By Ricardo Ferreira on Jan 18, 2014
In the heart of OEP application development there is the understanding of the business events anatomy, the knowledge about its structure, frequency about when they happen, its relationship with other types of events and of course, its volume. Business events play a critical role in event-driven applications because they are the input for the problem that you are trying to solve. Without the business events, an event-driven application would be like a car engine without fuel.
When you are designing an EPN (Event Processing Network) of an OEP application, you are actually expressing the way about how the business events will be received, processed and perhaps transformed in some kind of output. Like any other technology, the behavior of this output depends heavily of which data you have used as input. For one specific volume, the EPN could work, for another volume, maybe not. For one specific ordering, the EPN could work, with another ordering, it could not. It will only work when the right set of events is being used.
Its very common the situation when you deploy the first version of your OEP application and after a while users start complaining about undesired results. This happens because no matter how many times you tested your application, you will never get close to the mass of events present in the customer environment. The ordering, volume, size, encoding and frequency of the events found in the customer environment is always different of that mass of events that you used during functional testing. If this situation happens to you, its time to think in a way to record those events and bring them back to the development environment to figure out what is wrong.
This article aims to explore the record and playback feature of Oracle Event Processing Platform. Through the examples shown here, you will be able to record and replay a mass of business events to simulate some behavior that maybe you have forgot to capture at your EPN. This feature is also pretty cool for prototyping scenarios. Instead of bringing with a you a simulator of events, you can just replay a recorded set of events and present your OEP application.
Configuring the OEP Default Provider
In order to the record and playback features work, OEP needs to relies in a repository in which events will be stored. To make the developer work easier, OEP brings out-of-the-box an default provider for this repository based on the Berkeley DB technology. Located inside of every OEP domain, there is an instance of Berkeley DB (aka "BDB") which can be adjusted through the configuration file of the domain. In most cases, you don't need to change anything before start using the record and playback features, but there is one catch that you should be aware of.
BDB stores each recorded event as an entry in this repository. Each entry has a default size of 1KB (1000 bytes) pre-defined in the moment that you create the domain. The information about the size of each entry is important in terms of performance and how BDB will growth its storage. So if you know the average size of your events, it is a good idea to inform the size of each entry in the domain configuration file. For instance, suppose that we are dealing with a mass of events with 32KB of average size for each event. You can adjust BDB editing the domain configuration file located in <DOMAIN_HOME>/<SERVER_NAME>/config/config.xml:
As you can see in the example above, you need to adjust the cache-size property of the bdb-config section. This property is measured in terms of bytes. The value of this property represents the amount of memory that BDB need to allocate for each entry.
Recording the Events
In order to record events, you need to access the OEP Visualizer Console of your domain. Log in onto the console and navigate to the EPN of the OEP application that you want to record events.
In the EPN of your OEP application, you can right-click any of the elements inside, no matter if it is an adapter, channel, processor or an cache. But make totally sense to record the events from the adapters perspective. They are the genesis of your EPN, and all the events that will flow through it will come from the adapters. Right-click the input adapter of your EPN and choose the "Record Event" option:
You will open the record tab of the adapter. In the bottom of the page, in a section named "Change Recording Schedule", you will find an button named "Add". Click on it.
Adding a new record configuration scheme enables the UI for full-filling some fields. Enter in the "DataSet Name" field the name of this recording session. This field will be used to construct the physical repository of BDB. You are also required to set the "Selected Event Type List" field. You need to describe in this field which incoming events you are expecting to record. After this you can click in the "Save" button.
We are all set to start recording. Double-check if there are events being sent to your OEP application and click in the "Start" button. Doing this will start a recording session and all events received by the adapter will be recorded. At any point of time, you can click in the "Stop" button to stop the recording session.
Playing Back the Events
To start the playback of any recorded session, you need to go back to the EPN screen and right-click the channel that will receive the events. This will bring you to the playback tab of the selected channel. Just like the recording session, you need to add one playback configuration scheme clicking in the "Add" button.
The group of fields to be full-filled is almost the same. Pay attemption that in the "DataSet Name" field you need to inform the exactly name that you informed in the recording session. Since you can have multiple recording sessions under different names, when you playback you need to tell OEP which session you would like to playback. As such, you need to inform which events you would like to playback, filling the "Selected Event Type List" field.
Optionally, you can set some additional parameters related to the behavior of the playback. In the "Change Playback Schedule Parameters" you can find fields to define which interval of time you want to playback. This is useful when you recorded hours/days of event streaming and you would like to reproduce just one piece of it. You can also define the speed in which events will be injected into the channel, useful to test how your EPN behave in a high speed velocity situation. Finally, you can set if the playback will be repeated forever. Since the recording session is finite, you can playback it as many times you want, or can just set the "Repeat" field as true to automatically restart from the beginning when the recorded streaming ends.
When you are done, save the playback configuration scheme and click in the "Start" button to start the playback session according your settings. An "Playing..." message will be flipping in the screen during the playback session. At any time, you can stop the playback clicking in the "Stop" button.
All the configuration you made so far is stored in the OEP domain along with your application so don't be shy to restart the OEP server and potentially lose your job: all the settings will remain there when the server come back to life. This statement is true as long you don't undeploy your application from the OEP domain. If you undeploy your application, all the settings will be lost. If you want make those settings permanent, you can set those into your application. Access this link to learn how to configure a component to record events, and this link to learn how to configure a component to playback events.