Skip to main content

Evaluating Exadata… Does it stack up with RDBMS-Hadoop systems? Part 2

In my earlier blog  I suggested that we could evaluate RDBMS-Hadoop integration architecture using three criteria:
  1. How parallel are the pipes to move data between the RDBMS and the parallel file system;
  2. Is there intelligence to push down predicates; and
  3. Is there more intelligence to push down joins and other relational operators?
But Exadata is a split RDBMS with a parallel file system backing it… how does it measure up by these criteria?
There are effective parallel pipes between the Oracle RAC RDBMS and the Exadata Storage Subsystem… so Exadata passes the first test. Further, Exadata is smart about pushing scan and projection both down to the Storage layer.
Unfortunately there is a fairly severe imbalance between the number of nodes on the RAC side and the number of nodes on the Storage side and this creates a bottleneck. We cannot give Exadata full marks here… but as far as parallel pipes goes it stacks up pretty well.
The ability to push down predicates goes a long way towards solving this as the predicate push-down reduces the amount of data that has to move over the bottleneck. But in every data warehouse there will be queries that return lots of rows from the early execution steps… and Exadata cannot join data in the Storage Subsystem so it tries to pull data up sparingly and push down semi-joins whenever possible… it just cannot be done in every case (Note: in Exadata POCs Oracle will try to ensure that no queries are included that pull lots of data up to the RAC layer… and competitors will try to include queries that expose this weakness…).
So… Oracle also includes some intelligence to push some data down to reduce data movement. There is no way to choose to move data from the RAC layer to the Storage Subsystem and execute the query there… the Storage Subsystem can only scan and project… so again we cannot give Exadata full marks… but it is pretty smart as you will see when we start looking at alternative implementations.
Finally, Exadata cannot effectively split a single query plan across both layers… so no marks at all here.
So Exadata is pretty good… but it has weak spots that will be severe for an important set of DW queries in any implementation.

Comments

Post a Comment

Popular posts from this blog

Python and Parquet Performance

In Pandas, PyArrow, fastparquet, AWS Data Wrangler, PySpark and Dask. This post outlines how to use all common Python libraries to read and write Parquet format while taking advantage of  columnar storage ,  columnar compression  and  data partitioning . Used together, these three optimizations can dramatically accelerate I/O for your Python applications compared to CSV, JSON, HDF or other row-based formats. Parquet makes applications possible that are simply impossible using a text format like JSON or CSV. Introduction I have recently gotten more familiar with how to work with  Parquet  datasets across the six major tools used to read and write from Parquet in the Python ecosystem:  Pandas ,  PyArrow ,  fastparquet ,  AWS Data Wrangler ,  PySpark  and  Dask . My work of late in algorithmic trading involves switching between these tools a lot and as I said I often mix up the APIs. I use Pandas and PyArrow for in-RAM comput...
Post a Comment
Read more

Ingesting IoT Sensor Data Into S3 With an RPI3

StreamSets Data Collector Edge is a lightweight agent used to create end-to-end data flow pipelines. We'll use it help stream data collected from a sensor. Due to the increasing amount of data produced from outside source systems, enterprises are facing difficulties in reading, collecting, and ingesting data into a desired, central database system. An edge pipeline runs on an edge device with limited resources, receives data from another pipeline or reads the data from the device, and controls the device based on the data. StreamSets Data Collector (SDC) Edge, an ultra-lightweight agent, is used to create end-to-end data flow pipelines in StreamSets Data Collector and to run the pipelines to read and export data in and out of systems. In this blog, StreamSets Data Collector Edge is used to read data from an air pressure sensor (BMP180) from an IoT device (Raspberry Pi3). Meanwhile, StreamSets Data Collector is used to load the data into Amazon's Simple Storage Service ...
Post a Comment
Read more

Real-Time Talk: Windows 10 IoT Core Background Tasks and ASP.NET Core Web Apps

Display useful information from your Windows 10 IoT Core application in an ASP.NET Core web app, essential for integrating IoT data into a solution. Windows 10 IoT background task talk with a web application using WebSockets. Problems As my path to this solution has been troublesome, I am listing here the main problems I faced so my dear readers have a better idea of dead-end streets along the way: I was not able to make the ASP.NET Core web application run under a Windows 10 IoT background service. I found no information about when or if it will be supported in the near future. ASP.NET MVC and ASP.NET Core have different SignalR implementations. I was not able to make a SignalR client for .NET Core work with SignalR hosted on a web application. I was able to make things work by directly using a WebSocket. It’s not as nice a solution as I had in my mind, but it works until things get better. Making the Background Task and Web Application Talk I worked out sim...
Post a Comment
Read more