deeper queries drive the resource requirements up exponentially. The database is swamped all day with queries and swamped all night by ETL and reporting tasks.

So let’s end this blog concluding that there is a problematic architectural mismatch between a shared cloud and a shared-nothing implementation… and that if your warehouse database platform is highly utilized then there may be little benefit from implementing a warehouse in the cloud.

See Part 2 here…

More on Exalytics Capacity…

I found myself wondering where did the rule-of-thumb for Exalytics  that suggests that TimesTen can use 800GB of a 1TB memory space… and requires 400GB of that space for work tables leaving room for 400GB of user data… come from (it is quoted everywhere… here is an example… see question #13).

Sure enough, this rule has been around for a while in the TimesTen literature… in fact it predates Exalytics (see here).

Why is this important? The workspace per query for a TPC-A transaction is very small and the amount of time the memory is held by a TPC-A transaction is very short. But the workspace required by a TPC-H query is at least 10X the space required by a TPC-A query and the duration of a TPC-H query is at least 10X the duration of a TPC-A query. The result is at least 100X more pressure on memory utilization.

So… I suspect that the 600GB of user data I calculated here may be off by more than a little. Maybe Exalytics can support 300GB of user data or 100GB of user data or maybe 60GB?

Note that this is not bad… all of this pressure on memory is still moved to Exalytics from the Exadata RAC subsystem… where memory is dear.

As a side note… it is always important to remember that the pressure on memory is the amount of memory utilized times the duration of the utilization. This is why the data flow architecture used in modern databases like Greenplum are effective. Greenplum uses more memory per transaction but it holds the memory for less time by never (almost) writing it to disk. This is different from older database architectures like Teradata and Oracle which use disk to store intermediate results… lowering the overall amount of memory required but increasing the duration of the query. More on this here…

More on Big Data… and on Big Data Analytics… and on a definition of a Big Data Store…

After a little more thinking I’m not sure that Big Data is a new thing… rather it is a trend that has “crossed the chasm” and moved into the mainstream. Call Detail records are Big Data and they are hardly new. In the note below I will suggest that, contrary to the long-standing Teradata creed, Big Data is not Enterprise Data Warehouse (EDW) data. It belongs in a new class of warehouse to be defined…

The phrase “Big Data” refers to a class of data that comes in large volumes and is not usually joined directly with your Enterprise Data Warehouse data… even if it is stored on the same platform. It is very detailed data that must be aggregated and summarized and analyzed to meaningfully fit into an EDW. It may sit adjacent to the EDW in a specialized platform tailored to large-scale data processing problems.

Big Data may be data structured in fields or columns, semi-structured data that is de-normalized and un-parsed, or unstructured data such as text, sound, photographs, or video.

The machinery that drives your enterprise, either software or hardware, is the source of big Data. It is operational data at the lowest level.

Your operations staff may require access to the detail, but at this granular level the data has a short shelf life… so it is often a requirement to provide near-real-time access to Big Data.

Because of the volume and low granularity of the data the business usually needs to use it in a summarized form. These summaries can be aggregates or they can be the result statistical summarization. These statistical summaries are the result of Big Data analytics. This is a key concept.

Before this data can be summarized it has to be collected… which requires the ability to load large volumes of data within business service levels. The Big Data requires data quality control at scale.

You may recognize these characteristics as EDW requirements; but where an EDW requires support for a heterogeneous environment with thousands of data subject areas and thousands and thousands of different queries that cut across the data in an ever-increasing number of paths, a Big Data store supports billions of homogeneous records in a single subject area with a finite number of specialized operations. This is the nature of an operational system.

In fact, a Big Data store is really an Operational Data Store (ODS)… with a twist. In order to evaluate changes over time the ODS must store a deep history of the details. The result is a Big Data Warehouse… or an Operational Big Data Store.

The Best Data Warehouse Spin of 2011

At this time of the year bloggers everywhere look back and reflect. Some use the timing to highlight significant achievements… and it is in the spirit that I would like to announce my choice for the best marketing in the data warehouse vendor space for 2011.

Marketing is a difficult task. Marketeers need to walk a line between reality and bull-pucky. They need to appeal to real and apparent needs yet differentiate. Often they need to generate spin to fuzz a good story by a competitors marketing or to de-emphasize some short-coming in their own product line.

Below is a picture taken on the floor of a prospect where we engaged in a competitive proof-of-concept. The customer requested that vendors ship a single rack configuration… and so we did.

But the marketing coup is that the vendor on the right, Teradata, told the customer that this is a single rack configuration and that they are in compliance. The customer has asked us if this is reasonable?

This creative marketing spin wins the 2011 award going away… against very tough competition.

I expect this marketing approach to start a trend in the space. Soon we will see warehouse appliance vendors claiming that 1TB = 50TB due to compression… or was that already done this year?

Sorry to be cynical… but I hope that the picture and story provide you with a giggle… and that the giggle helps you to start a happy holiday season.

– Rob Klopp

Teradata’s Excellent Memory Management… and Poor Memory Utilization

I was recently surprised to hear from a prospect that Teradata’s memory management was considered a differentiator over Greenplum. This is not because of bad information… Teradata probably does have better memory management… but they have better memory management because they use memory less efficiently than Greenplum. Let me explain…

First let’s be clear… the utilization of memory is not measured by the amount of memory required… but by the amount required times the amount of time it is required. Think about it… if you have a query that requires 16MB of memory and holds it for 1 second… and another query that requires 4MB of memory and holds it for 4 seconds… the effective memory utilization is the same.

Greenplum uses pipelining to flow data from step to step in the query plan. Teradata writes the results from each step in the query plan to disk, to a spool file. This architectural difference allows Greenplum to complete any single query in a small fraction of the time that Teradata requires… as Teradata pays the cost of writing results after each step and of reading these results into the subsequent steps add up. The result is that Teradata uses a smaller memory footprint for each query… but holds the memory significantly longer… resulting in relatively poor memory utilization.

Note that this is not really bad design by Teradata… it is just old design. Once upon a time the servers Teradata ran on had only a little memory… as little as 32MB… so they had to spool data to disk to make it all fit. Greenplum is designed for modern processors with 100X more memory… and we use that memory effectively to get queries in and out as fast as possible.

By the way, as a side effect Greenplum does not require management of spool space… so this sysadmin task is eliminated.

So… Teradata does tightly manage memory… but this is not an advantage… they manage it tightly because they have to.

The Worst Data Warehouse in the World

So far this blog has focused on issues related to database architecture… so this title might not seem on message. But architecture has implications.

The aim of any BI system is to support the decision-making process of the business. BI infrastructure is clearly a success when your company learns to make fact-based decisions as part of the day-to-day operation of the business. The best data warehouse in the world would be one that provides such effective decision support that the business gains a competitive advantage over the competition.

But I often run into companies where sweet success has turned sour. Why, because in these sour situations the BI eco-system cannot keep up. In these bad cases the best data warehouse in the world becomes the worst.

Usually the problem comes in one of two flavors: either the required decision support is unavailable in time to make a decision, or the eco-system cannot extend to support new business opportunities.

The first case usually shows up during periods when decision-making increases: during seasonal peaks in business. The second appears when the business grows: after a merger or when a new product is introduced. In both cases the cost of the failure is significant.

But these worst cases do not happen out of the blue. They creep up on you. There are symptoms. Often the first symptom is when the nightly reporting process starts missing its service level targets. That is, the nightly load of the warehouse and the refresh of the indexes, materialized views, the summary tables, the cubes, and the marts; and then the running of reports cannot complete in the batch window. This is followed by slow response in your online query processing as the nightly process creeps into the day. Then, the business asks for more users and/or for more data to be added and the problem grows… until decision-making is delayed or unsupported altogether.

Sadly, this problem is avoidable and the solution is well understood. All that is required is a scalable foundation that can extend through the addition of relatively inexpensive hardware. If you could easily add storage and compute then as the constraints hit you can scale up.

A shared nothing architecture scales. We have examples at Greenplum of production systems that scale from hundreds of gigabytes to thousands of terabytes… and other shared nothing vendors: Teradata and Netezza at least, can boast the same. When our customers run out of gas we add hardware. And the architecture scales bigger still… shared nothing is the foundation for all web scale data base technology… scaling to hundreds of petabytes.

So why do companies build, and continue to build, on shared memory systems with built-in limits? Because… they continually underestimate the growth in data… the failure is a failure of vision (consider the name “Teradata”… selected when a terabyte was considered nearly unreachable). Data does not just grow, it explodes in leaps and bounds as technology advances.

But let’s be real… Why do companies really select limiting infrastructure? Because they mistakenly believe that they can build BI infrastructure on technology designed for OLTP… and they already have DBAs trained on this technology who heavily influence the decision. Or, they have an enterprise license for the OLTP database and they want to save some money.

I imagine that I’ve made my point. The worst data warehouse in the world is a warehouse that constrains your business… one that cannot scale as the demand for data and decision support grows… one that costs you hundreds of thousands of dollars in staff time with every change… one that is tuned to the breaking point, rather than robust.

Why would anyone ever put their business at risk like this?

Greenplum and Teradata: Simliar Architecture, Different Strategies

Hardware systems, servers and network fabric, provide the foundation upon which all shared-nothing database management systems rest. Hardware systems are a major contributor to the overall price/performance and total cost of ownership for a data warehouse platform. This blog considers the hardware strategies of EMC/Greenplum: applying the idea of using common, off-the-shelf (COTS) components to build a competitive foundation; and Teradata: developing a proprietary hardware system by tightly integrating components.

Strategies

The Teradata hardware strategy is simple to describe. They expend R&D dollars to couple low-level technologies into a tightly integrated system. Their servers are custom-designed within a set of guidelines that allows both the LINUX and Microsoft Windows operating systems to execute there. Their network fabric is highly proprietary, using cycles within the fabric to offload sort/merge data processing from the server CPU.

In other words, Teradata believes that the time and effort required to engineer an integrated proprietary offering will improve the performance of their offering enough to offset the cost.

EMC and Greenplum have taken a different approach. They have elected a strategy that leverages off-the-shelf servers offered by hardware vendors like Dell or HP, and network switches from vendors like Brocade, Arista, and Cisco. They have elected to expend few dollars on hardware design and development and to leverage the R&D investments made by these other vendors. In other words, Greenplum believes that the advantages in price and performance provided by using off-the-shelf hardware provides a sustainable advantage.

Price

The lower costs associated with Greenplum’s strategy clearly provide an advantage. Greenplum does not have to expend to design and manufacture custom hardware. The manufacturing costs may not be significant, but the staff costs required by the Teradata strategy must affect the price. Clearly the Greenplum strategy provides an advantage on the price side.

Performance

The Teradata strategy has to be about performance… so lets speculate:

  • How much of a performance increase might their integration provide on the server-side?
  • How much of a performance increase might their integration provide on the network side?

In the days before there was a microprocessor based enterprise server market, Teradata could gain substantially here. Microprocessors were built for personal computing and not designed for the high-availability and high-performance requirements in an enterprise. Teradata had much to gain from building rather than buying server.

But today, there is little to gain from a highly customized design. The requirement to run standard LINUX and Windows operating systems limit their ability to innovate and the resulting servers have to be very similar to those built for off-the-shelf enterprise servers. There is little or no performance advantage here.

On the network side, there once was a distinct advantage to Teradata’s ByNet. It was both faster than available off-the shelf switches and it offloaded cycles from the under-powered CPU. Today, however, there are plenty of cheap, fast switches… so the speed advantage has disappeared. Worse still, the introduction of multi-core CPUs have eliminated the advantage of the in-the-switch sort/merge that makes ByNet unique. CPU is inexpensive these days.

The bottom line: it is unclear if the Teradata hardware strategy affords them a performance advantage.

Cost of Ownership

An argument could be made that supporting COTS hardware is inherently less expensive than supporting a Teradata cluster. But there is a more substantial savings that is clear.

Every 2-3 years, as newer Teradata technology obsoletes your currently installed cluster the value of the current hardware goes to zero and the cost of ownership goes up significantly. The costs of this are especially high when you are required to add several nodes to accommodate growth as Teradata refreshes their technology. You may have to buy servers that are already obsolete.

With Greenplum, your current cluster is built from general-purpose servers that are re-purposed with ease. In fact, since the nodes in a Greenplum cluster are usually high-end servers, customers often cycle new technology into their data warehouse and cycle the old servers out into their server farm. The result is a higher performance warehouse and full use of all of the server technology.

A Final Word

The words “proprietary hardware” are sometimes thrown around as an insult. But Teradata’s proprietary approach is based on the belief that a tightly integrated configuration adds benefit to offset the costs. Greenplum believes that today the enterprise server and the network switch vendors have matured their products to the point where off-the-shelf technology can match or exceed the performance of custom hardware… at a significantly reduced cost. You may have an opinion or you may wait to see how the benchmarks, the proof-of-concepts, and the market decide… but its interesting to understand the differing approaches.

Co-processors and database machines: Intel, Netezza, and Teradata

Intel recently announced a change in direction regarding the use of special hardware co-processing to support RAID. This change is relevant to vendors of data warehouse appliances like Netezza, and to a smaller extent, Teradata, who both use co-processors to offload processing. A report on the Intel announcement is here: http://www.theregister.co.uk/2010/09/15/sas_in_patsburg/ . In short, Intel says that because multi-cores provide so much compute for so little cost it just does not make sense to build a special co-processor to support the RAID function.

What, you may ask, does this have to do with Netezza and Teradata. The answer is that both companies have built database machines that use co-processors more-or-less. And Intel’s conclusion that multi-cores obsolete co-processors significantly affects their value proposition to the market.

In the case of Netezza the significance is considerable. Netezza conceived the FPGA-based architecture when compute was expensive relative to I/O. A FPGA provided a way to add compute power at a low-cost point. But according to Intel this changed as multi-core technology matured. Further, as  the Intel processing line adds even more cores, the value of a FPGA co-processor becomes less still.

In the case of Teradata the issue is more manageable. The original Teradata Y-Net and their current BYNET interconnect offloads the merge process from the CPU to the interconnect. Back when Teradata ran on 8086 cores from Intel this was significant and it formed a cornerstone of Teradata’s value proposition. Today, the value of BYNET is diminished and one could imagine Teradata dropping it altogether sometime in the future for a less proprietary network fabric.

Please do not think that I am suggesting that multi-cores make either Teradata or Netezza obsolete. They are both formidable technologies. But multi-cores will reduce the price/performance advantage that co-processing once afforded in favor of database servers that do not use co-processing like Exadata, Greenplum, and DB2.

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