Refactoring Databases P2.75: REST and ORB Thoughts

I’m riffing on database design and modeling in an agile methodology. In the previous post here I suggested that we might cheat a little and design database schemas 2-4 weeks in advance of their use… further, I suggested that to maximize agility we should limit the design to a conceptual schema. In this post I’m going to limit the scope little more by considering the use of a database in a restful application.

I am not going to fully define the REST architecture here… but if you are a systems architect you should know this inside and out… what I will say is that sometimes, in order to build a RESTful application, you will find yourself using the database to store the application state. What I want to say here is that when the application stores state in a database that must persist across boundaries in your business process… but that is not required to persist across business processes… then you do not need to model this. Let the programmers do their worst. In this case database tables play the role of working storage (a very old term that dates me… at least I did not say “Data Division”)… and programmers need to be completely free to add and subtract data elements in their programs as required.

I also have a question for the architects out there…

When programmers touch relational data they typically go through one or more abstractions: maybe they call an XML-based RESTful web service… or maybe they write the service themselves and in the service call an ORB-thingie like Hibernate. I’ve seen terrible schema signs that result from programmers building to an object model without looking at the resulting relational model out of the other end. So… when we assign data architects to build a relational schema to underlie an object-oriented programming language… should we architect up the stack and deliver the relational schema, the ORB layer, and/or the RESTful CRUD services for the objects? We are starting down that path… but I thought that I would ask…

Refactoring Databases P2.5: Scoping the Cheats

One of the side-effects of the little cheat posted here is that, if we are going to design early we have to decide what we will design early… and this question has two complications. First, we have to ask ourselves how detailed do we design before the result becomes un-agile? Next, we have to ask ourselves if we should design up the stack a little? My opinions will be doggedly blogged in this post.

I will offer two ends of a spectrum to suggest a way to manage the scope of your advance design cheat. Let me remind you that the cheat suggests that you look at the user stories that will be sprinted on next and devise the schema required from those stories… and maybe refactor the existing schema a little (more in the next post) no more than that.

On one side we may develop a complete design with every detail specified: subject areas, tables, columns, data types, and domains. The advantage here is that the code developers have a spec to code to and these could increase velocity. But the down side is that developers will be working with users to adjust the code in real-time. If the schema does not fit the adjustments then you may be refactoring the new stuff and velocity may decrease.

The other side of the spectrum would have database designers just build a skeleton; a conceptual schema with subject areas, tables and primary keys for each table. This provides a framework that corrals the developers without fencing them in so tight that they cannot express agility.

Remember that the object here is to reduce refactoring without reducing agility…

IMO the conceptual model approach is best. Let’s raise free range software engineers who can eat bugs in the wild rather than be penned in. The conceptual model delimits the range… a detailed schema defines a pen.

There is one more closely related topic for the next post… how do we manage transient objects in a restful application?

Refactoring Databases P2: Cheating a Little

In this post I am going to suggest doing a little design a little upfront and violating the purity of agility in the process. I think that you will see the sense.

To be fair, I do not think that what I am going to say in this post is particularly original… But in my admittedly weak survey of agile methods I did not find these ideas clearly stated… So apologies up front to those who figured this out before me… And to those readers who know this already. In other words, I am assuming that enough of you database geeks are like me, just becoming agile literate, and may find this useful.

In my prior post here I suggested that refactoring, re-working previous stuff due to the lack of design, was the price we pay to avoid over-engineering in an agile project. Now I am going to suggest that some design could eliminate some refactoring to the overall benefit of the project. In particular, I am going to suggest a little database design in advance as a little cheat.

Generally an agile project progresses by picking a set of user stories from a prioritized backlog of stories and tackling development of code for those stories in a series of short, two-week, sprints.

Since design happens in real-time during the sprints it can be uncoordinated… And code or schemas designed this way are refactored in subsequent sprints. Depending on how uncoordinated the schemas become the refactoring can require a significant effort. If the coders are not data folks… And worse, they are abstracted away from the schema via an ORM layer, the schema can become very silly.

Here is what we are trying to do at the Social Security Administration.

In the best case we would build a conceptual data model before the first sprint. This conceptual model would only define the 5-10 major entities in the system… Something highly likely to stand up over time. Sprint teams would then have the ability to agile define new objects within this conceptual framework… And require permission only when new concepts are required.

Then, and this is a better case, we have data modelers working 1-2 sprints ahead of the coders so that there is a fairly detailed model to pin data to. This better case requires the prioritized backlog to be set 1-2 sprints in advance… A reasonable, but not certain, assumption.

Finally, we are hoping to provide developers with more than just a data model… What we really want is to provide an object model with basic CRUD methods in advance. This provides developers with a very strong starting point for their sprints and let’s the data/object architecture to evolve in a more methodological manner.

Let me be clear that this is a slippery slope. I am suggesting that data folks can work 2-4 weeks ahead of the coders and still be very agile. Old school enterprise data modelers will argue… Why not be way ahead and prescribe adherence to an enterprise model. You all will have to manage this slope as you see fit.

We are seeing improvement in the velocity and quality of the code coming from our agile projects… And in agile… code is king. In the new world an enterprise data model evolves evolve based on multiple application models and enterprise data modelers need to find a way to influence, not dictate, data architecture in an agile manner.

How DBMS Vendors Admit to an Architectural Limitation: Part 2 – Teradata Intelligent Memory

This is the second post (see Part 1 here) on how vendors adjust their architecture without admitting that the previous architecture was flawed. This time we’ll consider Teradata and in-memory….

When SAP HANA appeared Teradata went on the warpath with a series of posts and statements that were pointed but oddly miscued (see the references below). According to the posts in-memory was unnecessary and SAP was on a misguided journey.

Then Teradata announced Intelligent Memory and in-memory was cool. This is pretty close to an admission that SAP was right and Teradata was wrong. The numbers which drove Teradata here are compelling… 100K-200K ns to access an SSD device or 100 ns to access DRAM… a 1000X reduction… and the latency to disk is 100X worse than SSD.

Intelligent Memory was announced shortly after the release of Teradata’s columnar table type. Column-orientation is important because you need a powerful approach to compression to effectively use an expensive memory resource… and columnar provides this. But Teradata, like Greenplum, extended a row-based engine to support columns in order to get to market quick… they hoped to get 80% of the effectiveness of in-memory with only 20% of the engineering effort. The other 20% comes when you develop a new engine that fully exploits the advantages of a columnar architecture. These advanced exploits allow HANA, DB2 BLU, and Oracle 12c to execute directly on columnar data thereby avoiding decompression, fully utilizing the processor caches, and allowing sets to be operated on by super-computing vector-processing instructions. In fact, Teradata really applied the 50/20 rule… they gained 50%, maybe only 40%, of the benefits with their columnar and Intelligent Memory features… but it was easy to deploy what is in-effect an in-memory cache over their existing relational engine.

Please don’t jump to the wrong conclusion here… Intelligent Memory is a strong product. If you were to put hot data in memory, cool data in Teradata-on-SSD-or-Disk, and cold data in Hadoop and manage them as one EDW you could deploy a very cost-effective platform (see here).

Still, Teradata with Intelligent Memory is not likely to compete effectively against HANA, BLU, or 12c for raw performance… so there will be some marketing foam attached and an appeal for Teradata shops to avoid database apostasy and stick with them. You can see some of the foam in the articles below.

A quick aside here… generally a DBMS should win or lose based on price/performance. The ANSI standard makes a products features nearly, not completely but nearly, irrelevant. If you cannot win on price/performance then you blow foam. When any vendor starts talking about things like TCO you should grab your wallets… it is an appeal to foaminess to hide a weakness. I’m not calling out Teradata here… this is general warning that applies to every software vendor.

Intelligent Memory is a smart move. While it may not win in a head-to-head POC… it will be close-ish… close enough to keep the congregation in their pews. As readers know, I am not a big fan of technical religiosity… being a “Teradata-shop” is lazy… engineers we should pick the best solution and learn it. The tiered approach mentioned three paragraphs up is a good solution and non-Teradata shops should be considering it… but Teradata shops should be open to new technology as well. Still, we should pick new technology with a sensitivity to the cost of a migration… and in many cases Intelligent Memory will save business for Teradata by getting just close enough to make migration a bad trade-off. This is why it was so smart.

Back to the theme of these posts… Teradata back-tracked on the value of in-memory… and in the process admitted-without-admitting a shortcoming in their architecture. So it goes…

Next we will consider whether you should be building data warehouses on z/OS using DB2 or the DB2 Analytics Accelerator aka Netezza.

References

Database Fog Blog

Other

Dynamic Late Binding Schemas on Need

I very much like Curt Monash’s posts on dynamic schemas and schema-on-need… here and here are two examples. They make me think… But I am missing something… I mean that sincerely not just as a setup for a critical review. Let’s consider how dynamism is implemented here and there…so that I can ask a question of the audience.

First imagine a simple unschema’d row:

Rob KloppDatabase Fog Bloghttp://robklopp.wordpress.com42

A human with some context could see that there is a name string, a title string, a URL string, and an integer string. If you have the right context you would recognize that the integer holds the answer to the question: “What is the meaning of Life, the Universe, and Everything?”… see here… otherwise you are lost as to the meaning.

If you load this row into a relational database you could leave the schema out and load a string of 57 characters… or load the data parsed into a schema with Name, Title, URL, Answer. If you load this row into a key-value pair you can load it into an unschema’d row with the Key = Row and the Value equal to the string… or parse the data into four key-value pairs.

In any case you have to parse the data… If you store the data in an unschema’d format you have to parse the data and bind value to keys to columns late… if you store the data parsed then this step is unnecessary. To bind the data late in SQL you might create a view from your program… or more likely you would name the values parsed with SQL string functions. To parse the data into key-value pairs you must do the equivalent. The same logic holds true for more complex parsing. A graph database can store keys, values, and relationships… but these facets have to be known and teased out of the data either early or late. An RDBMS can do the same.

So what is the benefit of a database product that proclaims late binding as an advantage? Is it that late binding is easier to do than in an RDBMS? What am I missing?

Please do not respond with a list of other features provided by NewSQL and NoSQL databases… I understand many of the trade-offs… what I want to know is:

  • What can they do connected to binding values to names that an RDBMS cannot? And if there is no new functionality…
  • Is there someway they allow for binding that is significantly easier?

By the way, the Hitchhiker’s Guide is silent on the question of whether 42 is a constant or ever-changing. I think that I’ll ask Watson.

Specialized Databases vs. Swiss Army Knives

Bowie Knife (500x206)(15884 bytes) - a typical...
“That’s not a knife… THAT’S A KNIFE” – C. Dundee (Photo credit: Wikipedia)

Michael Stonbreaker has suggested several times… and again in this interview… that  databases will become more specialized and that “one size will fit none”. I’m sure that his argument is more nuanced than the sound bites in the interview, but in this post I’ll suggest a line of thinking that may lead to a different conclusion.

First, let’s agree that the word “fit” means the best price for the performance required to meet your company’s service level requirements.

Then let’s agree with the basic premise behind Dr. Stonebreaker’s argument… we agree that in any single-purpose application a specialized single-purpose DBMS can be developed that will out perform a generalized DBMS. This means that one-half of the fit, performance, is likely.

We would also agree that between the growth of open source databases and the general growth in the database space that  it is likely that someone can and will develop specialized databases and bring them to market in cases where there is enough market to make it worthwhile. But it is important to note that specialization will be not become infinitely narrow… there has to be enough market for the special case to generate an attractive product.

So where is the disagreement: I do not believe that data is ever used in a single specialized business context. Not ever.

Let’s imagine that we have a business requirement for an extremely high volume OLTP application… and let us assume that the performance and/or scalability requirements are beyond what any general DBMS can provide and that the business ROI is significant… in other words, let us imagine that we are Google or Facebook. In this case we have no choice but to select or to develop an extreme, specialized, DBMS to solve the problem and extract the return.

But in this case, once the OLTP transactions are recorded… what do we do with the data? We need to use the data elsewhere in the business as the basis for deep analytics or for basic business intelligence… so we have to replicate the data to a second database. Since the second DBMS is also sort of specialized… it does not have to support OLTP… we select a second specialized, data warehousish product.

And then come new requirements for doing light queries in near real time to support operational analytics… so we build some sort of operational data store. Again we can select a product with a narrow technical sweet spot… but we have to replicate the data a third time.

In other words… given my premise… that data is never used in a single specialized context… specialized databases force replication… and replication allows for further specialization.

But what if the requirements are not so extreme? Then we might use a single conventional RDBMS for the EDW and for the ODS problems. If a more generalized DBMS product exists that could handle both the operational reporting and the analytic reporting requirements in a single image of the data then we could eliminate one replica and one DBMS. In other words, if the problem is not so extreme then a generalized solution might provide a solution in a single instance of the data avoiding replication.

Now the issue becomes: is the cost of a specialized system plus replication plus a second specialized system plus the cost of operating these systems less than the cost of a single generalized system? I believe that the answer will often be in favor of a single system even when the specialized systems are low-cost open source. Since “fit” is about cost maybe one size does fit now and again.

This suggests the strategy of the OldSQL vendors. They are offering a Swiss Army Knife product that serves multiple requirements. Their feature sets have grown over 30 years and they are pretty capable across a wide array of business problems… and with the columnar and in-memory features being added they continue to cover ever more extreme uses cases… not the most extreme use cases… but they cover more ground each year.

The strategy of the NewSQL vendors is to focus tight and hard. They might develop an extreme OLTP DBMS with no ability to do a join… a product with extreme scalability and no performance… or a graph database to solve for an important, narrow, set of queries… or a columnar product that performs analytics but support no OLTP. This trend feeds the specialize and replicate meme advocated by Dr. Stonebreaker.

HANA is a horse of a different color… neither NewSQL nor OldSQL. It is a new code base designed to solve for a very wide set of uses cases in a single instance of the data. We certainly agree in this blog with Dr. Stonebreaker’s contention that the 30 year old legacy code base has to be retired. But SAP contends that you can build a new, generalized, DBMS that solves for all but the most extreme cases.

This is a great spot to end the year… having laid out the battle we will cover in this blog ongoing… with the legacy OldSQL vendors trying to tack on to their legacy code base… and doing pretty well at it… with the NewSQL vendors trying to specialize and replicate… and with HANA offering a new code base designed to solve for the the whole picture. 2014 will be great fun to watch. This also sets the stage to ask next year whether “big data” applications are so extreme as to force users to specialize-replicate-specialize.

Have a great holiday season…  and my best wishes. Thank you all for reading the Database Fog Blog in 2013… I hope for your continued attention in the New Year…

– Rob

CPUs and HW for HANA, BLU, Hekaton, and Oracle 12c

CPUs from retired computers waiting for recycl...
(Photo credit: Wikipedia)

This short post is intended to provide a quick warning regarding in-memory columnar and cpu requirements… with a longer post to follow.

When a row is inserted or bulk-loaded into a DBMS, if there are no indexes, the amount of cpu required is very small. The majority of the time is spent committing a transaction is the time to write a log record to persist the data.

When the same record is reformatted into a column the amount of processing required is significantly higher. The data must be parsed into columns, the values must be compressed, dictionaries may be updated, and the breadcrumbs that let the columnar data be regenerated into rows must be laid. Further, if the columnar structure are to be optimized then the data must be ordered… with a sort or some kind of index structure. I have seen academic papers that suggest that for an insert columnar processing may be 100X more than row processing… and you can see why this could be true (I apologize for not finding the reference… I’ll dig it up… as I recall I read it in a post some time back by Daniel Abadi).

Now let’s think about this… several vendors are suggesting that you can deploy their columnar features with no changes required… no new hardware… in-place. But this does not ring true if the new columnar feature requires 100X extra CPU cycles per row… or 50X… or 10X… unless you are running your database on an empty server.

This claim is a shot at SAP who, more honestly, suggests new hardware with high-end processors for their in-memory columnar product… but methinks it is marketing, not architecture, from these other folks.

HANA Memory Utilization

The current release of HANA requires that all of the data required to satisfy a query be in-memory to run the query. Let’s think about what this means:

HANA compresses tables into bitmap vectors… and then compresses the vectors on write to reduce disk I/O. Disk I/O with HANA? Yup.

Once this formatting is complete all tables and partitions are persisted to disk… and if there are updates to the tables then logs are written to maintain ACIDity and at some interval, the changed data is persisted asynchronously as blocks to disk. When HANA cold starts no data is in-memory. There are options to pre-load data at start-up… but the default is to load data as it is used.

When the first query begins execution the data required to satisfy the query is moved into memory and decompressed into vectors. Note that the vector format is still highly compressed and the execution engine operates on this compressed vector data. Also, partition elimination occurs during this data move… so only the partitions required are loaded. The remaining data is on disk until required.

Let us imagine that after several queries all of the available memory is consumed… but there is still user data out-of-memory on peripheral storage… and a new query is submitted that requires this data. At this point HANA frees enough storage to satisfy the new query and processes it. Note that, in the usual DW case (write-once/read-many), the data flushed from memory does not need to be written back…  the data is already persisted… otherwise HANA will flush any unwritten changed blocks…

If a query is submitted that performs a cartesian product… or that requires all of the data in the warehouse at once… in other words where there is not enough memory to fit all of the vectors in memory even after flushing everything else out… the query fails. It is my understanding that this constraint will be fixed in a next release and data will stream into memory and be processed in-stream instead of in-whole. Note that in other databases a query that consumes all of the available memory may never complete, or will seriously affect all other running queries, or will lock the system… so the HANA approach is not all bad… but as noted there is room for improvement and the constraint is real.

This note should remove several silly arguments leveled by HANA’s competitors:

  • HANA, and most in-memory databases, offer full ACID-compliance. A system failure does not result in lost data.
  • HANA supports more data than will fit in-memory and it pages data in-and-out in a smart fashion based on utilization. It is not constrained to only data that fits in-memory.
  • HANA is not useless when it runs out of memory. HANA has a constraint when there is more data than memory… it does not crash the system… but lets be real… if you page data to disk and run out of disk you are in trouble… and we’ve all seen our DBMS‘s hit this wall. If you have an in-memory DBMS then you need to have enough memory to support your workload… if you have a DB2 system you better not run out of temp space or log space on disk… if you have Teradata you better not run out of spool space.

I apologize… there is no public reference I know of to support the features I described. It is available to HANA customers in the HANA Blue Book. It is my understanding that a public version of the Blue Book is being developed.

Who is How Columnar? Exadata, Teradata, and HANA – Part 1: Column Compression

Basic Table

There are three forms of columnar-orientation currently deployed by database systems today. Each builds upon the next. The simplest form uses column-orientation to provide better data compression. The next level of maturity stores columnar data in separate structures to support columnar projection. The most mature implementations support a columnar database engine that performs relational algebra on column-oriented data. Let me explain…

Imagine a simple table with 1M rows… with the schema and the first several rows depicted in Figure 1. Conceptually, a row-orientation deploys data on disk and in-memory as depicted in Figure 2 and a column-orientation deploys data on disk and in-memory as depicted in Figure 3. The actual deployment may be significantly different, as we will see.

Note that I am going to throw out some indicative numbers around compression. I will suggest that applying compression to rows will provide from 1.5X to 3.5X compression with and average of 2.5X… and that applying compression to columns provides from 3X compression to 50X compression with the average around 10X. These are supportable numbers but the compression you see for any specific data set will vary.

A row oriented block

There are two powerful compression techniques that individually or combined provide most of the benefits: dictionary-encoding and run-length encoding. For the purposes of this blog I will describe only dictionary-encoding; and I will do an injustice to that by explaining it only briefly and conceptually… just enough that you get the idea.

Five column oriented blocks

Further compression is possible by encoding runs of similar values to a value plus the number of times it repeats so that the bit stream 0000000000000000 could be represented as 01111 (0 occurs 24 times).

You can now also start to see why column-orientation compresses better that a row-orientation. In the row block above there is little opportunity to encode whole rows in a dictionary… the cardinality of rows in a table is too high (note that this may not be true for a dimension table which is, in-effect, a dictionary). There is some opportunity to encode the bit runs in a row… as noted, you can expect to get 2X-2.5X from row compression for a fact table. Column-orientation allows dictionary encoding to be applied effectively to low cardinality columns… and this accounts for the advantage there.

Col Dict

Dictionary-encoding reduces data to a compressed form by building a map that provides a translation for each cardinal value in the table to a tightly compressed form. For example, if there are indeed only three values possible in the DeptID field above then we might build a dictionary for that column as depicted in Figure 4. You can see… by encoding and storing the data in the minimal number of bits required, significant storage reduction is possible… and the lower the cardinality of a column the smaller the resulting bit representation.

Note that there is no free lunch here. There is a cost to be paid in CPU cycles to compress data and to decompress data… but for a read-optimized data warehouse database compression is cool. Exactly how cool depends on the level of maturity and we will get to that as we go.

It is crucial to remember that column store databases are relational. They ingest rows and emit rows and perform relational algebra in-between. So there has to be some magic that turns tuples into columns and restores them from columns. The integrity of a row has to persist. Again I am going to defer on the details and point you at the references below… but imagine that for each row a bit map is built that, for each column, points to the entry in the column dictionary with the proper value.

There is no free lunch to column store… no free lunch anywhere, it seems. Building this bit map on INSERT is very expensive, and modifying it on UPDATE is fairly expensive. This is why column-orientation is not suitable for OLTP workloads without some extra effort. But the cost is amortized by significant performance gains for READs.

One last concept: since peripheral I/O reads blocks imagine two approaches to column compression: one applies the concepts above to an entire table breaking each table into separate column-oriented files that may be read separately; and one which applies the concepts individually to each large block in a table file. Imagine, in the first case that Figure 2 represents a picture of the first few rows in our 1M-row table. Imagine, in the second case, that Figure 2 represents the rows in one block of data re-oriented into columns.

This second, block-oriented, approach is called PAX, and it is more-or-less the approach used by Exadata. In the PAX approach each block contains its own mini-column store and a dictionary for dictionary encoding with the values in the block. Because the cardinality for columns within a block will often be less than for an entire table there are some distinct advantages to PAX compression. Compression will be higher by more than a little than for full table columnar compression.

When Exadata reads a block from disk it decompresses the data back into rows and performs row-oriented processing to complete the query. This is very cool for Exadata… a great feature. As noted, column compression may be 4X better than row compression on the average. This reduces the storage requirements and reduces the overhead of I/O by 4X… and this is a very significant improvement. But Exadata stops here. It is not a columnar-oriented DBMS and it misses the significant advantages that come from the next two levels of column-orientation… I’ll take these up in the next post.

To be clear, all of the databases that use these more mature techniques: Teradata, HANA, Greenplum, Vertica, Paraccel, DB2, and SQL Server gain from columnar compression even if the PAX approach provides some small advantage as a compression technique.

It is also worth noting that Teradata does not gain as much as others in this regard. This is not because of poor design, rather it is due to the fact that, to their credit, Teradata implemented a Teradata-specific dictionary-based compression scheme long ago. Columnar compression let others catch up to what Teradata has offered for years.

And before you ask… Netezza offers no columnar orientation… preferring to compress deeply using an FPGA co-processor to decompress… and to reduce I/O using zone maps rather than the using the mid-level column projection techniques in the next blog here.

Indexes are not a good thing… A blog on TCO

In many of my posts I refer to the issues associated with building “extra” data structures to meet performance goals (see one of my first posts ever here). These extra structures are always a trade-off… slowing the performance of one function in order to speed up another. I thought that it might be helpful to be very clear about where I stand on this.

Indexes improve the performance of queries that address a small set of data. They also can improve join performance if your favorite optimizer can apply an index intersection to the execution plan for your queries. Indexes dramatically slow the performance of inserts, updates, and bulk data loads as they have to be maintained when data changes. You can mitigate the cost and update indexes in the background… the trade-off does not go away. Indexes are probably required for OLTP applications that pick out single rows.

Wouldn’t it be great if your favorite DBMS could resolve every query very fast without the overhead and operational effort associated with maintaining indexes? Certainly we should aspire to a read-optimized database, a data warehouse DBMS, that does not require indexes.

Vertica projections provide an optimized, materialized, view that improves the performance for a set of queries. The Vertica optimizer automatically selects the optimal projection. Vertica provides a very slick tool that builds projections based on the query set provided. I worded my post on Vertica a little vague… so let me be sure here to point out that  every Vertica query runs against a projection… so it is possible to have only one. In this case there is no additional overhead. Adding projections slows the data load process and increases the storage requirements. This is the trade-off.

Other databases offer materialized views. They make the same trade-off as above.

An OLAP cube is a physical structure that pre-aggregates data so that your query workload can avoid the aggregation. The best implementations of this express the cube as a materialized view so that queries can use the pre-aggregated data without explicitly pointing at a cube structure… the optimizer picks it for you. In addition the best implementations let you drill out of the cube to the detail records. These products have the update/delete/load issues of an index plus add an extra data latency issue as the data has to be aggregated on some interval… usually hours or days. Many products do not allow joins from a cube. You can see the trade-off. The Oracle Exalytics product materializes the aggregated cube on a separate server in-memory. This provides even more performance but adds the system and operational overhead of moving data across system boundaries.

Wouldn’t it be nice if you could query raw data and perform aggregation so fast that even against terabytes of data you could run any query with 3 second or less response without the overhead of building cubes?

You may build specialized table structures and pre-join, pre-aggregate, or pre-compute data to make a set of queries run fast. The cost of building and maintaining this sort of implementation versus just querying the base tables is the trade-off. Further, this approach is sort of a trap. You cannot build these structures for every query… if you did the business would conceive another critical query the next day that required work.

You can add indexes to the structures built using the technique above and provide very fast application-specific performance to a small set of queries. This is currently the favored approach when companies build iOS or Android apps as it provides the best possible performance… at a significant price.

Wouldn’t it be great if this was unnecessary… you could just scan so fast that mobile response service levels could be met from the base data regardless of the query.

You can deploy redundant data in operational data stores, data marts, cube servers, analytic data stores, and so on… with each specialized store providing performance for some limited set of queries at the cost of development and support ongoing. Each of these copies could deploy specialized database products that speed up that set of queries a little more. Again, this surround-the-EDW approach is a trap that leads to the proliferation of data marts and of database technologies.

Please do not take that last paragraph the wrong way… I believe that the worst possible approach is to blindly standardize on one or two database products. This trade-off makes life convenient for the IT department at the expense of performance and agility in the business. It is OK to have one or two favored products but IT must always serve the business to the best of their ability as a first priority… and sometime the new start-up has just the thing (remember that once Teradata was a start-up and DB2 on the mainframe was the IT standard…).

What I wish was that one or two products could solve all of the performance and functionality problems without the cost of building “extra” stuff… one product would be better that two. I like products that make the extra stuff “free”. Netezza does a nice job of making zone maps “free”, for example. Teradata and Greenplum provide the option of row store or column store for “free”. Vertica automatically build extra projections for “cheap”… and while there is a cost to the projection it at least does not require staff to tune it up. Oracle materialized views are “cheap”.

What I dislike are products that require DBAs to work harder and harder to apply all of the techniques above to meet performance SLAs. Each of these techniques trades off performance for development and operational expense.

As I have noted before… the performance SLAs for BI are about to become severe as companies try to support BI on mobile devices. The development and operational costs of tuning up; that is the TCO; will be significant unless better, faster, software infrastructure becomes available.

The TCO for a database that could eliminate these extra constructs and could eliminate the cost of developing and maintaining them; and could eliminate the architectural fragility these approaches imply… and replace this with a DBMS that holds base data which could satisfy all queries in seconds; delivering the business agility this implies… the TCO would be compelling.

I actually believe that the answer is available in the market today… this is no longer a pipe dream… more later…