The runtime takes on these functions:

Your application obtains a runtime from EPRuntimeProvider. You may pass an arbitrary string-type runtime URI that uniquely identifies the runtime instance.

A runtime is an instance of EPRuntime. Use the runtime as follows:

A compiled module contains zero, one or multiple statements. You can attach callbacks (listeners, subscribers) to statements to receive results (aka push, observer pattern). You can iterate statement current results (aka. poll).

Each statement is uniquely identified in the runtime by the combination of deployment id and statement name. The compiler or runtime always assign a statement name if none was provided.

The EPStatement instance represents the statement. Your application receives statements when deploying a module by calling getStatements on EPDeployment.

Your application may also look up a statement by it's deployment id and statement name using the getStatement method on EPDeploymentService.

select count(*) from OrderEvent

public void update(EPStatement statement, long currentCount) {...}

select orderId, price, count(*) from OrderEvent

public class MySubscriber {
  ...
  public void update(String orderId, double price, long count) {...}
  ...
}

select *, count(*) from OrderEvent

public void update(OrderEvent orderEvent, long count) {...}

select *, count(*) from OrderEvent order, OrderHistory hist

public void update(OrderEvent orderEvent, OrderHistory orderHistory, long count) {...}

select hist.*, order from OrderEvent order, OrderHistory hist

public void update(OrderHistory orderHistory, OrderEvent orderEvent) {...}

public void update(Map row) {...}

public void update(Object[] row) {...}

select orderId, count(*) from OrderEvent#time(20 sec) group by orderId

public void update(String, long count) {...}
public void updateRStream(String orderId, long count) {...}

// Called by the runtime before delivering events to update methods
public void updateStart(int insertStreamLength, int removeStreamLength)

// To deliver insert stream events
public void update(String orderId, long count) {...}

// To deliver remove stream events
public void updateRStream(String orderId, long count) {...}

// Called by the runtime after delivering events
public void updateEnd() {...}

select * from OrderEvent#time(30 sec)

public void update(OrderEvent[] insertStream, OrderEvent[] removeStream) {...}

select null from OrderEvent(price > 100)

public void update() {...}

UpdateListener myListener = new MyUpdateListener();
countStmt.addListener(myListener);

EPStatement statement = epAdmin.createEPL("select avg(price) as avgPrice from MyTick");
// .. send events into the runtime
// then use the pull API...
SafeIterator<EventBean> safeIter = statement.safeIterator();
try {
  for (;safeIter.hasNext();) {
     // .. process event ..
     EventBean event = safeIter.next();
     System.out.println("avg:" + event.get("avgPrice");
  }
}
finally {
  safeIter.close();	// Note: safe iterators must be closed
}

double averagePrice = (Double) eplStatement.iterator().next().get("average");

select symbol, avg(price) as avgprice, count(*) as mycount 
from StockTickEvent 
group by symbol

eventBean.get("symbol")

eventBean.get("avgprice")

eventBean.get("mycount")

String symbol = (String) newEvents[0].get("symbol");
Double price= (Double) newEvents[0].get("avgprice");
Long count= (Long) newEvents[0].get("mycount");

select * from StockTickEvent where price > 100

eventBean.get("symbol")

eventBean.get("price")

StockTickEvent tick = (StockTickEvent) newEvents[0].getUnderlying();

// Look for a pattern where BEvent follows AEvent
select * from pattern [a=AEvent -> b=BEvent]

// Example listener code
public class MyUpdateListener implements UpdateListener {
  public void update(EventBean[] newData, EventBean[] oldData, EPStatement statement, EPRuntime runtime) {
    System.out.println("a event=" + newData[0].get("a"));
    System.out.println("b event=" + newData[0].get("b"));
  }
}

select * from pattern[every a=A -> (timer:interval(60 sec) and not B(id=a.id))]

EventBean a = (EventBean) newEvents[0].getFragment("a");
// ... or using a nested property expression to get a value out of A event...
double value = (Double) newEvent[0].get("a.value");

select * from pattern [a=A until b=B]

EventBean[] a = (EventBean[]) newEvents[0].getFragment("a");
// ... or using a nested property expression to get a value out of A event...
double value = (Double) newEvent[0].get("a[0].value");

String exampleEPL = "@Tag(name='direct-output', value='sink 1') select * from RootEvent";
Configuration configuration = new Configuration();
configuration.getCommon().addEventType("RootEvent", Collections.emptyMap()); // add an event type without properties
CompilerArguments compilerArguments = new CompilerArguments(configuration);
EPCompiled compiled = EPCompilerProvider.getCompiler().compile(stmt, compilerArguments);

EPDeployment deployment = runtime.getDeploymentService().deploy(compiled);
EPStatement stmt = deployment.getStatements()[0];
for (Annotation annotation : stmt.getAnnotations()) {
  if (annotation instanceof Tag) {
    Tag tag = (Tag) annotation;
    System.out.println("Tag name " + tag.name() + " value " + tag.value());
  }
}

This section focuses on processing events. For more information on controlling time using the event service please skip forward to Section 16.9, “Controlling Time-Keeping”.

Your application invokes any of the sendEventType methods listed below and must provide an event type name along with the actual event object:

sendEventBean(Object event, String eventTypeName)

sendEventMap(Map<String, Object> event, String eventTypeName)

sendEventObjectArray(Object[] event, String eventTypeName);

sendEventXMLDOM(Node node, String eventTypeName);

void sendEventJson(String json, String jsonEventTypeName);

void sendEventAvro(Object avroGenericDataDotRecord, String avroEventTypeName);

The Chapter 3, Event Representations section explains the types of event representations.

The below sample code assumes that the event type name MarketDataBean refers to a class event representation that matches the class MarketDataBean:

EPRuntime runtime = EPRuntimeProvider.getDefaultRuntime();
EPEventService eventService = runtime.getEventService();

// Send an example event containing stock market data
eventService.sendEventBean(new MarketDataBean("IBM", 75.0), "MarketDataBean");

EventSender sender = runtime.getEVentService().getEventSender("MyEvent");
sender.sendEvent(myEvent);

select * from MyEvent(quantity > 5)

Esper provides the facility to explicitly index named windows and tables to speed up fire-and-forget queries and statements. Please consult Section 6.9, “Explicitly Indexing Named Windows and Tables” for more information.

When named windows and tables are used with contexts and context partitions, the APIs to identify, filter and select context partitions for fire-and-forget queries can be found in Section 16.16, “Context Partition Selection”.

There are three ways to run fire-and-forget queries:

If your application must execute the same fire-and-forget query multiple times with different parameters use prepareQueryWithParameters.

If your application must execute the same fire-and-forget query multiple times without parameters use either prepareQuery or prepareQueryWithParameters and specify no substitution parameters.

By using any of the prepare... methods the runtime can load the byte code for the query once and reuse the byte code and thereby speed up repeated execution.

The following limitations apply:

String query = "select * from MyNamedWindow";
CompilerArguments compilerArguments = new CompilerArguments();
compilerArguments.getPath().add(runtime.getRuntimePath());
EPCompiled compiled = EPCompilerProvider.getCompiler().compileQuery(query, compilerArguments);

EPFireAndForgetQueryResult result = runtime.getFireAndForgetService().executeQuery(compiled);
for (EventBean row : result.getArray()) {
  System.out.println("name=" + row.get("name"));
}

String query = "select * from MyNamedWindow where orderId = '123'";
CompilerArguments compilerArguments = new CompilerArguments();
compilerArguments.getPath().add(runtime.getRuntimePath());
EPCompiled compiled = EPCompilerProvider.getCompiler().compileQuery(query, compilerArguments);
						
EPFireAndForgetPreparedQuery prepared = runtime.getFireAndForgetService().prepareQuery(compiled);
EPFireAndForgetQueryResult result = prepared.execute();

// ...later on execute once more ...
prepared.execute();	// execute a second time

String query = "select * from MyNamedWindow where orderId = ?::string";
CompilerArguments compilerArguments = new CompilerArguments();
compilerArguments.getPath().add(runtime.getRuntimePath());
EPCompiled compiled = EPCompilerProvider.getCompiler().compileQuery(query, compilerArguments);

EPFireAndForgetPreparedQueryParameterized prepared = runtime.getFireAndForgetService().prepareQueryWithParameters(query);

// Set the required parameter values before each execution
prepared.setObject(1, "123");
EPFireAndForgetQueryResult result = runtime.getFireAndForgetService().executeQuery(prepared);

// ...execute a second time with new parameter values...
prepared.setObject(1, "456");
result = runtime.getFireAndForgetService().executeQuery(prepared);

String query = "select * from MyNamedWindow where orderId in (?::string[]) and price > ?::double";
CompilerArguments compilerArguments = new CompilerArguments();
compilerArguments.getPath().add(runtime.getRuntimePath());
EPCompiled compiled = EPCompilerProvider.getCompiler().compileQuery(query, compilerArguments);

EPFireAndForgetPreparedQueryParameterized prepared = runtime.getFireAndForgetService().prepareQueryWithParameters(compiled);
prepared.setObject(1, new String[] {"123", "456"});
prepared.setObject(2, 1000.0);

For NEsper .NET also see Section J.16, “.NET API - Runtime Threading and Concurrency”.

The runtime is designed from the ground up to operate as a component to multi-threaded, highly-concurrent applications that require efficient use of Java VM resources. In addition, multi-threaded execution requires guarantees in predictability of results and deterministic processing. This section discusses these concerns in detail.

In Esper, a runtime instance is a unit of separation. Applications can obtain and discard (initialize) one or more runtime instances within the same Java VM and can provide the same or different configurations to each instance. A runtime instance shares resources between statements by means of named windows, tables and variables.

Applications can use Esper APIs to concurrently, by multiple threads of execution, perform such functions as deploying modules, or sending events into the runtime for processing. Applications can use application-managed threads or thread pools or any set of same or different threads of execution with any of the public runtime APIs. There are no restrictions towards threading other than those noted in specific sections of this document.

The runtime does not prescribe a specific threading model. Applications using Esper retain full control over threading, allowing a runtime to be easily embedded and used as a component or library in your favorite Java container or process.

In the default configuration it is up to the application code to use multiple threads for processing events by the runtime, if so desired. All event processing takes places within your application thread call stack. The exception is timer-based processing if your runtime relies on the internal timer (default). If your application relies on external timer events instead of the internal timer then there need not be any runtime-managed internal threads.

The fact that event processing can take place within your application thread's call stack makes developing applications with the Esper runtime easier: Any common Java integrated development environment (IDE) can host a compiler and runtime instance. This allows developers to easily set up test cases, debug through listener code and inspect input or output events, or trace their call stack.

In the default configuration, each runtime maintains a single timer thread (internal timer) providing for time or schedule-based processing within the runtime. The default resolution at which the internal timer operates is 100 milliseconds. The internal timer thread can be disabled and applications can instead advance time to perform timer or scheduled processing at the resolution required by an application.

A runtime performs minimal locking to enable high levels of concurrency. A runtime locks on the combination of query and context partition to protect context partition resources. For example, two statements with three partitions each have a total of six locks. For stateless EPL select-statements the runtime does not use a context-partition lock and operates lock-free for the context partition. For stateful statements, the maximum (theoretical) degree of parallelism is 2^31-1 (2,147,483,647) parallel threads working to process a single statement under a hash segmented context.

For named windows and tables, on-select, on-merge, on-update and on-delete all execute under the same lock as the partition of the named window or table. Any insert into produces a new event for the work queue and does not lock the target of the insert-into.

You may turn off context partition locking runtime-wide (also read the caution notice) as described in Section 17.6.10.3, “Disable Locking”. You may disable context partition locking for a given statement by providing the @NoLock annotation as part of your EPL. Note, Esper provides the @NoLock annotation for the purpose of identifying locking overhead, or when your application is single-threaded, or when using an external mechanism for concurrency control or for example with virtual data windows or plug-in data windows to allow customizing concurrency for a given statement or named window. Using this annotation may have unpredictable results unless your application is taking concurrency under consideration.

For a runtime to produce predictable results from the viewpoint of listeners to statements, a runtime by default ensures that it dispatches statement result events to listeners in the order in which a statement produced result events. Applications that require the highest possible concurrency and do not require predictable order of delivery of events to listeners, this feature can be turned off via configuration, see Section 17.6.1.1, “Preserving the Order of Events Delivered to Listeners”. For example, assume thread T1 processes an event applied to statement S producing output event O1. Assume thread T2 processes another event applied to statement S and produces output event O2. The runtime employs a configurable latch system to ensure that listeners to statement S receive and may complete processing of O1 before receiving O2. When using outbound threading (advanced threading options) or changing the configuration this guarantee is weakened or removed.

In multithreaded environments, when one or more statements make result events available via the insert into clause to further statements, the runtime preserves the order of events inserted into the generated insert-into stream, allowing statements that consume other statement's events to behave deterministic. This feature can also be turned off via configuration, see Section 17.6.1.2, “Preserving the Order of Events for Insert-Into Streams”. For example, assume thread T1 processes an event applied to statement S and thread T2 processes another event applied to statement S. Assume statement S inserts into stream ST. T1 produces an output event O1 for processing by consumers of ST1 and T2 produces an output event O2 for processing by consumers of ST. The runtime employs a configurable latch system such that O1 is processed before O2 by consumers of ST. When using route execution threading (advanced threading options) or changing the configuration this guarantee is weakened or removed.

We generally recommended that listener implementations block minimally or do not block at all. By implementing listener code as non-blocking code execution threads can often achieve higher levels of concurrency.

We recommended that, when using a single listener or subscriber instance to receive output from multiple statements, that the listener or subscriber code is multithread-safe. If your application has shared state between listener or subscriber instances then such shared state should be thread-safe.

EPRuntimeSPI spi = (EPRuntimeSPI) runtime;
int queueSize = spi.getThreadingService().getInboundQueue().size();
ThreadPoolExecutor threadpool = spi.getThreadingService().getInboundThreadPool();

You may register one or more exception handlers for the runtime to invoke in the case it encounters an exception processing a continuously-executing statement. By default and without exception handlers the runtime cancels execution of the current statement that encountered the exception, logs the exception and continues to the next statement, if any. The configuration is described in Section 17.6.11, “Runtime Settings Related to Exception Handling”.

If your application registers exception handlers as part of runtime configuration, the runtime invokes the exception handlers in the order they are registered passing relevant exception information such as statement name, expression and the exception itself.

Exception handlers receive any statement unchecked exception such as internal exceptions or exceptions thrown by plug-in aggregation functions or plug-in data windows. The runtime does not provide to exception handlers any exceptions thrown by static method invocations for function calls, method invocations in joins, methods on variables and event classes and listeners or subscriber exceptions.

An exception handler can itself throw a runtime exception to cancel execution of the current event against any further statements.

For fire-and-forget queries the API indicates any exception directly back to the caller without the exception handlers being invoked, as exception handlers apply to statements only. The same applies to any API calls other than sendEvent and the EventSender methods.

As the configuration section describes, your application registers one or more classes that implement the ExceptionHandlerFactory interface in the runtime configuration. Upon runtime initialization the runtime obtains a factory instance from the class name that then provides the exception handler instance. The exception handler class must implement the ExceptionHandler interface.

You may register one or more condition handlers for the runtime to invoke in the case it encounters certain conditions, as outlined below, when executing a statement. By default and without condition handlers the runtime logs the condition at informational level and continues processing. The configuration is described in Section 17.6.12, “Runtime Settings Related to Condition Handling”.

If your application registers condition handlers as part of runtime configuration, the runtime invokes the condition handlers in the order they are registered passing relevant condition information such as statement name, expression and the condition information itself.

Currently the only conditions indicated by this facility are raised by the pattern followed-by operator, see Section 7.5.8.1, “Limiting Sub-Expression Count” and see Section 7.5.8.2, “Limiting Runtime-Wide Sub-Expression Count”.

A condition handler may not itself throw a runtime exception or return any value.

As the configuration section describes, your application registers one or more classes that implement the ConditionHandlerFactory interface in the runtime configuration. Upon runtime initialization the runtime obtains a factory instance from the class name that then provides the condition handler instance. The condition handler class must implement the ConditionHandler interface.

The runtime can report key processing metrics through the JMX platform mbean server by setting a single configuration flag described in Section 17.6.7, “Runtime Settings Related to JMX Metrics”. For additional detailed reporting and metrics events, please read on.

Metrics reporting is a feature that allows an application to receive ongoing reports about key runtime-level and statement-level metrics. Examples are the number of incoming events, the CPU time and wall time taken by statement executions or the number of output events per statement.

Metrics reporting is, by default, disabled. To enable reporting, please follow the steps as outlined in Section 17.6.8, “Runtime Settings Related to Metrics Reporting”. Metrics reporting must be enabled at runtime initialization time. Reporting intervals can be controlled at runtime via the EPMetricsService interface available from the runtime API.

Your application can receive metrics at configurable intervals via statement. A metric datapoint is simply a well-defined event. The events are RuntimeMetric and StatementMetric and the Java class representing the events can be found in the client API in package com.espertech.esper.common.client.metric.

Since metric events are processed by the runtime the same as application events, your EPL may use any construct on such events. For example, your application may select, filter, aggregate properties, sort or insert into a stream, named window or table all metric events the same as application events.

This example statement selects all runtime metric events:

select * from RuntimeMetric

The next statement selects all statement metric events:

select * from StatementMetric

Make sure to have metrics reporting enabled since only then do listeners or subscribers to a statement such as above receive metric events.

The runtime provides metric events after the configured interval of time has passed. By default, only started statements that have activity within an interval (in the form of event or timer processing) are reported upon.

The default configuration performs the publishing of metric events in an Esper daemon thread under the control of the runtime instance. Metrics reporting honors externally-supplied time, if using external timer events.

Via runtime configuration options provided by EPMetricsService, your application may enable and disable metrics reporting globally, provided that metrics reporting was enabled at initialization time. Your application may also enable and disable metrics reporting for individual statements by statement name.

Statement groups is a configuration feature that allows to assigning reporting intervals to statements. Statement groups are described further in the Section 17.6.8, “Runtime Settings Related to Metrics Reporting” section. Statement groups cannot be added or removed at runtime.

The following limitations apply:

Enterprise Edition has a library for measuring and reporting memory use for a runtime.

The runtime can report key processing metrics through the JMX platform mbean server by setting a single configuration flag described in Section 17.6.7, “Runtime Settings Related to JMX Metrics”.

Runtime and statement-level metrics reporting is described in Section 16.12, “Runtime and Statement Metrics Reporting”.

The easiest way to see thread contentions is by using VisualVM when Esper is under load and looking at the Threads tab. In the worst case you will see a lot of red color in VisualVM. The red line in VisualVM shows the threads that are either in a monitor region or waiting in an entry set for the monitor. The monitor is the mechanism that Java uses to support synchronization. When a statement is stateful the runtime manages the state using a monitor (lock) per context partition.

A JVM profiler can be handy to see how much CPU is spent in Esper by the sendEvent method.

The jconsole can provide information on the JVM heap. If memory gets tights the performance can drop significantly.

The EPRenderEventService interface offers methods to render events as XML or JSON. Obtain the service from a runtime by calling getRenderEventService on EPRuntime.

Your application may use the built-in XML and JSON formatters to render output events into a readable textual format, such as for integration or debugging purposes. This section introduces the utility classes in the client util package for rendering events to strings. Further API information can be found in the JavaDocs.

For repeated rendering of events of the same event type or subtypes, it is recommended to obtain a JSONEventRenderer or XMLEventRenderer instance and use the render method provided by the interface. This allows the renderer implementations to cache event type metadata for fast rendering.

This example shows how to obtain a renderer for repeated rendering of events of the same type, assuming that statement is an instance of EPStatement:

JSONEventRenderer jsonRenderer = runtime.getRenderEventService().getJSONRenderer(statement.getEventType());

Assuming that event is an instance of EventBean, this code snippet renders an event into the JSON format:

String jsonEventText = jsonRenderer.render("MyEvent", event);

The XML renderer works the same:

XMLEventRenderer xmlRenderer = runtime.getRenderEventService().getXMLRenderer(statement.getEventType());

...and...

String xmlEventText = xmlRenderer.render("MyEvent", event);

If the event type is not known in advance or if your application does not want to obtain a renderer instance per event type for fast rendering, your application can use one of the following methods to render an event to a XML or JSON textual format:

String json = runtime.getRenderEventService().renderJSON(event);
String xml = runtime.getRenderEventService().renderXML(event);

Use the JSONRenderingOptions or XMLRenderingOptions classes to control how events are rendered. To render specific event properties using a custom event property renderer, specify an EventPropertyRenderer as part of the options that renders event property values to strings. Please see the JavaDoc documentation for more information.

This chapter discusses how to select context partitions. Contexts are discussed in Chapter 4, Context and Context Partitions and the reasons for context partition selection are introduced in Section 4.9, “Operations on Specific Context Partitions”.

The section is only relevant when you declare a context. It applies to all different types of hash, partitioned, category, overlapping or other temporal contexts. The section uses a category context for the purpose of illustration. The API discussed herein is general and handles all different types of contexts including nested contexts.

Consider a category context that separates bank transactions into small, medium and large:

// declare category context
create context TxnCategoryContext 
  group by amount < 100 as small, 
  group by amount between 100 and 1000 as medium, 
  group by amount > 1000 as large from BankTxn

// retain 1 minute of events of each category separately
context TxnCategoryContext select * from BankTxn#time(1 minute)

In order for your application to iterate one or more specific categories it is necessary to identify which category, i.e. which context partition, to iterate. Similarly for fire-and-forget queries, to execute fire-and-forget queries against one or more specific categories, it is necessary to identify which context partition to execute the fire-and-forget query against.

Your application may iterate one or more specific context partitions using either the iterate or safeIterate method of EPStatement by providing an implementation of the ContextPartitionSelector interface.

For example, assume your application must obtain all bank transactions for small amounts. It may use the API to identify the category and iterate the associated context partition:

ContextPartitionSelectorCategory categorySmall = new ContextPartitionSelectorCategory() {
    public Set<String> getLabels() {
      return Collections.singleton("small");
    }
  };
Iterator<EventBean> it = stmt.iterator(categorySmall);

Your application may execute fire-and-forget queries against one or more specific context partitions by using the executeQuery method on EPRuntime or the execute method on EPFireAndForgetPreparedQuery and by providing an implementation of ContextPartitionSelector.

Fire-and-forget queries execute against named windows and tables, therefore below statement creates a named window which the runtime manages separately for small, medium and large transactions according to the context declared earlier:

// Named window per category
context TxnCategoryContext create window BankTxnWindow#time(1 min) as BankTxn

The following code demonstrates how to fire a fire-and-forget query against the small and the medium category:

ContextPartitionSelectorCategory categorySmallMed = new ContextPartitionSelectorCategory() {
    public Set<String> getLabels() {
      return new HashSet<String>(Arrays.asList("small", "medium"));
    }
  };
runtime.getFireAndForgetService().executeQuery(
   "select count(*) from BankTxnWindow", 
   new ContextPartitionSelector[] {categorySmallMed});

The following limitations apply:

This chapter briefly discusses the API to manage context partitions. Contexts are discussed in Chapter 4, Context and Context Partitions.

The section is only relevant when you declare a context. It applies to all different types of hash, partitioned, category, overlapping or other temporal contexts.

The EPContextPartitionService interface offers methods to manage context partitions. Obtain the service from a runtime by calling getContextPartitionService on EPRuntime.

The context partition admin API allows an application to:

Please see the JavaDoc documentation for more information.

When deploying compiled modules the runtime may use a class loader to find resources. 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”.