Introduction

Let me explain my experience leading the whole Data Architecture (split by layers, see on my previous post here) and also leading and creating from zero the whole Enterprise Data Warehouse solution for my current company.

 

About the company

Avoiding names, I would like to introduce few facts about this company. It is one of the largest ecommerce companies in the world with more than 13,000 employees. This company has more than 70 active companies or services attached to its core company, providing a huge variety of business such as: Insurance, Telecommunication, bank, credit card, travel, sports (bought soccer club, beisbol club, etc),…

 

About the data

So for that, we have more than 500 databases distributed around the world with thousands and thousands of tables, as mentioned before, talking about very different business domains. Size of it, still unknown, but so far we have in our hands around 2PB (and growing).

 

How to implement Agile DW with DV2.0

 

First: Data ingestion (Bring all your data into your Data Lake and keep history records)

So in order to get all this data into our History Stage (copy of the original + history), we did developed a Python script and a MetaData Management to automate all the ingestion, but that’s another topic that I will cover in another post, here I am going to focus on the EDW solution to get as much as possible from all this data.

  

 

Second: prepare automation for your Data Vault 2.0

This is very important step as it will provide a huge benefit for a cheap price. Talking about my own experience, I created a whole framework in Python code that auto populates Hub, Satellite, Link and SameAsLink objects in about 2 weeks of Development.

How does it work? Easy! You just need to create a view that follows the Data Vault naming convention. Let’s say that we create a Satellite view to feed our DV, and it will automatically populate, not only a Satellite (table and load), but also Hubs reusing the same view (possibilities to automate are limitless). With a bit of code in our framework, our view will be able to:

  • * Create hub table (if not exists).
  • * Load hub information (only new data).
  • * Create Satellite table (if not exists)
  • * Drop and create views such as vw_[name]_current and vw_[name]_history.
  • * Load Satellite information (new, updated and deleted data).
  • * Get metadata and governance to know which Entities, DV Objects and business we are loading.

 

This is a sample of my naming convention for the framework:

[DV Object]_[Entity]_[Business]_[common/[others]] ==> sat_customer_bank_common

 

Third: split your Satellites using the flexibility of DV2.0

So, the beauty of Data Vault is its scalability and flexibility, which is perfect for complex scenarios such as developing an EDW with an initial unknown scope for a very big company. Since companies are so different from each other and we don’t know how many entities we will need at the end, we started creating some basic entities, such as: customer, order, orderdetail, product, item and so forth.

So we are also putting all the common attributes in a common Sat for each entity, because, even though Phone, a Bank or an eCommerce companies have almost nothing in common, they will still have customers and these customers will share common attributes such as Name, Address, DOB, Gender, etc. This is just finding semantical understanding to our data and using it.

For those attributes that are specific for each business, then we can just create a special satellite for customer banks (salary, rate, etc), other satellites for travel business (frequent flyer number, preferred destinations, etc).

That means, we don’t need to design the whole EDW in one goal, neither we need to include all the business of each entity in order to start getting value.

With the common attributes, we can reuse the same customer segmentation or KPI reports across each business or all together (or by groups) only with one report and a filter for the company/ies that we want to analyse.

What about Item, Order, Order detail, etc? Easy find the semantical understanding of the data. For example, in eCommerce item could be an ipad2, in bank could be loan package 30 years, in travel could be travel package, or even a hotel room (i.e.: “Holiday Inn – Atlanta – Double standard“) and so forth. So later you’ll be able to reuse the same report to check which item was the most successful during one period (agnostic of which kind of product it is).

NOTE: Of course, other good practice is to split your satellites by change rate, so the columns that change the most could be in one satellite and ETL it very often and the ones with low change/priority could be loaded daily or weekly etc.

 

Fourth: Supernova layer or “Business Delivery Layer” (c)

Thanks to our MetaDataManagement, we can automate creation of views removing the DV complexity. So, Business users can start looking at the EDW with a 3NF language that they are more comfortable or create (an even automate) our virtual Star Schemas, based on only views, so much easier to create, recreate and fine tune.
* BTW, I prefer to call it “Business Delivery Layer” .


 

Some references:

 

Pure (and real) Agile Data Warehouse

So the first and second steps are king of one off, once is developed and running in an automation way.

The third step is the one that can be done, one entity/business at the time and that means, because we are not aiming to deliver all of them at the same time. So we can apply agile sprints at target for a number of entities and business for this sprint (let’s say 2 weeks).

Once these new entities/business are in production, you can easily go to the fourth step and create the supernova of it (aim for automation when possible) and data consumers can start enjoying this part of the EDW, or at least, checking if they need something else, if they are missing things etc. So if that happens in the supernova layer, as they are all views, it will be very fast to fix it, if it is a major change in the DV layer, then next sprint we can fix it just creating new satellites (always adding/appending, never rebuilding or throwing away anything).

 


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So in order to expose the different layers and artefacts contained in this architecture see in the next picture and refer the numbers in the table below.

Data Architecture, Data Lake, Data Vault, Data Virtualization, Data governance and Data lineage

NumDescription
1Data source or Data Owners space. This could be Relational Database, API, Flat files, etc.
2Python customized script that will do all the ELT, capture audit information, feed the MDM (with Metadata automatically and configuration through operators) etc
3Layer where we will store all the data sets on its raw shape (just adding audit or ELT extra columns). Ideally it will be placed on Hive (Data Lake)
4When python (E)xtracts the source information into a file, then it loads it into Hadoop/Hive. This could be Delta or Full. This table is totally temporal, so it is not persistent.
5Now python will do the (L)oad. With our extra columns, we can hash the upcoming data and compare it through the Business Key to the one already stored in the History Stage (persistent) table. Then we will insert ONLY new and updated data. Later we will run a Delete Detection Pattern and insert the deleted Rows.
6This table is persistent and it will contain the initial full load and the inserted/deleted/updated new records on the following loads.
7The enterprise layer (or integration layer) is where our EDW will be located. Typically in Hive, but if needed could be stored anywhere else.
8Python will also load from our Raw Layer, the already modelled (through views ideally) data into a persistent EDW tables. In this case, we will apply only Hard Business Rules, which are the ones that not change the meaning of the data, just the shape. Example: Change data type, standardize Timestamps into a unique format, etc.
This data will land into what we called "Raw Data Vault". Modelled with DV 2.0 fashion, the data won't be agreegated or changed here.
9If required (optional) we will create out Business Data Vault, which could be views or another ELT to transform the data into more meaningful data for the business, where we will apply business rules, do aggregations, merge data, etc.
10This layer works on top of the DV layer. Because DV modelling is quite complex (even for some Data Engineers), this layer is meant to create (automatically if possible) a set of views with the information stored in RDV and BDV in a 3NF fashion (or even Star Schema fashion). So the Data consumers doesn't need to deal with the modelling complexity of DV2.0
11This Database with the output of EDW (DV) could be stored in Hive or Teradata or any other high performance database for later consumption. Ideally it will be just views or materialized views.
12This is our Data Virtualization space. From here we will choose a technology able to do cross platform queries and expose all our Raw Layer and EDW information through only this channel. Because the will connect to a simple JDBC or ODBC, they don't need to deal with the complexity of looking for data in Hive or in Teradata, etc. Everything will be simplified.
13We will apply Security and expose only the access level for that specific user (stored in MDM) creating views to the granted tables and columns. This database (in presto in our example) will need to regenerate all the views to follow the security specs stored in MDM or to capture new tables (also specified in MDM)
14Backbone of everything. Here we will stored the Metadata (refresh in every load), the patterns to use when loading, the extra configuration (blacklist columns/tables, identify delta fields) and also deal with the security to be exposed in the Presentation (or data Access layer)
15Audit database will track the data lineage of every single row and also stored information about the ELT and even, through presto, how many people are accessing which tables and how often. With this we can do a hot/warm/cold strategy.

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Basically, if you keep your history just exposing the datetime when the record was inserted or updated, it is possible to get a view of your table in the shape of a Slowly Change Dimension Type 2. The way to achieve it is to mention your LoadDateTime as StartDate and then create a partition over the business key to identify the next LoadDateTime, and if there is no more, expose year 9999 or 2100 (no end). The following code will explain that in a real scenario. Note: ignore the audit fields that I used to create in the History Staging Area, which I will explain in my next post.

CREATE VIEW [hstg].[vw_Table_History]
AS
SELECT
ETL_EXECUTION_DT AS START_DATE,
ISNULL(lead (ETL_EXECUTION_DT) OVER (PARTITION BY  BusinessKey ORDER BY ETL_EXECUTION_DT), ‘9999-12-31 00:00:00.0000000’) AS END_DATE,
CASE WHEN lead (ETL_EXECUTION_DT) OVER (PARTITION BY BusinessKey ORDER BY ETL_EXECUTION_DT) IS NULL THEN ‘Y’  ELSE ‘N’ END AS [CURRENT_RECORD],
[BusinessKey],
[Field1],
[Field2],

ETL_BATCH_DT AS ETL_ROW_START_DT,
S.ETL_BATCH_ROW_ID,
CONVERT (DATETIME, ‘99991231’) AS ETL_ROW_END_DT,
ETL_ROW_HASH,
CONVERT (NVARCHAR (512), ‘AdvWorks’) AS ETL_ROW_SOURCE,
ETL_CDC_OPERATION,
ETL_EXECUTION_DT
FROM [hstg].[Table] S


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Introduction

This is probably a key factor, technically speaking, of the future health of your BI solution. There is not perfect nor unique “Data Modelling” that will fit in ALL solutions, but there are some points that will power up your future DW and extend to the max. all the possibilities.

Data modeling it is so extensive concept that can’t be covered within one post neither one book, but we can provide some easy to understand “dos and don’ts” when creating your Staging Area and DW for reporting.

 

STAGING AREA

Prepare yourself for ANYTHING and get AS MUCH AS YOU CAN

This sentence is key if we are getting our data from the source to the staging area. Basically, we have to capture all the data from the source system, and keep record of the original modeling.

So it important to get all the Business Keys, Foreign Keys, nullable or non nullable fields attributes, etc. from the source system tables. And most important, record all the history at the same time. That means, every time we run our ETL, we need to bring all the data, and capture some audit columns in order to keep record of the history. So if at any point, there is a PK (or BK) that is changing in the source, we need to create another record in our Staging table with the CDC info, i.e.: INSERT/UPDATE/DELETE

That will create a database with the data as it is in the source system, adding some audit fields and history, so at any point in time we can recreate our DW using its history and we won’t miss anything out.

Dos:

  • * Raw data in Stage, respecting the DDL (datatypes, fields, etc.)
  • * Get any table that might be a potential for your interest. The DB space/resources are limited, so I won’t say get EVERY single tables no matter what, but if possible, that is not a bad idea.
  • * Keep history, so you can recreate your DW and Datamarts easily in the future.

Don’ts:

  • * Don’t change data, like computing or merging two fields (i.e.: name + surname = full name)
  • * Don’t crop or truncate any fields. If you thing a datatype of VARCHAR(2000) is too big, keep that length in your staging or even round it up to 4000 or MAX.
  • * Don’t start modeling or “fixing” the data model in your Staging Area, even if it looks wrong, you should respect this DDL at this stage, that is something you’ll start working on the next phase, while moving data to DW or even better, to your presentation layer.

 

DATA WAREHOUSE

For our Data Warehouse I can’t recommend a unique model, as every solution/business is different, and the purpose of this DW could be Archiving, reporting, build a base for OLAP/Tabular cubes and so on.

The most extended and well known models are:

 

3NF

Pro

  • save most storage of all modelling techniques
  • simple to understand

Con

  • bad performance with multiple joins
  • difficult to load (ETL)
  • changes are very difficult to handle

 

* Star Schema

Pro

  • Simple design
  • fast queries
  • fits very well to olap models
  • many DBMS are optimized for queries on star schemas

Con

  • usually centralized on one fact table
  • higher storage usage due to denormalization

 

My suggestion is, to use “Data Vault” http://en.wikipedia.org/wiki/Data_Vault_Modeling in the DW core and from that point you can build star schemas in data marts. To explain the benefits of DV would take more than 1 post, so if you are really interested, just Google it or have a look at the Wikipedia link I provided.

Cheers!

 

 


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The purpose of this post is to clarify some basics on the SSAS Tabular Cubes and how we can apply Incremental updates in order to achieve RealTime and its best practice.

 

First of all it is important to know about the basic processing options on Tabular cubes:

 

Object Available Processing Options
Database Process Clear, Process Default, Process Defrag, Process Full, Process Recalc
Table Process Clear, Process Data, Process Default, Process Defrag, Process Full
Partition Process Add, Process Clear, Process Data, Process Default, Process Full

 

And the meaning of these processing options:

 

Processing Option Description
Process Add Adds new rows to a partition. Any affected calculated columns, relationships, user hierarchies, or internal engine structures (except table dictionaries) are recalculated.
Process Clear Drops all the data in a database, table, or partition.
Process Data Loads data into a partition or table.
Process Default Loads data into unprocessed partitions or tables. Any affected calculated columns, relationships, user hierarchies, or internal engine structures (except table dictionaries) are recalculated.
Process Defrag Optimizes the table dictionary (an internal engine structure) for a given table or for all tables in the database*. This operation removes all dictionary entries that no longer exist in the data set and rebuilds the partition data based on the new dictionaries.
Process Full Loads data into all selected partitions or tables. Any affected calculated columns, relationships, user hierarchies, or internal engine structures (except table dictionaries) are recalculated.
Process Recalc For all tables in the database, recalculates calculated columns,  rebuilds relationships. rebuilds user hierarchies, and rebuilds other internal engine structures. Table dictionaries are not affected.

 

Once we have a clear idea of all the options we can apply in our BI Lifecycle we must differentiate between the concept that update or refresh your database doesn’t mean real update DWH:

 

  • Recalculate (Process Recalc) is not going to add new info, it is going just to recalculate all the measures even if you don’t insert new data in your cube.

 

  • Partitioning is a very common and old practice used mainly in the big solutions (huge amount of rows) where you need to process some old part of your BI solution only once and that’s not going to change. i.e.: sales 2005, 2004, 2003… In order to define your partitions you are flexible enough to specify a query that will bring only part of the table to these partitions, like “WHERE ID_Dim_Date >= 20010101 and ID_Dim_Date <= 20021231” where your current partition will have something like “WHERE ID_Dim_Date > 20130101” . That could be an option to only process part of your data, but it is not the best practice because you have to define your partitions which they’ll be at the Year or Month level, that means, if you have to re-process your 2013-11 partition every 5 minutes to aim realtime data.

 

  • Incremental processing (Process Add) is the one to achieve your beloved real-time. It will do the deltas by itself, adding or updating whatever just changed. Sadly, you can’t specify a query to apply the deltas only for an specific period.

 

Best Practice:

The ideal scenario is to use the process Add but not using the whole table (reducing the amount of data to process). Hence we can use a Partition, let’s say for 2013-11 and on top of that, ProcessAdd, which will keep and process very quickly the deltas. Then you can re process the cube as many times as you need and getting closer to what we call “real time”.


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