qStudio 1.43 Released. This:
Download it now.
kdb+ 3.5 had a significant number of changes:
The feature that most interests us right now is the Debugging functionality. If you are not familiar with how basic errors, exceptions and stack movement is handled in kdb see our first article on kdb debugging here. In this short post we will only look at the new stack trace functionality.
Now when you run a function that causes an error at the terminal you will get the stack trace. Here’s a simple example where the function f fails:
Whatever depth the error occurs at we get the full depth stack trace, showing every function that was called to get there using .Q.bt[]:
The good news is that this same functionality is availabe in qStudio 1.43. Give it a try: qStudio.
Note: the ability to show stack traces relies on qStudio wrapping every query you send to the server with its own code to perform some analysis and return those values. By default wrapping is on as seen in preferences. If you are accessing a kdb server ran by someone else you may have to turn wrapping off as that server may limit which queries are allowed. Unfortunately stack tracing those queries won’t be easily possible.
That’s just the basics, there are other new exposed functions and variables, such as .Q.trp – for trapping calls and accessing traces that we are going to look at in more detail in future.
qUnit has added a new HTML report to allow visually easily seeing the difference between expected kdb results and actual results. To generate a report you could call:
.qunit.generateReport[.qunit.runTests[]; `:html/qunit.html]
It’s also added a
.qunit.assertKnown[actualResult; expectedFilename; msg]
call to allow comparing an actual results to a file on disk. While allow easy updating of that file and avoiding naming collisions.
This post is a walkthrough of my implementation in Q of the RosettaCode task ‘Death Star’.
The code is organized as general-purpose bitmap generator which can be used in other projects, and a client specific to the task of deathstar-drawing. The interface is a function which passes a map of pixel position to pixel value. The map can be a mapping function, or alternatively a 2D array of pixel values. The bitmap generator raster-scans the image, getting pixel values from either a mapping function or a mapped array.
genheader follows directly from the referenced BMP Wikipedia article.
genbitmap and genrow perform a raster scan of the image to be constructed. genbitmap steps along the vertical axis, calling genrow, which steps along the pixels of the current line, in turn calling fcn, the pixel-mapping function passed in by the client.
A sample client is included in comments, the simplest possible demonstration of shape and color (a circular mask selecting between two fill colors):
Conveniently, functions and arrays can be equivalently accessed in Q.
Here is an array-passing client which replicates the first example in the Wikipedia article on BMP format.
Element ordering can be confusing at first glance: Byte order for RGB pixels is B,G,R. Also, rows are indexed from bottom to top, and since bitmaps are in row-major order, the first and second array indices designated x and y correspond to the y and x image axes respectively.
After centering the image fcn applies several masks:
is calculates the orientation of a point on a sphere, and then a pixel value for that point, using the dot product of l, the light source direction, and s, the surface orientation. A correction of (1+value)/2 is applied, to achieve the ‘soft’ appearance of a space object in a movie. Alternatively we might have suppressed negative illumination values, to get the high-contrast appearance of an actual space object.
We might want to generate images of the death star at different rotations, however due to some simplifying assumptions we can’t rotate the weapon face to the side without glitching. We calculate z1 and z2 to select between the forward surface of the death star and the rearward surface of the weapon face. We should also calculate z3, the forward surface of the weapon face sphere, and z4, the rearward surface of the death star:
z3:170+z[x2;y;r];
z4:-z1;
Then the masks can be modified so that when z3 > z1 > z4 > z2, an additional bit of background is visible through the carved-out chunk of the deathstar.
TODO: discuss limitations of mask-and-fill; alternative approaches; display-list; …
TODO: discuss animation; …
TODO: discuss three-component architecture: orchestrator, world, bitmap generator
TODO: … conclusions
qStudio 1.41 is now available to download.
It adds the ability to use custom Security Authentications and custom JDBC drivers.
By automatically loading .jar plugins from libs folder.
After a few users reported issues around “watched expressions” we are removing the ctrl+w shortcut as it was often getting used by mistake. The last change was some internal work to improved startup/shutdown logging for debugging purposes..
Recently there was a post on SQL tips by the JOOQ guys. I love their work but I think standard SQL is not the solution to many of these problems. What we need is something new or in this case old, that is built for such queries. What do I mean, well let’s look through their examples reimplemented in qsql and I’ll show you how much shorter and simpler this could be.
In kdb we take this a step further and make tables standard variables, no special notation/treatment, it’s a variable like any other variable in your programming language. Instead of messing about with value()() we define a concise notation to define our variables like so:
This is the example syntax they have used to define two tables and then join them:
What to hell! If I want variables, let’s have proper variables NOT “Common Table Expressions”.
I created two tables a and b then I joined them sideways. See how simple that was.
Oh dear SQL how badly you have chosen your examples. Running calculations are to APL/qSQL as singing is to Tom Jones, we do it everyday all day and we like it. In fact the example doesn’t even give the full code. See this SO post for how these things get implemented. e.g. Standard SQL Running Sum
qSQL table Definition and Running Sum:
This is their code:
This is KDB:
In 1974 Ken Iverson gave a talk on APL. He described how he reduced it down to a core set of operations that everything could be made from. Using these simple building blocks you could make some really cool things. It’s sad to think we may not have came that far.
qSQL/kdb is a database based on the concept of ordered lists, carrying over many ideas from APL that make array operations shorter and simpler. If you like what you see we provide tutorials on kdb to get started, this intro is a good place to get started.
We also have free online kdb training for students.
First, in case you haven’t heard about it kdb has a standard SQL mode, you can send queries prefixed with s) and they will be interpreted as standard SQL like so:
Notice how the standard “and” syntax worked when I used s) but without it, q’s right to left evaluation causes problems. It’s about now that a lot of people get very excited, they think great I can skip learning that q-sql and use my standard SQL. Sometimes the look of joy on their faces transforms to frustration once they start using it. So let’s look at what works:
| Operation | Works? |
|---|---|
| Standard SQL Inserts | Yes |
| ORDER BY | half works |
| COUNT | Yes |
| DELETE | Yes |
| UPDATE | Yes |
| String matching | slightly works |
| NOT | NO |
| IN | Yes |
| GROUP BY | Yes |
| LIMIT / TOP | NO |
| Date Times | NO |
“ORDER BY” will sort the columns in ascending order, attempting to use DESC has no effect.
Modifying our String query slightly by adding NOT throws an error. My guess is that the interpreter has got confused.
Overall standard SQL support in kdb has got much better. However I would still recommend only using the s) syntax for plugging into an existing jdbc/odbc visualization tool and getting some immediate simple results. For any form of complex queries on strings, joins etc. support is either not there or the result may not be what you expect.
qStudio 1.40 is now available to download.
The latest changes include:
Previously on our blog we had a lively debate about a possibly Open Sourced kdb+ , unfortunately kx now seems to be moving the opposite direction. In a recent announcement they are now restricting “32-bit kdb+ for non-commercial use only”. The timing is particularly unfortunate as:
Alternative (far less enterprise proven) solutions are available:
This renewed interest in kdb alternatives hasn’t so far delivered a kdb+ killer but I fear in time it will.
An intellij keyword file is now available to provide syntax highlighting of kdb code in intellij:
q Code Intellij Highlighting
To install it copy this xml file to this directory:
C:\Users\USERNAME\.IdeaIC14\config\filetypes
Where USERNAME is obviously your username. Then restart intellij and open a .q file.
We’ve updated our notepad++ qlang.xml to provide code folding and highlighting of the .Q/.z namespaces.