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Chapter 15. Compiler Reference

15.1. Introduction
15.2. Concepts
15.2.1. Module
15.2.2. EPL-objects
15.2.3. Dependencies
15.2.4. Dependency Resolution
15.2.5. Access Modifiers
15.2.6. Bus Modifier for Event Types
15.3. Compiling a Module
15.4. Reading and Writing a Compiled Module
15.5. Reading Module Content
15.6. Compiler Arguments
15.6.1. Compiler Configuration
15.6.2. Compiler Path
15.6.3. Compiler Options
15.7. Statement Object Model
15.7.1. Building an Object Model
15.7.2. Building Expressions
15.7.3. Building a Pattern Statement
15.7.4. Building a Select Statement
15.7.5. Building a Create-Variable and On-Set Statement
15.7.6. Building Create-Window, On-Delete and On-Select Statements
15.8. Substitution Parameters
15.9. OSGi, Class Loader, Class-For-Name
15.10. Authoring Tools
15.11. Testing Tools
15.12. Debugging
15.12.1. @Audit Annotation
15.13. Ordering Multiple Modules
15.14. Logging
15.15. Debugging Generated Code
15.16. Compiler Version and Runtime Version
15.17. Generated Code Optimizations

15.1. Introduction

The compiler provides the following functions:

The most important function of the compiler is to produce byte code for your module. Deploy the byte code into a runtime for execution.

The compiler interface is EPCompiler in package com.espertech.esper.compiler.client. You application obtains a compiler instance by calling the getCompiler method of EPCompilerProvider.

For example: 

EPCompiler epCompiler = EPCompilerProvider.getCompiler();

Use the compiler as follows:

15.2. Concepts

A module contains zero, one or multiple statements. A module is a source code unit as the compiler turns a module into byte code. A module does not need to be a text - a module can also be an object model.

In module text, statements appear separated by the semicolon (;) character. If there is a single statement in the module the semicolon can be left off.

The synopsis of a module file is: 

[module module_name;]
	[uses module_name; | import import_name;] [uses module_name; | import import_name;] [...]
	[epl_statement;] [epl_statement;] [...]

Use the module keyword followed a module_name identifier or a package (identifiers separated by dots) to declare the name of the module. The module name declaration must be at the beginning of the file, comments and whitespace excluded. The module name serves to check uses-dependences of other modules.

If a module file requires certain constructs that may be shared by other modules, such as named windows, tables, variables, event types, variant streams or inserted-into streams required by statements, a module file may specify dependent modules with the uses keyword. This servers to avoid name conflicts and automatic deployment can use this information to determine deployment order.

If the statements in the module require Java classes such as for underlying events or user-defined functions, use the import keyword followed by the fully-qualified class name or package name in the format package.*. The uses and import keywords are optional and must occur after the module declaration.

Following the optional deployment instructions are any number of epl_statement statements that are separated by semicolon (;).

The following is a sample module file explained in detail thereafter: 

// Declare the name for the module (optional).
module org.myorganization.switchmonitor;

// Declare other module(s) that this module depends on (optional).
// This can be used to resolve name conflicts.
uses org.myorganization.common;

// Import any Java/.NET classes of the given package name (optional). 
// Imports only handle classpath and do not import other modules.
import org.myorganization.events.*;

// Declare an event type based on a Java class in the package that was imported as above
create schema MySwitchEvent as MySwitchEventPOJO;

// Sample statement
@Name('Off-On-Detector')
insert into MyOffOnStream
select * from pattern[every-distinct(id) a=MySwitchEvent(status='off') 
  -> b=MySwitchEvent(id=a.id, status='on')];

// Sample statement
@Name('Count-Switched-On')
@Description('Count per switch id of the number of Off-to-On switches in the last 1 hour')
select id, count(*) from MyOffOnStream#time(1 hour) group by id;

The example above declares a module name of org.myorganization.switchmonitor. The example demonstrates the import keyword to make a package name known to the compiler for resolving classpath items, as the example assumes that MySwitchEventPOJO is a POJO event class. In addition the example module contains two statements separated by semicolon characters.

The following types of EPL-objects are managed by the compiler and runtime:

Your application can pre-configure event types and variables in a Configuration object.

A module can create any number of EPL-objects.

A module can depend on EPL-objects that are pre-configured or other modules created.

A module usually depends on event types and may also depend on other EPL-objects such as named windows or tables, for example. The compiler resolves all dependencies at compile-time. It produces byte code based on the information associated with the EPL-object. Upon deploying a compiled module's byte code into the runtime the runtime validates that dependencies exist.

For example, consider the following module: 

select accountId, amount from Withdrawal

The module above depends on the event type Withdrawal. The compiler resolves the event type name to an EventType instance. It produces code according to the event type. At time of deployment of the compiled module the runtime verifies that the Withdrawal event type exists.

Specifically, the compiler generates code like this:

Note

The compiler only tracks dependencies on EPL-objects.

The compiler does not track classpath dependencies. The runtime does not validate classpath dependencies.

The runtime validates that EPL-object dependencies exist before deploying a compiled module.

The runtime does not validate that the information about the EPL-object is the same as at compile-time.

In other words, the runtime does not validate that event property names, event property types, table column names and types, variable types, index property names and other compile-time information matches the information that was provided at compile time.

The compiler resolves an EPL-object by its name by looking at:

The term path encompasses the EPL-objects other modules define. The term local encompasses the EPL-objects the same module defines.

Coming back to the previous example: 

select accountId, amount from Withdrawal

The compiler finds an event type by name Withdrawal by:

In case the name cannot be resolved the compilation fails.

In case the name is found multiple times, the compiler checks as follows:

Access level modifiers determine whether other modules can use a particular EPL-object.

An EPL-object may be declared with the modifier public, in which case that EPL-object is visible to all other modules.

An EPL-object may be declared with the modifier protected, in which case that EPL-object is visible to other modules that have the same module name.

An EPL-object may be declared with the modifier private (the default), in which case that EPL-object is not visible to other modules.

Your application may set access modifiers by:

The following module declares a public named window to hold the last 10 seconds of withdrawal events: 

@public create window WithdrawalWindow#time(10) as Withdrawal

For event types there is a bus modifier that determines whether or not the event type is available for use with the sendEventType methods of the EPEventService runtime event service.

An event type may be declared with the bus modifier, in which case calls to sendEventType process the event.

An event type may be declared with the non-bus modifier (the default), in which case calls to sendEventType cause an exception to be thrown.

To understand this better, here is what sendEventType of EPEventService does: When your application calls any of the sendEventBean, sendEventMap, sendEventObjectArray, sendEventXMLDOM or sendEventAvro methods of EPEventService, the runtime finds the event type using the event type name that is passed. It associates the event type to the event object for processing the given event. If the event type name is not recognized or the event type does not have the bus modifier it throws an exception.

The bus modifier is not required for pre-configured event types. The bus modifier requires public access.

Your application may set the bus modifier by:

The following module declares a public event type that allows an application to send in events of that name: 

@public @buseventtype create schema AccountQueryEvent (accountId string)

The information herein pertains to the routeEventType and EventSender as well.

15.3. Compiling a Module

The compile method takes two parameters. The first parameter is the module text or an module object model. The second parameter are compiler arguments.

The output of the compiler is an EPCompiled instance. You can deploy EPCompiled instances directly into a runtime as described in Section 16.4, “Deploying and Undeploying Using EPDeploymentService”.

15.4. Reading and Writing a Compiled Module

The EPCompiledIOUtil class is a utility for writing and reading EPCompiled instances to and from jar-files:

15.5. Reading Module Content

Read and parse module files using the readModule and parseModule methods, which return a Module instance to represent the module information.

This code snippet demonstrates reading and parsing a module given a file name: 

Module module = EPCompilerProvider.getCompiler().read(new File("switchmonitor.epl"));

15.6. Compiler Arguments

The compiler arguments are:

Pass a Configuration instance to the compiler to configure the compiler. By default the compiler uses an empty configuration object.

The compiler only uses the common section and the compiler section of the configuration. The compiler ignores the runtime section of the configuration.

It is not necessary to pass a configuration object or to pre-configure event types. You may create event types by means of create schema.

A pre-configured event types is a convenience since the event type is already defined and ready to use. The common section of the configuration holds the pre-configured event types. The following sample adds a pre-configured WithdrawalEvent map-based event type: 

Map<String, Object> columns = new LinkedHashMap<>();
columns.put("accountId", String.class);
columns.put("amount", double.class);

Configuration configuration = new Configuration();
configuration.getCommon().addEventType("WithdrawalEvent", columns);
CompilerArguments args = new CompilerArguments(configuration);

To obtain a configuration object from a runtime call getConfigurationDeepCopy on EPRuntime: 

Configuration configuration = epRuntime.getConfigurationDeepCopy();
CompilerArguments args = new CompilerArguments(configuration);

More information on the common and compiler configuration can be found at Chapter 17, Configuration.

By default the compiler does not generate code for subscribers and the setSubscriber method on EPStatement throws an exception.

You may set the allowSubscriber option: 

Configuration configuration = new Configuration();
configuration.getCompiler().getByteCode().setAllowSubscriber(true);
CompilerArguments args = new CompilerArguments(configuration);

The compiler path provides EPL-objects that other modules may declare and that the current module may use.

For example, assume a module M1 that declares a named window WithdrawalWindow: 

@public create window WithdrawalWindow#time(10) as Withdrawal

A second module M2 may query the named window like so: 

select (select count(*) from WithdrawalWindow) as cnt from Withdrawal

Module M2 depends on the EPL-object WithdrawalWindow (a named window) that module M1 declares.

You can build a path from:

Assume that your application compiled module M1 like so: 

Map<String, Object> columns = new LinkedHashMap<>();
columns.put("accountId", String.class);
columns.put("amount", double.class);

Configuration configuration = new Configuration();
configuration.getCommon().addEventType("WithdrawalEvent", columns);

CompilerArguments arguments = new CompilerArguments(configuration);
EPCompiled compiledModuleM1 = EPCompilerProvider.getCompiler().compile("@public create window WithdrawalWindow#time(10) as Withdrawal", arguments);

The compiledModuleM1 instance holds the byte code of module M1.

After deploying compiled modules to a runtime, the compiler can build the path from the runtime.

The getRuntimePath method of EPRuntime returns the path object for use by the compiler. The path object is an instance of EPCompilerPathable.

The add method of CompilerPath accepts a EPCompilerPathable instance provided by a runtime.

For example, as follows: 

Map<String, Object> columns = new LinkedHashMap<>();
columns.put("accountId", String.class);
columns.put("amount", double.class);

Configuration configuration = new Configuration();
configuration.getCommon().addEventType("WithdrawalEvent", columns);

// Get a runtime
EPRuntime runtime = EPRuntimeProvider.getDefaultRuntime(configuration);
runtime.getDeploymentService().deploy(compiledModuleM1);

// Compile another module
CompilerArguments arguments = new CompilerArguments(configuration);
arguments.getPath().add(runtime.getRuntimePath());
EPCompiled compiledModuleM2 = EPCompilerProvider.getCompiler().compile("select (select count(*) from WithdrawalWindow) as cnt from Withdrawal", arguments);

Use the addPath method of CompilerPath to add a compiled module to path.

For example, as follows: 

CompilerArguments arguments = new CompilerArguments(configuration);
arguments.getPath().add(compiledModuleM1);
EPCompiled compiledModuleM2 = EPCompilerProvider.getCompiler().compile("select (select count(*) from WithdrawalWindow) as cnt from Withdrawal", arguments);

Compiler options provide compiler callbacks and other compile-time parameters:

Please consult the JavaDoc for more information.

15.7. Statement Object Model

The statement object model is a set of classes that provide an object-oriented representation of statement. The object model classes are found in package com.espertech.esper.common.client.soda. An instance of EPStatementObjectModel represents a statement's object model.

The statement object model classes are a full and complete specification of a statement. All EPL constructs including expressions and sub-queries are available in the statement object model.

The statement object model provides the means to building, changing or interrogating statements beyond the string representation. The object graph of the statement object model is fully navigable for easy querying by code, and is also serializable allowing applications to persist or transport statements in object form, when required.

The statement object model supports full round-trip from object model to statement string and back to object model: A statement object model can be rendered into a string representation via the toEPL method on EPStatementObjectModel. Further, the compiler API allows compiling a statement string into an object model representation via the eplToModel method on EPCompiler.

The statement object model is fully mutable. Mutating any list such as returned by getChildren(), for example, is acceptable and supported.

The following limitations apply:

  • Statement object model classes are not safe for sharing between threads other than for read access.

  • Between versions the serialized form of the object model is subject to change. There are no guarantees that the serialized object model of one version will be fully compatible with the serialized object model generated by another version. Please consider this issue when storing object models in persistent store.

A EPStatementObjectModel consists of an object graph representing all possible clauses that can be part of a statement.

Among all clauses, the SelectClause and FromClause objects are required clauses that must be present, in order to define what to select and where to select from.

Table 15.1. Required Statement Object Model Instances

ClassDescription
EPStatementObjectModelAll statement clauses for a statement, such as the select-clause and the from-clause, are specified within the object graph of an instance of this class
SelectClauseA list of the selection properties or expressions, or a wildcard
FromClauseA list of one or more streams; A stream can be a filter-based, a pattern-based, SQL-based and other; Add data windows here.

Part of the statement object model package are convenient builder classes that make it easy to build a new object model or change an existing object model. The SelectClause and FromClause are such builder classes and provide convenient create methods.

Within the from-clause you have a choice of different streams to select on. The FilterStream class represents a stream that is filled by events of a certain type and that pass an optional filter expression.

We can use the classes introduced above to create a simple statement object model: 

EPStatementObjectModel model = new EPStatementObjectModel();
model.setSelectClause(SelectClause.createWildcard());
model.setFromClause(FromClause.create(FilterStream.create("ReadyEvent")));

The model as above is equivalent to: 

select * from ReadyEvent

Notes on usage:

  • Variable names can simply be treated as property names.

  • When selecting from named windows or tables, the name of the named window or table is the event type name for use in FilterStream instances or patterns.

  • To compile an arbitrary sub-expression text into an Expression object representation, simply add the expression text to a where clause, compile the EPL string into an object model via the eplToModel method on EPCompiler, and obtain the compiled where from the EPStatementObjectModel via the getWhereClause method.

The EPStatementObjectModel includes an optional where-clause. The where-clause is a filter expression that the runtime applies to events in one or more streams. The key interface for all expressions is the Expression interface.

The Expressions class provides a convenient way of obtaining Expression instances for all possible expressions. Please consult the JavaDoc for detailed method information. The next example discusses sample where-clause expressions.

Use the Expressions class as a service for creating expression instances, and add additional expressions via the add method that most expressions provide.

The next example adds a simple where-clause to the EPL as shown earlier: 

select * from ReadyEvent where line=8

And the code to add a where-clause to the object model is below. 

model.setWhereClause(Expressions.eq("line", 8));

The following example considers a more complex where-clause. Assume you need to build an expression using logical-and and logical-or: 

select * from ReadyEvent 
where (line=8) or (line=10 and age<5)

The code for building such a where-clause by means of the object model classes is: 

model.setWhereClause(Expressions.or()
  .add(Expressions.eq("line", 8))
  .add(Expressions.and()
      .add(Expressions.eq("line", 10))
      .add(Expressions.lt("age", 5))
  ));

The Patterns class is a factory for building pattern expressions. It provides convenient methods to create all pattern expressions of the pattern language.

Patterns in EPL are seen as a stream of events that consist of patterns matches. The PatternStream class represents a stream of pattern matches and contains a pattern expression within.

For instance, consider the following pattern statement. 

select * from pattern [every a=MyAEvent and not b=MyBEvent]

The next code snippet outlines how to use the statement object model and specifically the Patterns class to create a statement object model that is equivalent to the pattern statement above. 

EPStatementObjectModel model = new EPStatementObjectModel();
model.setSelectClause(SelectClause.createWildcard());
PatternExpr pattern = Patterns.and()
  .add(Patterns.everyFilter("MyAEvent", "a"))
  .add(Patterns.notFilter("MyBEvent", "b"));
model.setFromClause(FromClause.create(PatternStream.create(pattern)));

This section builds a complete example statement and includes all optional clauses in one statement, to demonstrate the object model API.

A sample statement: 

insert into ReadyStreamAvg(line, avgAge) 
select line, avg(age) as avgAge 
from ReadyEvent(line in (1, 8, 10))#time(10) as RE
where RE.waverId != null
group by line 
having avg(age) < 0
output every 10.0 seconds 
order by line

Finally, this code snippet builds the above statement from scratch: 

EPStatementObjectModel model = new EPStatementObjectModel();
model.setInsertInto(InsertIntoClause.create("ReadyStreamAvg", "line", "avgAge"));
model.setSelectClause(SelectClause.create()
    .add("line")
    .add(Expressions.avg("age"), "avgAge"));
Filter filter = Filter.create("ReadyEvent", Expressions.in("line", 1, 8, 10));
model.setFromClause(FromClause.create(
    FilterStream.create(filter, "RE").addView("win", "time", 10)));
model.setWhereClause(Expressions.isNotNull("RE.waverId"));
model.setGroupByClause(GroupByClause.create("line"));
model.setHavingClause(Expressions.lt(Expressions.avg("age"), Expressions.constant(0)));
model.setOutputLimitClause(OutputLimitClause.create(OutputLimitSelector.DEFAULT, Expressions.timePeriod(null, null, null, 10.0, null)));
model.setOrderByClause(OrderByClause.create("line"));

This sample statement creates a variable: 

create variable integer var_output_rate = 10

The code to build the above statement using the object model: 

EPStatementObjectModel model = new EPStatementObjectModel();
model.setCreateVariable(CreateVariableClause.create("integer", "var_output_rate", 10));

A second statement sets the variable to a new value: 

on NewValueEvent set var_output_rate = new_rate

The code to build the above statement using the object model: 

EPStatementObjectModel model = new EPStatementObjectModel();
model.setOnExpr(OnClause.createOnSet("var_output_rate", Expressions.property("new_rate")));
model.setFromClause(FromClause.create(FilterStream.create("NewValueEvent")));

This sample statement creates a named window: 

create window OrdersTimeWindow#time(30 sec) as select symbol as sym, volume as vol, price from OrderEvent

The is the code that builds the create-window statement as above: 

EPStatementObjectModel model = new EPStatementObjectModel();
model.setCreateWindow(CreateWindowClause.create("OrdersTimeWindow").addView("win", "time", 30));
model.setSelectClause(SelectClause.create()
		.addWithName("symbol", "sym")
		.addWithName("volume", "vol")
		.add("price"));
model.setFromClause(FromClause.create(FilterStream.create("OrderEvent)));

A second statement deletes from the named window: 

on NewOrderEvent as myNewOrders
delete from OrdersNamedWindow as myNamedWindow
where myNamedWindow.symbol = myNewOrders.symbol

The object model is built by: 

EPStatementObjectModel model = new EPStatementObjectModel();
model.setOnExpr(OnClause.createOnDelete("OrdersNamedWindow", "myNamedWindow"));
model.setFromClause(FromClause.create(FilterStream.create("NewOrderEvent", "myNewOrders")));
model.setWhereClause(Expressions.eqProperty("myNamedWindow.symbol", "myNewOrders.symbol"));

A third statement selects from the named window using the non-continuous on-demand selection via on-select: 

on QueryEvent(volume>0) as query
select count(*) from OrdersNamedWindow as win
where win.symbol = query.symbol

The on-select statement is built from scratch via the object model as follows: 

EPStatementObjectModel model = new EPStatementObjectModel();
model.setOnExpr(OnClause.createOnSelect("OrdersNamedWindow", "win"));
model.setWhereClause(Expressions.eqProperty("win.symbol", "query.symbol"));
model.setFromClause(FromClause.create(FilterStream.create("QueryEvent", "query", 
  Expressions.gt("volume", 0))));
model.setSelectClause(SelectClause.create().add(Expressions.countStar()));

15.8. Substitution Parameters

Substitution parameters have the following syntax: 

? [:[name] [:type]]

The name is optional. The absence of a name means the substitution parameter is only addressable by index.

The type is optional. The absence of the type means the type of the substitution parameter is java.lang.Object. Use cast or provide a type name when your expression requires a strongly-typed value.

Here are a few examples of valid substitution parameters:

Table 15.2. Valid Substitution Parameters

ValueDescription
?
Unnamed and typed Object.
?::int
Unnamed and typed int.
?:param:string
Named and typed string.

All substitution parameters must either be unnamed or named. It is not possible to mix the two styles.

If not assigning a name to substitution parameters, the compiler assigns the first substitution parameter an index of 1 and subsequent parameters increment the index by one.

If assigning a name to each substitution parameter, the name can include slash (/) characters and can occur multiple times.

Substitution parameters can be inserted into any EPL construct that takes an expression. They are therefore valid in any clauses such as the select-clause, from-clause filters, where-clause, group-by-clause, having-clause or order-by-clause, including data window parameters and pattern observers and guards, for example. Substitution parameters cannot be used where a numeric constant is required rather than an expression and in SQL statements.

You may use square brackets ([]) to denote array-types and [primitive] for array of primitive. For example int[primitive] for array of int-primitive and int[] for array of Integer.

All substitution parameters must be replaced by actual values at time of deployment.

15.9. OSGi, Class Loader, Class-For-Name

The configuration object (Configuration), in respect to classes, holds the fully-qualified class name and does not generally hold Class references. This is by design since the configuration object can be populated from XML.

The compiler may need to look up a class by name and may need to obtain a class loader. Your application has full control over class-for-name and classloader use. OSGi environments can provide a specific class-for-name and class loader. Please refer to Section 17.7, “Passing Services or Transient Objects”.

15.10. Authoring Tools

Enterprise Edition includes authoring tools for statements and modules by providing form-based dialogs, templates, an expression builder, simulation tool and other tools. Enterprise Edition also supports hot deployment and packaging options for EPL and related code.

Statements can be organized into modules as described above. Any text editor can edit statements and module text. A text editor or IDE that highlights SQL syntax or keywords works.

For authoring configuration files please consult the XSD schema files as provided with the distribution.

For information on authoring event classes or event definitions in general please see Chapter 3, Event Representations or Section 5.15, “Declaring an Event Type: Create Schema”.

15.11. Testing Tools

We recommend testing modules using a test framework such as JUnit or TestNG. Please consult the regression test suite for extensive examples, which can be downloaded from the distribution site.

Esper's API provides test framework classes to simplify automated testing of statements. Please see Section 16.18, “Test and Assertion Support” for more information.

We recommend performing latency and throughput tests early in the development lifecycle. Please consider the performance tips in Chapter 23, Performance for optimal performance.

Consider runtime and statement metrics reporting for identifying slow-performing statements, for example. See Section 16.12, “Runtime and Statement Metrics Reporting”.

15.12. Debugging

Enterprise Edition includes a debugger for module execution.

One important tool for debugging without Enterprise Edition is the parameterized @Audit annotation. This annotation allows to output, on statement-level, detailed information about many aspects of statement processing.

Another tool for logging runtime-level detail is Section 17.6.2.1, “Execution Path Debug Logging”.

Please see Section 17.9, “Logging Configuration” for information on configuring logging in general.

Use the @Audit annotation to have the runtime output detailed information about statement processing. The runtime reports, at INFO level, the information under log name com.espertech.esper.audit. You may define an output format for audit information via configuration.

You may provide a comma-separated list of category names to @Audit to output information related to specific categories only. The table below lists all available categories. If no parameter is provided, the runtime outputs information for all categories. Category names are not case-sensitive.

For the next statement the runtime produces detailed processing information (all categories) for the statement: 

@Name('All Order Events') @Audit select * from OrderEvent

For the next statement the runtime provides information about new events and also about event property values (2 categories are listed): 

@Name('All Order Events') @Audit('stream,property') select price from OrderEvent

Here is a more complete example that uses the API to create the schema, create above statement and send an event: 

try {
  String module =
    "@public @buseventtype create schema OrderEvent(price double);\n" +
    "@name('All-Order-Events') @Audit('stream,property') select price from OrderEvent;\n";
  EPCompiled compiled = EPCompilerProvider.getCompiler().compile(module, null);

  EPRuntime runtime = EPRuntimeProvider.getDefaultRuntime();
  EPDeployment deployment = runtime.getDeploymentService().deploy(compiled);
  deployment.getStatements()[0].addListener(new SupportUpdateListener());
  runtime.getEventService().sendEventMap(Collections.singletonMap("price", 100d), "OrderEvent");
} catch (Throwable t) {
  log.error(t.getMessage(), t);
}

The output is similar to the following: 

INFO  [audit] Statement All-Order-Events stream OrderEvent inserted {price=100.0}
INFO  [audit] Statement All-Order-Events property price value 100.0

Table 15.3. @Audit Categories

CategoryDescription
ContextPartitionEach context partition allocation and de-allocation (only for statements that declare a context).
Dataflow-SourceEach data flow source operator providing an event.
Dataflow-OpEach data flow operator processing an event.
Dataflow-TransitionEach data flow instance state transition.
ExprdefEach expression declaration name and return value.
ExpressionEach top-level expression and its return value.
Expression-nestedEach expression including child or nested expressions and their return value.
InsertEach event inserted via insert-into.
PatternEach pattern sub-expression and its change in truth-value.
Pattern-instancesEach pattern sub-expression and its count of active instances.
PropertyEach property name and the event's property value.
ScheduleEach schedule modification and trigger received by a statement.
StreamEach new event received by a statement.
ViewEach data window name and its insert and remove stream.

Note that the runtime only evaluates select-clause expressions if either a listener or subscriber is attached to the statement or if used with insert-into.

15.13. Ordering Multiple Modules

Since modules may have inter-dependencies as discussed under the uses declaration, there is a ModuleOrderUtil class that provides the getModuleOrder method to order a collection of modules before deployment.

Assuming your application reads multiple modules into a mymodules module list, this code snippet orders the modules for deployment and validates dependency declarations for each module: 

List<Module> mymodules =  ... read modules...;  
ModuleOrder order = ModuleOrderUtil.getModuleOrder(mymodules, new ModuleOrderOptions());

15.14. Logging

You can log generated classes at INFO log level by setting the configuration flag for code logging as described in Section 17.5.3.1, “Byte Code Generation Logging”.

15.15. Debugging Generated Code

The information herein is for developers and is specific to the Janino compiler at the version provided with the distribution.

Set the system property org.codehaus.janino.source_debugging.enable to true to have Janino compile code with debug symbols.

Set the system property org.codehaus.janino.source_debugging.dir to a file system directory to have Janino generate classes into a given directory.

The IDE can debug into generated classes and show the source code provided that the IDE can access the source code. For example: 

-Dorg.codehaus.janino.source_debugging.dir=/path/to/directory
-Dorg.codehaus.janino.source_debugging.enable=true

To include additional EPL-related comments in the generated code you can change the configuration as outlined in Section 17.5.1, “Compiler Settings Related to Byte Code Generation”.

15.16. Compiler Version and Runtime Version

The version format is major.minor.patch-level.

When deploying a compiled module to a runtime, or when executing a compiled fire-and-forget query, the runtime compares the compiler version that produced the compiled module or compiled query with the runtime version. If the major or minor version does not match, the runtime indicates a version mismatch by throwing an exception.

For example, an application may compile an EPL module using the version 8.0.0 compiler, i.e. the compiler major version is eight and the compiler minor version is zero and the compiler patch level is zero. Assume the application attempts to deploy the compiled module to a runtime of version 8.1.0, i.e. the runtime major version is eight and the runtime minor version is one and the runtime patch level is zero. The runtime throws an EPDeployDeploymentVersionException exception to indicate that the minor version mismatches.

15.17. Generated Code Optimizations

The compiler generates code that avoids down-casts and branching. It also removes many virtual calls as it transforms expression trees into byte code.

For aggregations the compiler produces a custom aggregation row class that has fields which represent the aggregation state. Therefore each aggregation row does not need additional objects to represent aggregations such as averages or sums and instead the aggregations are fields of the same class, reducing the number objects that the runtime manages per group-by key.