Event Stream Processing

• Sliding windows: time, length, sorted, accumulating, time-ordering, externally-timed (value-based windowing)
• Tumbling windows: time, length and multi-policy
• Grouping, aggregation, sorting, filtering and merging of event streams
• Tailored SQL-like query language using insert into, select, from, where, group-by, having and order-by clauses
• Inner-joins and outer joins (left, right, full) of an unlimited number of streams or windows
• Subqueries including exists and in
• Output rate limiting and stabilizing, snapshot output
• Named windows allow sharing data windows between statements; Define multiple explicit entry and exit criteria for events

Event Pattern Matching

• Logical and temporal event correlation
• Crontab-like timer 'at' operator
• Lifecycle of pattern can be controlled by timer and via operators
• Pattern-matched events provided to listeners

Event Representations

• Supports event-type inheritance and polymorphism as provided by the Java language
• Events can be plain Java objects, XML (DOM and streaming through Apache Axiom) and java.util.Map including nested objects and hierarchical maps
• Event properties can be simple, indexed, mapped or nested - allows querying of deep Java object graphs and XML structures
• Dynamic properties allow dynamic typing of properties, supported by cast, instanceof and exists functions
• Applications can plug-in their own event representation and dynamic type resolution

Prepared statements and substitution parameters

• Precompile a statement with substitution parameters and efficiently start the parameterized statement multiple times

Statement Object Model

• A set of classes providing an object-oriented representation of a statement
• Full and complete specification of a statement via object model
• Round-trip from object model to statement text and back to object model
• Build, change or interrogate statements beyond the textual representation

Input Adapters

• CSV input adapter reads comma-separated value formats
  • simulate multiple event streams with timed, coordinated playback via timestamp column
  • load generator
  • preloading of reference data
• JMS input and output adapter based on Spring JMS templates

Other

• Executes a large number of simultaneous queries - Esper's query processor can run thousands of queries continuously and simultaneously on a single instance
• Relational database access via SQL-query joins with event streams
  • LRU (least-recently used) and expiry-time query result caches
  • Keyed cache entries for fast cache lookup
  • Engine indexes cached rows for fast filtering within a large number of SQL-query result rows
• Joins to method invocation results allows easy integration with distributed caches, web services and object-oriented databases
• Variables can occur in any expression and can dynamically control output rate
  • Guarantees of consistency and atomicity of variable updates
• Variant event streams allows treating disparate types of events as the same type, such as when the event type can only be known at runtime, when the event type is expected to vary, or when optional properties are desired.
• Support for update events that update, provide a new version or that revise an existing event held by an engine.
• Support for both the listener (push/subscription) API and the consumer (pull/receive) API for querying results
• Concurrency-safe iterator provides complete query capability for all statements
• Supports externally-provided time as well as Java system time, allowing applications full control over the concept of time within an engine
• Multithread-safe as of release 1.5
  • Multithreaded sends of events into an engine
  • Create, start and stop statements during operation without adversely impacting performance
  • Applications can retain full control over threading
  • Efficiently sharing resources between statements and low thread blocking
• Supports multiple independent Esper engines per JavaVM
• Pluggable architecture for event pattern and event stream analysis via user-defined functions, plug-in views, plug-in aggregation functions, plug-in pattern guards and plug-in pattern event observers, event instance methods
• Performance-minded design: query strategy analysis and index building; array-based collections; delta networks and many other techniques
  • Benchmark kit available for download; Performance testing results and tips see page in menu
• Unmatched event listener receives a callback if an event does not match any started statement

Excellent documentation

Many examples

• J2EE and non-J2EE, from many different domains
• Java Messaging Service (JMS) server shell demonstrates a multi-threaded JMS server with dynamic statement management using Java Management Extensions (JMX)

Supportive user and developer community

Performance tested