8 ms·
It's really easy to get lost in the technical jargon that the vendors who are selling products throw around, but this article has missed the important part, and
by wokwokwok 3y ago
It's really easy to get lost in the technical jargon that the vendors who are selling products throw around, but this article has missed the important part, and spent all the time talking about the relatively unimportant part (data formats).
You need to step back and look from a broader perspective to understand this domain.
Talking about arrow/parquet/iceberg is like talking about InnoDB vs MyISAM when you're talking about databases; yes, those are technically storage engines for mysql/mariadb, but no, you probably do not care about them until you need them, and you most certainly do not care about them when you want to understand what a relational DB vs. an no-SQL db are.
They are technical details.
...
So, if you step back, what you need to read about is STAR SCHEMAS. Here are some links (1), (2).
This is what people used to be before data lakes.
So the tldr: you have a big database which contains condensed and annotated versions of your data, which is easy to query, and structured in a way that is suitable for visualization tools such as PowerBI, Tableau, MicroStrategy (ugh, but people do use it), etc. to use.
This means you can generate reports and insights from your data.
Great.
...the problem is that generating this structured data from absolutely massive amounts of unstructured data involves a truly colossal amount of engineering work; and it's never realtime.
That's because the process of turning raw data into a star schema was traditionally done via ETL tools that were slow and terrible. 'Were'. These tools are still slow and terrible.
Basically, the output you get is very valuable, but getting it is very difficult, very expensive and both of those problems scale as the data size scales.
So...
Datalakes.
Datalakes are the solution to this problem; you don't transform the data. You just injest it and store it, basically raw, and on the fly when you need the data for something, you can process it.
The idea was something like a dependency graph; what if, instead of processing all your data every day/hour/whatever, you defined what data you needed, and then when you need it, you rebuild just that part of the database.
Certainly you don't get the nice star schema, but... you can handle a lot of data, and what you need to do process it 'adhoc' is pretty trivial mostly, so you don't need a huge engineering effort to support it; you just need some smart table formats, a lot of storage and on-demand compute.
...Great?
No. Totally rubbish.
Turn out this is a stupid idea, and what you get is a lot of data you can't get any insights from.
So, along come the 'nextgen' batch of BI companies like databricks so they invent this idea of a 'lake house' (3), (4).
What is it? Take a wild guess. I'll give you a hint: having no tables was a stupid idea.
Yes! Correct, they've invented a layer that sits on top of a data lake that presents a 'virtual database' with ACID transactions that you then build a star schema in/on.
Since the underlying implementation is (magic here, etc. etc. technical details) this approach supports output in the form we originally had (structured data suitable for analytics tools), but it has some nice features like streaming, etc. that make it capable of handling very large volumes of data; but it's not a 'real' database, so it does have some limitations which are difficult to resolve (like security and RBAC).
...
Of course, the promise, that you just pour all your data in and 'magic!' you have insights, is still just as much nonsense as it ever was.
If you use any of these tools now, you'll see that they require you to transform your data; usually as some kind of batch process.
If you closed your eyes and said "ETL?", you'd win a cookie.
All a 'lake house' is, is a traditional BI data warehouse built on a different type of database.
Almost without exception, everything else is marketing fluff.
* exception: kafka and streaming is actually fundamentally different for real time aggregated metrics, but its also fabulously difficult to do well, so most people still don't, as far as I'm aware.
...and I'll go out on a limb here and say really, you probably do not care if your implementation uses delta tables or iceberg; that's an implementation detail.
I guarantee that correctly understanding your domain data and modelling a form of it suitable for reporting and insights is more important and more valuable than what storage engine you use.
[1] - https://learn.microsoft.com/en-us/power-bi/guidance/star-schema https://learn.microsoft.com/en-us/power-bi/guidance/star-sch...
[2] - https://www.kimballgroup.com/data-warehouse-business-intelligence-resources/books/data-warehouse-dw-toolkit/ https://www.kimballgroup.com/data-warehouse-business-intelli...
[3] - https://www.snowflake.com/guides/what-data-lakehouse https://www.snowflake.com/guides/what-data-lakehouse
[4] - https://www.databricks.com/glossary/data-lakehouse https://www.databricks.com/glossary/data-lakehouse
- xvector 3y agoAs someone that came away confused after reading the article, this was hugely helpful - thanks.
- krysp 3y agoAll very good and useful points. One additional thing to mention is that as you are querying across the raw data with a data lake(house), performance is fundamentally worse, even if a lot of the marketing material will tell you otherwise. Usually significantly worse than if your data was in a columnar database in practice. Depending on your use case this may or may not be a problem. For most companies I'd wager that it is a bigger problem than it first appears.
- jamesblonde 3y agoAll of this is correct, but it misses the main point of the new table formats - they are open-source and the data can be stored on very low cost storgae - S3. So, having a data warehouse that stores TBs or even PBs of data is not as expensive as it used to be (by an order of magnitude or more). And the formats for storing the data (Parquet), its metadata (Iceberg, Hudi, delta lake), its query engine (DuckDB, Polars, Ibis) - they are all open-source.
- wokwokwok 3y ago> it misses the main point of the new table formats I didn't miss it; it's irrelevant. It makes, almost no difference in practice, between a competent implementation in one and a competent implementation in the other. It makes absolutely no difference that they are open source. Understanding the details of each of the individual components will give you no meaningful insight into how to build a lakehouse. ...because, when you slap all those parts together, in whatever configuration you've picked what you end up with is a database. A big, powerful cloud database. Well, you have a database now and you still have zero insights and zero idea how to get any of them; that because you didn't understand that you need to build some kind of data warehouse on top of that database. You need to load the data. You need to transform the data. You need to visualize the data and build reports on it. If you're good, you probably need to preprocess the data to use as training inputs. I'll say it more clearly and explicitly one. more. time: - Having a database != having a data warehouse. - Having a big cloud database build out of cloud storage, table formats, metadata engines and query engines != a lakehouse. Having an empty database is of no value to anyone, no matter how good it is. All of those parts, all of those things are only the first step. It's like installing postgres. Right, good job. We're done here? Reports? Oh, you can probably import something or something or I know, powerBI is good, let's install that. It'll tell you you have no data... but... we've got the infra now right? Basically done. It's just step 1.