QStudio
Query kdb+ Servers and Chart Results.
Timing a kdb Query
Often I get asked:
- How can I time how long to run a query?
- Does kdb have a profiler?
- How can I tell which query is faster?
Timing a Query
First let's create a table t.
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q)n:1200300
q)t:([] a:til n; s:n?`3; ex:n?4?`3; size:n?100; price:n?1000.)
q)t
a s ex size price
-----------------------0 ddd ifb 37 537.5576
To time how long a query takes to run we could use the system t or \t command.
Running a command prefixed with \t causes it to return the time that it took to run in milliseconds.
We can then go one step further and use the \t:n command to run the same query n times and return the total time in milliseconds.
As shown below:
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q)select from t where s=`ddd
a s ex size price
---------------------------0 ddd ifb 37 537.5576
443 ddd ifb 37 383.565
1154 ddd peg 12 385.8024
Finding the memory required for a Query
If we want to profile both how much time and how much memory a query takes to run we can use \ts:n.
This returns two values, the time taken in milliseconds and the space required in bytes.
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q)\ts select from t where s=`ddd
4 2101600
q)\ts:100 select from t where s=`ddd
298 2101536
One area that we have used this is as part of the qunit test framework for kdb, we log how much memory and time a test takes to run. The framework also allows specifying the maximum time/memory that a unit test should take.
Another interesting idea to try is automatically breaking functions into statements and timing each part, or creating a tool that profiles each line. QStudio provides a basic version of this:
