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Apache Drill: Compilation WorkshopJacques Nadeau, OSCON July 23, 2013

jacques@apache.org |@intjesus

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Runtime Compilation is Faster

JIT is smart but more gains can be had with runtime compilation

From http://bit.ly/16Xk32x

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How do you do runtime compilation?

Runtime Compilation Tools javax.tools.Compiler (since 1.6): Wrapper to compile string into

bytecode using javac Janino: New BSD licensed Java-based Java compiler

Which One? Simple benchmarks shows Janino performs substantially faster

than javax.tools.Compiler Janino doesn’t support Annotations nor Generics (ugh.)

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Code Play Time

Get Latest Drill git clone git://git.apache.org/incubator-drill.git git checkout master cd incubator-drill/sandbox/prototype mvn install

Download OSCON Drill examples git clone https://github.com/jacques-n/oscon-drill.git

cd oscon-drill mvn install cd compile

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Exercise 1: Runtime Compilation Example

Goal Generate and evaluate your first runtime compiled code leveraging

Janino

Overview Janino provides a simple ExpressionEvaluator interface– Takes array of Objects as parameters– Returns single Object that can be casted to appropriate output class

Simplest way to use ExpressionEvaluator is by using a variable holder class– Variables in the exercise

Code src/test/java/org/apache/drill/oscon/compile/E1JaninoTest.java

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Conclusions

Runtime compilation is easy Managing and building strings is painful Object interface is less than elegant

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Simplification is necessary

CodeModel to the rescue– CodeModel provides a simplified interface for programmatically generating

Java source code– Extremely expressive, supporting all major constructs– Apache Licensed (yay!)

Use interfaces to manage things– Define an interface– Generate an entire class instead of just an evaluation block– Ensure class implements interface then generate new instance of runtime

generated class

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Exercise 2: CodeModel + Interfaces

Goal Clean up the previous implementation to make it more repeatable

Overview JCodeModel provides interface to generate new class JExpr, JFieldVar, JMethod and other classes used via invocations or

statically Use Drill’s QueryClassLoader to help inject bytecode into

Classloader

Code src/test/java/org/apache/drill/oscon/compile/E2CodeModelTest.java

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Conclusions

Things are better…but– Large blocks of code are going to be painful to do with CodeModel

Isn’t there some way to merge compile time generated code with runtime generated code?

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Solution: Runtime Bytecode Merging

CodeModel to generate runtime specific blocks Janino to generate runtime bytecode Precompiled bytecode templates Use ASM package to merge the two distinct classes into one

runtime class

Loaded ClassASM Bytecode Merging

Janino compilation

CodeModel Generated

Code

Precompiled Bytecode Templates

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Exercise 3: Template Merging Approach

Goal Leverage best of generated and pre-compiled world

Overview Drill’s ClassTransformer class does the dirty work, taking a TemplateDefinition

and InternalInterface source code ClassTransformer also marks class final and all methods private final except

external ones to maximize likelihood of JVM inlining. Drill’s QueryClassLoader is again used

Code src/test/java/org/apache/drill/oscon/compile/E3TemplateMergeTest.java src/main/java/org/apache/drill/oscon/compile/InsideInterface.java src/main/java/org/apache/drill/oscon/compile/OutsideInterface.java src/main/java/org/apache/drill/oscon/compile/OutsideTemplate.java

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Exercise 4: Drill example

Goal– Apply generalized knowledge to Drill

Overview– Drill utilizes a combination of templating and code generation to build

query level operators– We also use source code rewriting to simplify implementation of scalar

functions– To minimize function overhead, all scalar function evaluations are merged

into large evaluation blocks.– FunctionDefintion and DrillFunc combine to provide implementation– drill-module.conf is used to inform Drill of available extension

Code– src/main/java/org/apache/drill/oscon/compile/AbsoluteFunction.java– src/test/java/org/apache/drill/oscon/compile/E4AbsTest.java

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Drill Implementation: Expression Compilation

Best of all worlds: Runtime Bytecode Merging Balance development effort and performance needs Interpretation overhead during record batch setup Compile time operation for large code blocks