Using materialized view to create a different sort order of the base table can reduce cost substantially, in this example up to 200 X for some queries.
The Problem : You can’t have multiple sort order.
One of most effective technique in columnar database to improve speed is to sort the table which will help the engine scan less data, but what if you have some queries that works better with different sorting, obviously you can’t have independent column sorted in the same table , turn out BigQuery has a very nice functionality, Materialized views which are used mainly to aggregate Data, see example here, can also works fine without aggregation and you can even change the sort order of the base table.
Example using PowerBI
In this report, which show analyze Electricity production for the Australian Market, the base table is sorted by day, that make perfect sense as most uses will want to see only a specific time period then aggregate by some attribute like region, technology etc
The Model is very simple , a fact table in Direct Query mode, and two dimensions in Import mode, a very simple star schema
The main report is a couple of charts using some aggregation, nothing particularly interesting, the queries use the Materialized view as we are aggregating per day, the base table is by minutes.
Drill Down to details
The trouble start here, let’s say a user want to see all the data for one particular Station name to the lowest level of details.
The Engine will have to scan the full table, as the table was sorted by date not by Station name
as you can see 4.61 GB is a lot of data scanned just to see one station name.
Non Aggregation Materialized View
let’s create a new MV with a different sort order, notice there is no group by, it is the same number of rows as the base table and you can’t have different partitions, only sort can be changed.
create materialized view `XXX_MV_Sort`
cluster by DUID,DAY as
SELECT
*
FROM
BASE_Table
The Same Query is substantially cheaper 🙂 from 4.6 GB to 19 MB, that’s 230 times cheaper.
you can see the two Query Plan, one scanning 101 Millions rows vs 404000 rows
Take away
Because BigQuery already knows about all the queries, it may be useful to have some kind of service that give suggestions, like changing sort or adding a Materialized view, in the meantime, I think Modeling still matter and can save you a lot of money.
in a previous blog, I did benchmark some database using TPCH-SF100, one of the main complaint was that the data was originally from snowflake although I did rewrite the parquet files using DuckDB, it did not feel right as Snowflake performance using the lowest tier was exceptionally good, in this blog, I am using Data generated independently, and yes Snowflake is very fast.
Reproducibility
Since that blog, DuckDB released a new update where you can generate any TPCH data using low resource computer (like my laptop), I thought it is a good opportunity to validate the previous results, this time though, I published the full pipeline so, it can be reproduced independently.
Import the data from Azure Storage to Snowflake native table using create table as select from external table, the import took around 10 minutes ( that was rather slow to be honest), the data is imported as it is, no sorting, and no table distribution shenanigans.
I did noticed Snowflake has a better compression ratio than Parquet, for example the table “lineitem” size in Parquet is 25 GB, in Snowflake file format is 13.8 GB
Run TPCH benchmarks 2 times then do it again 1 hour later (I wanted to be sure that the disk cache was expired) obviously keeping the result cache off
The Results
Run 1 and 3 are querying data directly from Azure Storage you can see that from the local disk cache in Query 1, subsequent Queries use the data cached in the local SSD, notice the cache is temporary, if you suspend your Compute, you may lose it, Although Snowflake tries to give you back the same VM if available.
I plotted the results in PowerBI using the Query history table, The numbers are impressive, I think it is the combination of excellent features working together, great compression, extreme pruning, great Query plan, exact statistics, the whole thing make an extremely efficient engine.
Take away
Database performance is a very complex subject and vary based on the workload, but I wanted to have a simple heuristic, a number that I can reference, I think I have that magic Number 🙂 if your Database can Run TPCH-SF100 around 2 minutes and cost you around 2 $, you can say it is fast.
Saw a linkedin post where someone used my previous test for TPCH-SF10 and added Tableau Hyper Engine to the mix, the number were too good, that’s something that make me suspicious, I do like average results, extremes may just means a glitch or just a random good run, I had to see it for myself, and what a wonderful discovery, yes Hyper is extremely fast.
What is Hyper
Hyper is a DB originally developed in a german university and bought by Tableau in 2016 to replace their calculation engine, it is a full feature relational Database that support SQL, and not a specialized DB like PowerBI Vertipaq or Qlik Engine.
To be honest, I knew about Hyper before, The API was released in 2020but I was very annoyed by a weird functionality where you need to double quote tables name and columns name, I was not too excited by the idea of apply this to a 900 LOC of SQL, luckily Romain was very kind and shared the modified SQ.
Edit : turn out double quote is not needed, probably the documentation was confusing, or I got the wrong impression.
To be clear Hyper Engine Package for Python is totally standalone and does not require Tableau, just PIP install tableauhyperapi , it is free to use but with proprietary license.
The Free Colab Test
I like using the free colab notebook to test Execution Engine (DuckDB,Data fusion, Polars etc) how an Engine behave in a constrained environment will give you a lot of useful intuition, and if it does not work well with limited resources, you will end up paying more in hardware cost because of software inefficiency, Design decisions matter.
TPCH-SF10
I started with the easy test, SF10, that’s 60 Million rows, Hyper performed nealy 2X faster than DuckDB, you can explained that Hyper had more time to mature compared to DuckDB, which is I think is only 3 years Old.
It may sounds weird, but I really wanted to see an Engine finish the SF30 (180 Million rows)using the free colab notebook, it became like a personal obsession, DuckDB and Data fusion could not finish it as they got Out of memory error, and Hyper just run, it was not even trying hard.
For no rational reason, I thought, let’s push the maximum and see what happen, the main table is 660 Million rows, in a free colab, and yes it was very slow, but did not crash and completed the test, that’s awesome !!
First let’s have a look at the file size, I had to delete the Parquet files to after loading just to save on the disk space.
That’s 47 GB, the Free Colab VM has only 13 GB of RAM, an Engine like PowerBI Vertipaq would not work, as it needs first to load the whole file into RAM, before running any Queries, Hyper works differently, it stream the data straight from the disk, and will just read what’s required by the Query using only the column needs and the rows needed, basically it is extremely efficient at prunning data from the disk.
Now let’s see the second graph
I was watching the RAM usage and it is absolutely beautiful, most of the time it is less than 2 GB, in some Queries you can see the memory usage increase then Hyper decide to spill to disk, I was very worried about Query 21 ( The DB killer) and Hyper just smash it, like it is nothing, it was so efficient, you can nearly feel the engine, everything make sense, it was a joyful moment.
Some Observation
This is just my personal opinion having played with a couple of SQL Engine.
You don’t need a specialist DB to handle Analytical Workload, a well designed columnar DB like Hyper and others is the perfect example.
I love DuckDB, but there is still a lot of work to do, which is a good news, as we can still squeeze more juice from our laptops.
I always believed PowerBI vertipaq to be the golden standard of analytical DB, I am not sure anymore, loading everything to RAM regardless of the Queries received seems a bit archaic these days, streaming from disk with only what’s required seems a better use of the hardware, and it scale better.
I believe having a fast non trivial logical semantic layer that just generate SQL Queries to a DB maybe the right architecture for this era.
(Disclaimer : I use BigQuery for a personal project and it is virtually free for smaller workload, at work we use SQL Server as a Data Store, I will try my best to be objective )
TL:DR ;
Run TPCH-SF100 benchmark (base table 600 million rows) to understand how different Engine Behave in this workload using just the lowest tier offering, you can download the results here
Introduction
Was playing with Snowflake free trial ( maybe for the fifth time) and for no apparent reason, I just run Queries on TPCH-S100 Dataset, usually I am interested in smaller dataset, but I thought how Snowflake may behave with bigger data using the smallest cluster, long story short, I got 102 second, posted it in Linkedin and a common reaction was Snowflake is somehow cheating.
Obviously I did not buy the cheating explanation , as it is too risky and Databricks will make it international news.
Load the Data Again
Ideally I would have generated the Data myself and load it into Snowflake, generating 600 Million records in my laptop is not trivial, my tool of choice, DuckDB has an utility for that but it is currently single threaded, instead
I exported the data from Snowflake to Azure Storage as parquet files
Download it to my Laptop, generate new files using DuckDB as in Snowflake you can’t control the minimum size of files, you can control the max but not the Min
Snowflake Parquet External Table
My Plan was to run Queries directly on Parquet hosted on azure storage, the experience was not great at all, Snowflake got Query 5 join order wrong
Snowflake Internal Table
I loaded the parquet files generated by duckdb, Snowflake getting extremely good results. what I learnt, whatever Snowflake magic is doing, it is related to their proprietary file format.
BigQuery External Table
I have no frame of reference for this kind of workload, so I loaded the the data to BigQuery using external table in Google Cloud, Google got 5 minutes, one Run, 2.5 $ !!!!
BigQuery Internal Table
Loaded Data to BigQuery internal format, notice, BigQuery don’t charge for this operation , 2 Minutes 16 second, 1 Cold Run.
BigQuery Standard Edition
BigQuery added new pricing model where you pay by second, after the first minutes, I used the Standard Edition with a small size, I run the same query two time, unfortunately the new distributed disk cache don’t seems to be working, same result 5 minutes, that’s was disappointing
Redshift Serverless
Imported the same Parquet files into Redshift serverless, The schema was defined without Distribution keys, The results are for 3 Runs, the first run was a bit slower as it is fetching the data from the managed storage to the compute SSD the other 2 runs are substantially faster, I thought it is fair to have an average, Using the lowest Tier 8 RPU (2.88 $/Hour)
Redshift Serverless hot run was maybe the fastest performance I have seen so far, but they need still to improve on their cold Run.
I was surprised by the system overall performance, from my reading, it seems AWS basically rewrite the whole thing including separating compute from storage, Overall I think it is a good DWH.
Trino
Trino did not run Query 15, had to run a modified syntax but same results, 1 Run from Cold Storage, I am using the excellent service from Starburst Data
Synapse Serverless
Honestly, I was quite surprised by the performance of synapse serverless, initially I tested with the smaller file size generated by Snowflake and it did work, the first run failed but the second works just fine, I did like it, it did failed quickly, notice that Synapse run statistics on parquet files, so you would expect a more stable performance, not the fastest, but rather resilient.
Anyway , it took from 8-11 minutes, to be clear that’s not Synapse from two years ago.
Not related to the benchmark but I did enjoyed the lake database experience
Databricks External Table
I had not a great experience with Databricks, I could not simply pass authentication to Databricks SQL, you need a service principal and registering an App, and the documentation keep talking about Unity, which is not installed by default, This is a new install why Unity is not embedded if it is such a big deal ?
Anyway, First I created an external Table in databricks using the excellent passthrough technique in the Single Node Cluster, Databricks got 12 minutes,
Databricks Delta table
let’s try again with Delta, I created a new managed table, run optimize and analyse , (I always thought delta has already the stats), but it didn’t seems to make a big difference, still around 11 minutes, and this running from the disk, so no network bottleneck
DuckDB
My Plan was to run DuckDB on Azure ML, but I need a bigger VM than the one provided by default, I could not find a way to increase my Quota , I know it sounds silly, and I am just relating my experience, turn out Azure ML VM Quota is different from Azure VM, it did drive me crazy why I could get any VM in Databricks but Azure ML keep complaining I don’t have enough CPU.
Unfortunately I hit two bugs, first the native DuckDB file format seems to generate double the size of Parquet, the dev was very quick to identify the issue, the workaround is to define the table schema and then load the data using insert, the file became 24 GB compared to the original 40GB parquet files.
I End Up going with parquet files, I was not really excited by loading a 24 GB file in a storage account.
I run the Queries in Azure Databricks VM E8ds_v4 (8 cores and 64 GM of RAM)
As I am using fsspec with disk cache, the remote storage is used only the first run, after 4 tries, Query 21 keep crashing the VM 😦
Tableau Hyper
Tableau hyper was one of the biggest surprise, unfortunately, I hit a bug with Query 18, otherwise, it would have being the cheapest option.
Some Observations
Initially I was worried I made a mistake in Snowflake results, the numbers are just impressive for a single node tier, one explanation is the Execution Engine is mostly operating on compressed data with little materialization , but whatever they are doing, it has to do with the internal table format, which bring a whole discussion of performance vs openness, personally in a BI scenarios, I want the best performance possible, and wonder if they can get the same speed using Apache Iceberg.
Synapse Serverless improved a lot from last year, it did work well regardless of the data size of individual parquet files that I throw at it, and in my short testing it was faster than databricks and you pay by data scanned, so strictly speaking pure speed is not such a big deal but without a free result cache like BigQuery, it is still a hard sell.
Azure ML Quota policy was very confusing to me, and honestly I don’t want to deal with support ticket.
Databricks; may well be the fastest to run 100 TB, but for 100 GB workload, color me unimpressed.
DuckDB is impressive for an open source project that did not even reach version 1. I am sure those issues will be fixed soon.
Everything I heard about Redshift from twitter was wrong, it is a very good DWH, with Excellent performance.
BigQuery as I expected has excellent performance both for parquet and the native table format, The challenge is to keep the same using the new auto scale offering. added Auto scale performance, I think Google should do better.
Summary Results
You can find the results here, if you are a vendor and you don’t like the results feel free to host a TPCH-SF100 dataset in your service and let people test it themselves.
Note : Using SQL Query History : Bigquery one Cold Run , Synapse Serverless , Redshift Serverless and Snowflake a mix of cold and warm
(Note : Synapse Serverless always read from remote storage)
Databricks I am showing the best run from Disk, there is no system table, so I had to copy paste the results from the console.
Pricing
I did not kept the durations for Data load, it is just the cost for Read, obviously it is a theoretical exercise, and does not reflect real life usage which depends on other factors like concurrency performance , how you can share a pool of resources to multiple departement,free results cache, the performance of your ODBC drivers etc.
it is extremely important to understand what’s included in the basic price, for example.
Results cache:
BigQuery, Snowflake, Redshift results cache are free and you don’t need a running cluster, in Databricks you pay for it, Synapse don’t offer result cache at all.
Data loading :
BigQuery data loading is a free operation and other service like sorting and partitioning, in other DB you needs to pay.
Egress Fees :
Snowflake/BigQuery offer free egress fees, Other vendors you may pay, you need to check
Note :
BigQuery : for This workload make more sense to pay by compute not data scanned, either using auto scale, reserved pricing etc, I will try to test Auto scaling later.
Snowflake : I used the standard edition of Snowflake
Edit : I used a Google Colab notebook with a bigger VM for Hyper and DuckDB, see full reproducible notebook
Final Thoughts
Cloud DWH are amazing tech and only competition can drive innovation, not FUD and dishonesty, regardless of what platform you use, keep an eye on what other vendors are doing, and test using your own workload, you may be surprised by what you find.
Project Controls blog 