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Developing an Application

 

 

OutSystems

Caching

You can improve the performance of your app by enabling the caching of some elements. The cache improves the performance by temporarily storing already retrieved or calculated data in fast memory and making that data available for an efficient loading in future requests.

Caching is RAM-based and is available in every front-end server. Whenever memory space is required, the elements are removed from the cache using the least recently used algorithm.

There is a specific cache for each tenant in the multitenant apps, which only stores data related to it. You can invalidate the cache in the multitenant environments by using System Actions EspaceInvalidateCache and TenantInvalidateCache.

These are the elements that support caching:

  • The lists returned by Aggregate and SQL.
  • Output parameters of custom Server Actions.
  • Web Blocks and elements they contain (Traditional Web Apps only).

Some elements don't support caching. These are:

  • Screens, as the feature currently does not support this element.
  • Web Blocks with Submit or Ajax Submit.

Notes about SOAP

We recommend that you encapsulate SOAP Web Service into a Server Action. Then, activate caching for that Server Action.

There are two SOAP Web Service implementations, with different support for caching:

  • Legacy SOAP Web Service implementation, which you can recognize by "(Deprecated)" in the name. This implementation does support caching. However, if you have to use this legacy feature and cache the output, we still recommend encapsulating it in a cached Server Action.
  • New Soap Web Service. This implementation does not support caching, and you should encapsulate it in a cached Server Action if you want to use caching.

Activating the caching feature

To start caching the content of an element, set the Cache in Minutes property to a value greater than zero.

Cache settings showing Cache in minutes property

The caching mechanism

This is how the cache works:

  • On the first use, the element is evaluated and the resulting content is stored in the cache.
  • On the following uses, the stored content is returned by the server while skipping the evaluation.

Any cached element is evaluated again, and the resulting content is updated in the cache when:

  • The elapsed time since the element content was last cached exceeds the element's Cache in Minutes value.
  • The element has input parameters and there's no cached content for their new values.
  • The cache is invalidated (for example: after republishing, deployment, server restart, explicit calls to invalidate the cache).

Additionally:

  • Web Blocks of the Traditional Apps cache the content of all elements they contain. However, if the content of any of these elements changes, the cache won't be automatically updated. The cache is refreshed only when the whole Web Block is evaluated again.
  • The cached elements cannot have input parameters of the following types: Record, List, and Binary Data.

Cache in producer and consumer modules

The cache also depends on whether the producer module is referenced as a strong or a weak dependency.

When the modules have a strong dependency, the Action logic is executed in the context of each consumer module handling the request. The cached value exists in each of the producers and cannot be reused between them.

If you want a single cached value instance in memory and serve all requests with it, expose the Action through a weak dependency. This way, the request executing and caching the Action exists only in the producer module, and all its consumers see the same value.

Examples

You can consider caching the contents of:

  • Elements with an execution time that negatively impacts the end-user experience
  • Elements that overload the system resources (database, CPU, memory...)
  • Elements that fetch data from databases or external systems
  • Elements for which the returned results rarely change or change in a controlled way for the same input parameters

Here are some examples of these situations:

  • A Web Block with a list of categories that are stored in the database.
  • A method of a consumed SOAP Web Service that fetches job opportunities from an external system.
  • A method consumed from a SOAP Web Service that returns the list of employees.
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