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Ask the right questions to secure the right EPL (Event Processing Language) talent among an increasingly shrinking pool of talent.
EPL (Event Processing Language) is a high-level programming language specifically designed for complex event processing (CEP). Developed by EsperTech, it allows users to process and analyze multiple streams of data in real-time. EPL's syntax is similar to SQL, making it easily accessible for developers familiar with database querying. Its primary use lies in scenarios where vast amounts of streaming data need to be processed quickly and efficiently, such as financial services or IoT applications. The language has been open-source since its inception, promoting widespread adoption across various industries.
The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.
The 'group by' clause in EPL is used to group events by one or more properties. It is often used with aggregation functions to perform calculations on each group of events.
The 'insert into' statement in EPL is used to insert events into a named window or stream.
'Window' is used to hold the last N events for a period of time, while 'retain-union' is used to hold all events from both named windows until they are explicitly deleted.
In EPL, an event is defined as an occurrence of a specific action or a change in state. It can be represented as a data object with a set of properties.
The basic components of an EPL statement are: Event Stream, Filter, Window, Output, and Pattern.
Meeting deadlines is crucial in a developer role. The candidate should provide examples of when they successfully met a deadline.
The ability to learn new technologies quickly is important in a rapidly changing field like software development. The candidate should provide examples of when they had to learn a new technology quickly.
Experience with real-time event processing is important for an EPL developer. The candidate should be able to discuss their experience in this area.
Teamwork is often necessary in a developer role. The candidate should show that they can communicate effectively and collaborate with others.
Problem-solving skills are important for a developer position. The candidate should be able to describe how they would approach and solve a complex problem.
A strong understanding of EPL is crucial for the role. The candidate should be able to explain the language's syntax, semantics, and use cases.
The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.
The 'merge' statement in EPL is used to update, insert, or delete events in a named window or stream based on a condition.
'Every' is used to match every occurrence of an event, while 'every-distinct' is used to match every distinct occurrence of an event based on one or more properties.
The 'having' clause in EPL is used to filter the results of a 'group by' clause based on a condition. It is similar to the 'where' clause, but operates on the results of aggregations.
Complex event processing in EPL can be handled using patterns and subqueries to detect complex sequences of events and perform calculations on them.
The different types of windows in EPL are: Sliding Window, Tumbling Window, and Batch Window. They are used to hold events for a period of time or until a certain condition is met.
A skilled EPL engineer should exhibit proficiency in complex event processing, strong coding abilities especially in Java or C#, and a deep understanding of database systems. Red flags include lack of practical experience, poor problem-solving skills, and difficulty explaining complex processes clearly.
select * from StockTickselect avg(price) from StockTick.win:time(30 sec)select * from pattern [every a=StockTick -> b=StockTick(a.symbol = b.symbol and a.price < b.price)]select * from StockTick#unique(symbol) retain-unionselect a.symbol, a.price, b.price from pattern [every a=StockTick -> b=StockTick(a.symbol = b.symbol)]select * from StockTick#time(10 min) where price > (select avg(price) from StockTick#time(30 min))The final few interview questions for a EPL (Event Processing Language) candidate should typically focus on a combination of technical skills, personal goals, growth potential, team dynamics, and company culture.
Performance of EPL queries can be optimized by using indexed windows for faster access to events, using subqueries and joins efficiently, and minimizing the use of 'every' in patterns.
'First' is used to select the first event in a window or stream, while 'last' is used to select the last event. They can be used with a number to select the Nth first or last event.
The 'context' statement in EPL is used to define a context under which certain EPL statements should be executed. It allows for more granular control over event processing.
Time-based events in EPL can be handled using time windows, timers, and temporal patterns to process events based on their timestamps.
The different types of joins in EPL are: Inner Join, Outer Join, and Full Join. They are used to combine events from two or more streams based on a condition.
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