Pentaho Review

Pentaho BI Suite Review: PDI – Part 1 of 6


Introduction

The Pentaho BI Suite is one of the more comprehensive BI suite that is also available as an Open Source project (the Community Edition). Interestingly, the absence of license fees is far from being the only factor in choosing this particular tool to build your Data Warehouses (OLAP systems).

This is the first of a six-part review of the BI suite. In each part of the review, we will take a look at the components that make up the BI suite, according to how they would be used in the real world.

In this first part, we'll be discussing the Pentaho Data Integration (from here on will be referred to as PDI) which is the ETL tool that comes with the suite. An ETL tool is the means with which you input data from various sources – typically out of some transactional systems, then transform the format and flow into another data model that is OLAP-friendly. Therefore it acts as the gateway into using the other parts of the BI suite.

In the case of PDI, it has two components:

  • Spoon (the GUI), where you string together a set of Steps within a Transformation and optionally string multiple Transformations within a single Job. This is where you would spend the bulk of your time developing ETL scripts.

  • The accompanying set of command-line scripts that we can configure to be launched from a scheduler like cron or Windows Task Scheduler. Notably pan a single Transformation runner, kitchen the Job runner, and carte the slave-server runner. These tools give us the flexibility to create our own network of multi-tiered notification system, should we need to.

Is it Feature-Complete'

ETL tools are interesting because anyone who has implemented a BI system have a standard list of major features expected to be available. This standard list does not change from one tool brand to the other. Let's see how PDI fares:

  1. Serialized vs Parallel ETL processing: PDI handles parallel (async.) steps using Transformations, which can be strung together in a Job when we need a serialized sequences.

  2. Parameter-handling: PDI has a property file that allows us to parameterize things that are specific to different platforms (dev/test/prod) such as database name, credentials, external servers. It also features parameters that can be created during the ETL run out of the data in the stream, then passed on from one Transformation to another within a Job.

  3. Script management: Just like any other IT documents (or as some call it artifacts), ETL scripts need to be managed, version-controlled, and documented. PDI scores high on this front. Not because of some specific features, instead, due to design decisions that favor simplicity: The scripts are plain XML documents. That makes it very easy to manage, version-control, and if necessary batch-edit. NOTE: For those who wants enterprise level script management and version-control built into the tool, Pentaho made it available as part of their Enterprise offerings. But for the rest of us who already have a document management process – because we also develop software using other tools – it is not as crucial.

  4. Clustering: PDI supports round-robin -style load-balancing given a set of slave-servers. For those using Hadoop clusters, Pentaho recently added their support to run Jobs on those.

Is it Easy to Use'

With the drag and drop graphical UI approach, the ease of use is a given. It is quite easy to string together steps to accomplish the ETL process. The trick is knowing which steps to use, and when to use it.

The documentation on how to use each step can stand improvements that fortunately, slowly over the years have started to catch up – and should you have the budget, you can always pay for support that comes with the Enterprise Edition. But overall, it is a matter of using those enough to be familiar with the use cases.

This is why competent BI consultants are worth their weights in gold because they have been in the trenches, and have accumulated ways to deal with the quirks which is bound to be encountered in a software system this complex (not just Pentaho, this applies to any BI Suite products out there).



NOTE: I feel obligated to point out one (very) annoying fact that I cannot hit the Enter key to edit the selected step. Think about how many times we would use this functionality on any ETL tool.

Aside from that, in the few years that I've used various versions of the GUI, I've never encountered severe data loss due to stability problems.

Another measurement of ease-of-use that I evaluate a tool with is: How easy it is to debug the ETL scripts. With PDI, the logical structures of the scripts could be easily followed, therefore it's quite debug-friendly.

Is it Extensible'

It may be a strange question at first, but let us think about it. One of the purpose of using an ETL tool is to deal with a variety of data sources. No matter how comprehensive the included data format readers/writers, sooner or later you would have to talk to a proprietary system that is not widely-known. We had to do this once for one of our clients. We ended up writing a custom PDI step that communicates with the XML-RPC backend of an ERP system.

The good news is, with PDI, anyone with some Java SDK development experience, can readily implement the published interfaces and thus creating their own custom Transformation steps. In this regard, I am quite impressed with the modular design, that allows users to extend the functionality and consequently, the usefulness of the tool.

The scripting ability built into the Steps is also one of the ways to handle proprietary – or extremely complex data. PDI allows us to write Javascript (and Java, should you want faster performance) programs to manipulate the data both at the row level as well as pre- and post- run, which comes very handy to handle variable initializations or sending notifications that contain statistical info about all of the rows.

Summary

The PDI, is one of the jewels in the Pentaho BI Suite. Aside from some minor inconveniences within the GUI tool, the simplicity, extensibility, and stability of the whole package makes PDI a good tool for building a network of ETLs marshaling data from one end of the systems to another. In some cases, it even serves well as a development tool for the batch-processing side of an OLTP system.

Next in part-two, we will discuss the Pentaho BI Server.

Disclosure: I am a real user, and this review is based on my own experience and opinions.
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